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SM2.2

Typical practice for seismic hazard assessment (SHA) in stable continental regions (SCRs) uses a global-analogues approach to amalgamate seismicity data from SCRs globally. This approach is premised on all SCR crust sharing the same seismogenic potential. Is this approach valid? How can we better define seismogenic analogues in low strain regions? Are earthquake recurrence and long-term slip rates meaningful concepts in these settings for the purpose of seismic hazard analysis?
This session seeks to integrate paleoseismic, geomorphic, geodetic, geophysical and seismological datasets to provide insight into the earthquake cycle in low-strain regions. It will draw upon recent advances in high-resolution topography, geochronology, satellite geodesy techniques, subsurface imaging techniques, longer seismological records, high-density geophysical networks and unprecedented computational power to explore the driving mechanisms for earthquakes in low-strain settings. A comparison of the range of seismic behavior as a function of the different geodynamic attributes of these settings (e.g., crustal age, structure, stress, geology, antecedent
tectonics (inheritance); evolving boundary conditions; Quaternary processes (glaciation), etc), may provide a means to better refine and constrain the types of features or active processes that warrant treatment as analogues for seismic hazard assessment. We welcome contributions that (1) present new observations that place constraints on earthquake occurrence in low-strain regions, (2) explore patterns of stable or temporally varying earthquake recurrence, and (3) provide insight into the mechanisms that control earthquakes in regions of slow deformation via observation and/or
modeling.

Public information:
The session will be hosted both on Zoom and on the EGU text-based chat.

Schedule :
- 10:45-11:15 : Zoom session (see link below) - Presentations only (no questions and answers, this will take place in the chat), presenters are invited to share their screen
- 11:15-12:30 : EGU chat session - questions and answers for all presenters

------------------------------------- Zoom session link ------------------------------------
Join from PC, Mac, Linux, iOS or Android: https://videoconf-colibri.zoom.us/j/98788480483
Or iPhone one-tap: 308810988,98788480483# or 211202618,98788480483#
Or Telephone:
Dial: +351 308 810 988 (Portugal Toll) or +351 211 202 618 (Portugal Toll)
Meeting ID: 987 8848 0483
International numbers available: https://videoconf-colibri.zoom.us/u/adNZCcmlD1
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The Zoom session will start with a 10 minute presentation by Eulalia Gracia for a solicited talk. It will be followed by 6 3-minute long presentations.
Then, we will switch to the text-based chat for questions and answers ; 5 minutes for each presentation. Each presentation will be introduced by the conveners.

The schedule is given below.

ZOOM (10:45-11:15) -
10:45-10:55 E. Gracia Earthquake crisis unveils the growth of an incipient continental fault system
10:55-10:58 J. Ritz The Mw4.9 Le Teil surface-rupturing earthquake in southern France: New insight on seismic hazard assessment in stable continental regions
10:58-11:01 A. Vallage Full characterization of the ML 5.4 2019/11/11 Le Teil earthquake in France based on a multi-technology approach
11:01-11:04 T. King The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake
11:04-11:07 C.-H. Tsai Palaeo-earthquake magnitudes on the Dzhungarian fault, N. Tien shan, and implications for the rupture processes of intraplate strike-slip faults
11:07-11:10 C. Daxer Quantitative paleoseismology in Carinthia, Eastern Alps: Calibrating the lacustrine sedimentary record with historical earthquake data
11:10-11:13 M. Moorkamp Integrated geophysical analysis of the April 2017 Moiyabana intra-plate earthquake, Botswana

TEXT-BASED EGU CHAT (11:15-12:30)
11:15-11:20 E. Gracia Earthquake crisis unveils the growth of an incipient continental fault system
11:20-11:25 O. Olesen Large magnitude earthquakes of late Holocene age in the Precambrian of Finnmark, Northern Norway
11:25-11:30 J. Ritz The Mw4.9 Le Teil surface-rupturing earthquake in southern France: New insight on seismic hazard assessment in stable continental regions
11:30-11:35 A. Vallage Full characterization of the ML 5.4 2019/11/11 Le Teil earthquake in France based on a multi-technology approach
11:35-11:40 T. King The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake
11:40-11:45 C.-H. Tsai Palaeo-earthquake magnitudes on the Dzhungarian fault, N. Tien shan, and implications for the rupture processes of intraplate strike-slip faults
11:45-11:50 H. Choi What if a larger earthquake would occur at the causative fault of the Gyeongju earthquake with ML 5.8 on September 11, 2016 in South Korea?
11:50-11:55 J. Kley Seismotectonic regions for Germany - Concept and results
11:55-12:00 D. Clark Neotectonic constraint on models of strain localisation within Australian Stable Continental Region (SCR) crust
12:05-12:10 C. Daxer Quantitative paleoseismology in Carinthia, Eastern Alps: Calibrating the lacustrine sedimentary record with historical earthquake data
12:10:12:15 R. Minetto High-resolution catalog of the the Maurienne Swarm (French Alps) based on template matching and double-different relocation
12:15-12:20 M. Moorkamp Integrated geophysical analysis of the April 2017 Moiyabana intra-plate earthquake, Botswana
12:20-12:25 C. Reyes-Carmona Evidence of recent activity in the Camorro Fault (Central Betics, Southern Spain)

12:25-12:30 - Additional questions and time for discussion

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Co-organized by NH4/TS5
Convener: Pierre Arroucau | Co-conveners: Beau WhitneyECSECS, Susana Custódio, Stéphane Baize, Ryan Gold, Dan Clark, Gordana Vlahovic, Sierd Cloetingh
Displays
| Attendance Fri, 08 May, 10:45–12:30 (CEST)

Files for download

Session materials Session summary Download all presentations (135MB)

Chat time: Friday, 8 May 2020, 10:45–12:30

D1387 |
EGU2020-3125<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
| solicited
| Highlight
Eulàlia Gràcia, Ingo Grevemeyer, Rafael Bartolomé, Héctor Perea, Sara Martínez-Loriente, Laura Gómez de la Peña, Antonio Villaseñor, Yann Klinger, Claudio Lo Iacono, Susana Diez, Alcinoe Calahorrano, Miquel Camafort, Sergio Costa, Elia d'Acremont, Alain Rabaute, and César R. Ranero

Large continental faults extend for thousands of kilometres and often form the tectonic boundaries between plates that are associated with prominent topographic features. In these active areas, well-defined faults produce large earthquakes, and thus imply a high seismic hazard. These paradigms are called into question in the Alboran Sea, which hosts an allegedly complex diffuse boundary between the Eurasia and Nubia plates, and we discovered one of the few examples worldwide of the initial stages of these key tectonic structures. On the 25th January 2016, a magnitude Mw6.4 submarine earthquake struck the north of the Moroccan coast, the largest event ever recorded in the Alboran Sea. The quake was preceded by an earthquake of magnitude Mw5.1 and was followed by numerous aftershocks whose locations mainly migrated to the south. The mainshock nucleated at a releasing bend of the poorly known Al-Idrissi Fault System (AIFS). According to slip inversion and aftershock distribution, we assume a rupture length of 18 km. Here we combine newly acquired multi-scale bathymetric and marine seismic reflection data with a resolution comparable to the studies on land, together with seismological data of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event recorded in the area – to unveil the 3D geometry of the AIFS. We found that, despite its subdued relief, the AIFS is a crustal-scale boundary. We report evidence of left-lateral strike-slip displacement, characterize their fault segments and demonstrate that the AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake and previous events of 1994 and 2004 supports that the AIFS is currently growing through propagation and linkage of its segments, which eventually might generate a greater rupture (up to Mw 7.6), increasing the potential hazard of the structure. The AIFS provides a unique model of the inception and growth of a young plate boundary system in the Alboran Sea (Western Mediterranean).

This work has been recently published in Nature Communications (IF:12.35), 10, 3482 (2019) doi:10.1038/s41467-019-11064-5. I would like to present our article recently published in NCOMM, so, please consider our work for an ORAL INVITED presentation. Many thanks!

How to cite: Gràcia, E., Grevemeyer, I., Bartolomé, R., Perea, H., Martínez-Loriente, S., Gómez de la Peña, L., Villaseñor, A., Klinger, Y., Lo Iacono, C., Diez, S., Calahorrano, A., Camafort, M., Costa, S., d'Acremont, E., Rabaute, A., and Ranero, C. R.: Earthquake crisis unveils the growth of an incipient continental fault system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3125, https://doi.org/10.5194/egusphere-egu2020-3125, 2020

D1388 |
EGU2020-21749<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Odleiv Olesen, Lars Olsen, Steven Gibbons, Tormod Kværna, Bent Ole Ruud, and Tor Arne Johansen

The 80 km long Stuoragurra postglacial fault occurs within the c. 5 km wide Precambrian Mironjavri-Sværholt Fault Zone in the northern Fennoscandian Shield. Deep seismic profiling and drilling show that the fault dips at an angle of 30-40° to the southeast. The reverse fault can be traced down to a depth of c. 2.5 km on the reflection seismic profile. A total of c. 100 earthquakes has been registered along the fault between 1991 and 2019. Recordings at the ARCES seismic array in Karasjok c. 40 km to the SE of the fault and other seismic stations in northern Norway and Finland have been utilized. The maximum moment magnitude is 4.0. The Stuoragurra fault constitutes the Norwegian part of the larger Lapland province of postglacial faults extending southwards into northern Finland and northern Sweden. The formation of these faults has previously been associated with the deglaciation of the last inland ice. Trenching of different sections of the fault and radiocarbon dating of buried and deformed organic material reveal, however, a late Holocene age (between c. 700 and 4000 years before present at three separate fault segments). The reverse displacement of c. 9 m and segment lengths of 9-12 km of the two southernmost fault segments indicate a moment magnitude of c. 7. The results from this study indicate that the maximum magnitude of future earthquakes in Fennoscandia can be significantly larger than the existing estimate of c. 6.

How to cite: Olesen, O., Olsen, L., Gibbons, S., Kværna, T., Ruud, B. O., and Johansen, T. A.: Large magnitude earthquakes of late Holocene age in the Precambrian of Finnmark, Northern Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21749, https://doi.org/10.5194/egusphere-egu2020-21749, 2020

D1389 |
EGU2020-8505<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Juliette Grosset, Stéphane Mazzotti, Philippe Vernant, Jean Chéry, and Kevin Manchuel

The Western Alps represent the zone of highest seismicity density in metropolitan France. The seismicity is mainly located along two NE-SW strike-slip fault systems: the right-lateral Belledonne Fault and the left-lateral Durance Fault. Glacial Isostatic Adjustment (GIA) is one of the most common processes given to explain intraplate seismicity (e.g., Scandinavia, North America) and is also proposed as a cause of present-day deformation in the Alps. In order to test the impact of deglaciation from the Last Glacial Maximum on pre-existing vertical strike-slip faults in the Western Alps (Belledonne and Durance Faults), we use a finite-element approach to model fault reactivation throughout the deglaciation period, from ca. 18 kyr up to today. The models are tuned to fit present-day deformation rates observed by geodesy (uplift rate up to 2 mm/yr and horizontal radial extension). Simplified models (homogeneous icecap and Earth rheology) show that, under optimum conditions, GIA stress perturbations can activate a NE-SW right-lateral strike-slip fault such as the Belledonne Fault, requiring the fault to have been pre-stressed up to near-failure equilibrium before the onset of deglaciation. The maximum effect of GIA is 1.7 meters of right-lateral slip over 20 kyr, with a peak of displacement between 20 and 10 ka. These models indicate that GIA can result in a maximum slip rate of 0.08 mm/yr averaged over the Holocene, in association with earthquakes up to Mw = 7 (if all displacement is taken in one event). These results are consistent with local paleoseismicity and geomorphology evidence on the Durance fault. However, the impact of GIA on the left-lateral Belledonne Fault is poorly constrained by these simple models. Additional models based on realistic Alpine icecap reconstructions and regional rheology structures will also be presented, that allow us to test the specific effects of GIA on Holocene deformation along both the Belledone and Durance Fault systems.

How to cite: Grosset, J., Mazzotti, S., Vernant, P., Chéry, J., and Manchuel, K.: Strike-slip fault reactivation in the Western Alps due to Glacial Isostatic Adjustment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8505, https://doi.org/10.5194/egusphere-egu2020-8505, 2020

D1390 |
EGU2020-8409<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
| Highlight
Jean-François Ritz, Stéphane Baize, Matthieu Ferry, Christophe Larroque, Laurence Audin, Bertrand Delouis, and Emmanuel Mathot

On November 11th 2019, a Mw 4.9 earthquake shook the Rhone River Valley in southern France, a rather densely populated area with many industrial facilities including several nuclear power plants. The “Le Teil” earthquake was felt as far as Montpellier and Grenoble, 120 km from the epicenter. Seismological data promptly showed that the earthquake corresponded to a reverse faulting event along a NE-SW trending fault with a focus at a very shallow depth (~1 km). In parallel, satellite-based radar observations (InSAR) showed the uplift of the SE compartment (up to 10 centimeters) along a sharp NE-SW trending ~4.5-km-long discontinuity. Field investigations conducted in the following days and weeks in the epicentral area uncovered several evidences of surface ruptures across roads and paths where the InSAR discontinuity is mapped. We also carried out airborne LiDAR surveys to map the rupture below the dense forest cover. Characteristics of surface deformations are fully consistent with InSAR and seismological data, and allow concluding to the reactivation of an Oligocene normal fault segment (i.e. La Rouvière fault) that belongs to the Cévennes fault system, a 120 km long polyphased system bounding the southern rim of the Massif Central. The absence of clear cumulative compressional deformation along the fault rupture, which on the contrary displays inherited extensional deformation (most likely Oligocene in age), suggests that the fault has not moved significantly since millions of years. These observations relaunch the question of seismic hazard assessment in stable continental regions such as continental France and most of Western Europe, where strain rates are very low.

How to cite: Ritz, J.-F., Baize, S., Ferry, M., Larroque, C., Audin, L., Delouis, B., and Mathot, E.: The Mw4.9 Le Teil surface-rupturing earthquake in southern France: New insight on seismic hazard assessment in stable continental regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8409, https://doi.org/10.5194/egusphere-egu2020-8409, 2020

D1391 |
EGU2020-9785<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
| Highlight
Amaury Vallage, Laurent Bollinger, Yoann Cano, Johann Champenois, Clara Duverger, Bruno Hernandez, Pascal Herry, Alexis Le Pichon, Constantino Listowski, Gilles Mazet-Roux, Marine Menager, Sophie Merrer, Béatrice Pinel-Puyssegur, Roxanne Rusch, Olivier Sèbe, Julien Vergoz, and Aurélie Guilhem Trilla

Metropolitan France is a region of slow tectonic deformation rates with sparse historical and instrumental seismicity, and where geodesy is not able to reach the required resolution in order to resolve the tectonic loadings. The few faults recognized as potential active rely on rare neotectonic slip rates, often integrated over geological scales.

In this context, the ML 5.4 Le Teil 2019 earthquake is of particular interest because it is the largest seismic event recorded in metropolitan France in the last 16 years. The last regional earthquake with a larger magnitude was the Lambesc event that occurred in 1909 about 110 km away from Le Teil epicenter. This recent earthquake offers a noteworthy opportunity to combine different technologies: seismological observations (RESIF and CEA) with satellite InSAR data and infrasound measurements, to help characterizing this stable continental region.

The analysis shows that the focal mechanism determined from the full waveform inversion of long-period seismological data is consistent with the activation of a reverse fault with a strike around 45°N and is associated with a moment magnitude of 4.8. Moreover, this event produced infrasound signals recorded by the OHP Alpine array located 110 km away. The analysis of these signals provides evidence of ground-to-air coupling in the epicentral region as well as ground shaking information.

Despite the moderate magnitude of the event, the ground deformation is resolved by InSAR with Sentinel-1 data. The interferogram is consistent with the shallow depth inverted from seismology and confirmed by the presence of surface ruptures. The inversion of multiple InSAR tracks allows characterizing the displacement at depth and along strike on the fault plane. The results are consistent with the focal mechanism derived from seismology. The earthquake has ruptured a 5-km long by ~1.5-km deep fault. The displacement reaches a maximum at a shallow 1 km-depth. The source inverted from InSAR coincides with the Rouvière fault, a branch of the Cévennes fault system formerly known as a normal fault. This reverse earthquake might be an example of an inherited structure re-activation as it is often the case in intraplate regions with polyphased history.

How to cite: Vallage, A., Bollinger, L., Cano, Y., Champenois, J., Duverger, C., Hernandez, B., Herry, P., Le Pichon, A., Listowski, C., Mazet-Roux, G., Menager, M., Merrer, S., Pinel-Puyssegur, B., Rusch, R., Sèbe, O., Vergoz, J., and Guilhem Trilla, A.: Full characterization of the ML 5.4 2019/11/11 Le Teil earthquake in France based on a multi-technology approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9785, https://doi.org/10.5194/egusphere-egu2020-9785, 2020

D1392 |
EGU2020-12723<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Mark Quigley, Tamarah King, and Dan Clark

The 20th May 2016 moment magnitude (MW) 6.1 Petermann earthquake was the 2nd longest single-event historic Australian surface rupture (21 km) and largest MW on-shore earthquake in 28 years. Trench logs from two hand-dug trenches show no evidence of penultimate rupture of surface eolian sediments or underlying calcrete. Available dating of eolian dunes 140 to 500 km away from the Petermann fault indicated eolian deposition during either the last glacial maximum (approximately 20 ka) or a period of aridification at approximately 180 - 200 ka. Ten 10Be cosmogenic nuclide erosion rates of bedrock outcrops at 0 to 50 km from the surface rupture trace are within error of each other between 1.4 to 2.6 mMyr-1. These samples have approximate averaging times between 208 to 419 ka. Bedrock erosion rates, trenching results and interpretation of the landscape history suggest the 2016 event is the only surface rupturing earthquake on the Petermann fault in the last 200 to 400 kyrs, and possibly the first ever on this fault. This finding is consistent with a lack of evidence for penultimate rupture for all eleven historic Australian surface rupturing events, as described by either trenching and/or landscape analysis and bedrock erosion rates. These ‘one-off’ events within Precambrian cratonic Australian crust are not consistent with trenching results and geomorphology of paleo-scarps within the Flinders Ranges and Eastern Australia which indicate multiple recurrent fault offset. Variable fault recurrence behaviour highlights that uniform seismic hazard modelling approaches are not applicable across Stable Continental Regions.

How to cite: Quigley, M., King, T., and Clark, D.: The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12723, https://doi.org/10.5194/egusphere-egu2020-12723, 2020

D1393 |
EGU2020-10030<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Mian Liu, Yuxuan Chen, Seth Stein, Gang Luo, and Hui Wang

Intracontinental earthquakes show complex spatiotemporal patterns. In North China, no large (M>7) earthquakes ruptured the same fault segments in the past 2000 years; instead they roamed among widespread fault systems. In Australia, morphogenic evidence indicates clusters of earthquakes separated by tens of thousands of years of dormancy. In central and eastern United States, paleoseismic studies suggest that large Holocene earthquakes occurred in places that are seismically inactive today. Such seismicity does not fit existing earthquake models that assume steady tectonic loading and cyclic stress release on fault planes. Intracontinental fault systems are widespread and collectively accommodate slow tectonic loading. A major fault rupture both transfers stress to the neighboring faults and perturbs loading conditions on distant faults. Thus, the loading rate on each individual fault can be variable. Slow tectonic loading means that local stress variations from fault interaction or nontectonic processes, or changes of fault strength, could trigger an earthquake. Furthermore, large intracontinental earthquakes usually rupture multiple fault segments or faults, which vary for each event. For these earthquakes, commonly used concepts such as recurrence intervals and characteristic earthquakes, all based on earthquake models assuming cyclic elastic rebound, are inadequate or inapplicable. On the other hand, the general patterns of intracontinental earthquakes can be described by the theory of complex dynamic systems, in which all faults interact with each other. The rupture of individual fault or fault segment cannot be predetermined, but the system behavior can be studied based on the records of previous events. We found that large intracontinental earthquakes, either on a fault system or in a region, are usually clustered and separated by long but variable periods of quiescence. The lengths of the quiescence periods inversely correlate with tectonic loading rates, and the characteristics of earthquake clusters depend on fault geometry and crustal rheology, through fault interaction and viscoelastic relaxation. Spatially, large intracontinental earthquakes are not limited to faults that are active recently, although weak regions tend to have more earthquakes. Intracontinental earthquakes require a different approach, one that focuses on stress interactions between faults in a complex dynamic system rather than stress accumulation and release on individual faults.

How to cite: Liu, M., Chen, Y., Stein, S., Luo, G., and Wang, H.: Complex spatiotemporal patterns of intracontinental earthquakes: a different game, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10030, https://doi.org/10.5194/egusphere-egu2020-10030, 2020

D1394 |
EGU2020-2539<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Chunyan Qu and Xin Qiao

The left-lateral strike-slip Haiyuan fault system is a major boundary fault zone on the northeast margin of the Qinghai -Tibet Plateau,separating active Tibet block and stable Alaxan & rdos blocks, and accommodating the eastward motion of Tibet Plateau. It consists of several sections, including Lenglongling segment (LLL), the Jinqianghe segment (JQH), the Maomaoshan segment (MMS), the Laohushan segment (LHS) and the rupture of the Haiyuan earthquake in 1920 from the west to the east. In 1920, a M8.5 Haiyuan earthquake occurred in the eastern segment of the fault zone, resulting in a surface rupture zone of about 240 km, with a maximum left-lateral coseismic displacement of 10 m. In the past 100 years after the earthquake, Haiyan fault is in a state of calm, no destructive earthquake of M 6.0 or above occurred. It is worth studying that how the fault activity and seismic hazard of each section of Haiyuan fault zone are at present.

We use geodetic data (High density InSAR and wide scale GPS) to study the present slip rate and locking degree of Haiyuan fault zone. we first use the Envisat/ASAR long-strip data of five tracks and the PSInSAR time series processing technology based on high coherence point target to obtain the average deformation rate field of the fault system during 2003~2010, and transform the deformation rate from line-of-sight (LOS) direction to the parallel fault direction. Then,we use two-dimensional screw dislocation model to fit the cross-fault deformation rate profiles, and obtain the fault kinematic parameters such as the fault slip rate and the locking depth. At the same time, we adopt the three-dimensional block model to invert the distribution characteristics of fault locking degree and slip rate deficit along the Haiyuan fault zone. We compare the difference of inversion results of different data individually and jointly, including large-scale sparse GPS data, high-density InSAR data and the combination of them. Finally we get the continuous strain accumulation state of the fault zone. The results show that from west to east, the slip rate decreases gradually, while the locking depth changes along the fault. The Laohushan section shows shallow surface creep. The analysis of the high-density cross-fault deformation rate profile of the Laohushan segment indicates that the creep length is about 19 km. Other segments in a locked state. But in the middle of the 1920 erathquake fracture section, the locking degree is weaker and shallower than other segments. These results are helpful to understand the present activity and assess regional seismic risk of Haiyuan fault zone.

How to cite: Qu, C. and Qiao, X.: Joint inversion of InSAR and GPS for fine slip rate and locking degree distribution along the Haiyuan fault zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2539, https://doi.org/10.5194/egusphere-egu2020-2539, 2020

D1395 |
EGU2020-710<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Chia-Hsin Tsai, Richard Walker, Simon Daout, Kanatbek Abdrakhmatov, Aidyn Mukambayev, Christoph Grützner, and Ed Rhodes

Long-term and present-day crustal deformation in the northern Tien Shan is poorly known, but is a key to understanding the mode of lithospheric deformation deep within the continental interiors, as well as the hazards posed by the slow-moving intraplate faults. Driven by the India-Asia collision, the NW-SE strike-slip faults and the E-W range-front thrust faults in the interior of Tien Shan together accommodate about 15-20 mm/yr of shortening. Here we focus on the NW-SE striking Dzhungarian fault (DZF) and the E-W striking Lepsy fault (LPF), which are large oblique strike-slip faults bounding the Dzhungarian Alatau, northern Tien Shan. Two large historical earthquakes in ~1716 and 1812 (Mw 8) were recorded in this region, and clear fault traces as well as scarps are visible from satellite images along some of the main faults. However, their geometries, slip rates, mode of deformation, expected earthquake magnitudes and recurrence interval have not been studied in details. A previous study suggested that the LPF ruptured in a seismic event around 400 yrBP that might be the 1716 earthquake known from historical records. Offsets of over 15 m were found over a fault length of 120 km, indicating a magnitude in the range Mw 7.5-8.2. The slip to length ratio for the LPF is unusally high, suggesting either that faults in this region are capable of generating very large earthquakes for a given fault length, or that the rupture length is underestimated.

Using a combination of high-resolution digital elevation models (DEMs) and orthophotos from High Mountain Asia (NASA), Pleiades optical imagery (CNES), drone photos and multi-temporal interferometric synthetic-aperture radar (InSAR) from the Sentinel-1 satellites, we identify the geomorphic signatures and quantify the long-term and short-term strain accumulation along the faults. The ~400 km DZF shows evidence for relatively ‘fresh’ rupturing along much of its length. We calculate an average lateral slip per event of 9.9 m from offset stacking analysis, which underlines the potential future large earthquakes on this fault. The proximity of the DZF and LPF ruptures and equivalent level of preservation opens the possibility that they were formed in a single earthquake event, with a moment-magnitude greater than 8. We also present estimates of long-term and short-term rates of slip across the DZF in order to estimate average recurrence intervals and to build a kinematic model of the faulting in the Northern Tien Shan.

How to cite: Tsai, C.-H., Walker, R., Daout, S., Abdrakhmatov, K., Mukambayev, A., Grützner, C., and Rhodes, E.: Palaeo-earthquake magnitudes on the Dzhungarian fault, N. Tien shan, and implications for the rupture processes of intraplate strike-slip faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-710, https://doi.org/10.5194/egusphere-egu2020-710, 2019

D1396 |
EGU2020-12276<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Guangyin Xu, Qing Wu, and Suyun Wang

The Ngari area in Tibet is in the forefront of land-continent collisions. The area is accompanied by the polymerization of plates, forming complex structures such as the Tethys Himalayan pleat belt, the Yarlung Zangbo suture belt, and the Gangdese continental margin magma arc from the south to the north. The multi-period dive collision-inland convergence process, the geological structure is complex and the seismicity is very high. Based on the Chinese historical earthquake catalogue, the China Modern Earthquake Catalogue and the seismic data from the International Seismological Center (ISC), we analyzed the seismic activity, focal mechanism and modern tectonic stress field in the Ngari area, and then analyzed the seismicity and its source of geodynamics. The main conclusions are as follows:(1) The seismic activities in the Ngari area are mainly distributed in the Himalayan tectonic belt, the Bangong-Nujiang tectonic belt, the Alkin-East Kunlun tectonic belt, and some near north-south trending tectonic belts; (2) Earthquakes near the Himalayan tectonic belt is dominated by reverse faulting events. The seismic activity near the Bangong-Nujiang tectonic belt and the Alkin-East Kunlun tectonic belt is dominated by strike-slip earthquakes. Near the north-south extensional tectonic belt, the earthquakes show as the normal faulting events. (3) The main direction of the modern tectonic stress field in the study area is near north-south direction; (4) Seismic activity, focal mechanism and modern tectonic stress field show that the geodynamic source in the Ngari region is from Collision and squeezing the between the Eurasian plate and the Indian Ocean plate.

How to cite: Xu, G., Wu, Q., and Wang, S.: Study on Seismicity and Its Geodynamic Genesis in Ngari Areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12276, https://doi.org/10.5194/egusphere-egu2020-12276, 2020

D1397 |
EGU2020-2788<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Peng Guo, Zhujun Han, Fan Gao, Chuanhua Zhu, and Hailong Gai

The rupture patterns of large earthquakes in transpressional systems can provide important information for understanding oblique motion and strain partitioning between tectonic blocks. The 1927 M8.0 Gulang earthquake occurred on the transpressional boundary between the Tibetan and Gobi-Alashan blocks. Combined with the results of previous studies, we find that the Lenglongling fault (LLLF) and Southern Wuwei Basin fault (SWBF) might have both ruptured during the Gulang earthquake, but they exhibited different motions. A ~120-km-long surface rupture zone formed along the LLLF, with a left-lateral strike-slip motion and a coseismic offset of ~2.4-7.5 m. Bending, bifurcation, and change of the slip sense occurs at both ends of the fault. The ~42-km-long rupture zone on the SWBF, with a coseismic vertical offset of ~0.6-2.8 m, can be divided into two segments. The eastern segment shows thrust motion, while the western shows thrust motion with a left-lateral strike-slip component. Thus, the Gulang earthquake may be a multifault rupture event where strike-slip and thrust faults ruptured simultaneously. Analysis of deep and shallow structures and three-dimensional finite-element modeling reveal that the north-dipping LLLF and the SWBF may converge downward to a low-angle decollement. This pattern of deformation partitioning is similar to some other earthquakes where oblique block convergence is partitioned into strike-slip motion on steeply dipping faults and vertical motion on gently dipping faults.

How to cite: Guo, P., Han, Z., Gao, F., Zhu, C., and Gai, H.: New insights into the complex surface faulting of the 1927 M8.0 Gulang earthquake, NE Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2788, https://doi.org/10.5194/egusphere-egu2020-2788, 2020

D1398 |
EGU2020-2119<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Sung-Ja Choi, Jinhyuk Choi, Kyoungtae Ko, Yirang Jang, and Jeong-Heong Choi

The Korean Peninsula is more than 400 km away from passive plate margins and considered a stable continent region. However, it has suffered from damaging earthquakes in the last 20 years. There are two major North–North East tectonic faults in the region: the Chugaryong fault running from Wonsan through Seoul to the west coast and the Yangsan fault in the southeastern part of the peninsula. The Yangsan fault extends for over 170 km and has been active since the late Cretaceous period. The fault has experienced many earthquakes in the last 2000 years, most recently  Mw 5.5 earthquake in its vicinity without any surface rupture. The fault has been studied by various disciplines, such as structural geology to determine the characteristics of the fault, geophysical exploration to determine the extension of the fault, and mineralogy to analyze fault gouges.[A1]  However, the last fault movement remains unknown. Trench studies on the Yangsan Fault undertaken in the central south of the Yangsan Fault to obtain its last movement revealed that the fault had been reactivated at least twice during the Holocene period, at approximately 2 ka and 4 ka. Before the Holocene, another fault movement occurred at approximately 50 ka, with a strike-slip motion creating a meter-wide fault damage zone. LIDAR and aerial photographs demonstrated that a higher terrace younger than 320 ka had moved by 1.5 km with a left-lateral-strike-slip motion. We now surmise that the Yangsan Fault has been continuously reactivated for more than 60 million years, and could potentially generate severe geohazards in the near future. Furthermore, even if the fault is inside an intraplate, we propose that it has continuously been reactivated from the Late Cretaceous to the present by plate tectonics.

How to cite: Choi, S.-J., Choi, J., Ko, K., Jang, Y., and Choi, J.-H.: Did the Yangsan Fault in a stable continent region move continuously during the Holocene?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2119, https://doi.org/10.5194/egusphere-egu2020-2119, 2020

D1399 |
EGU2020-2257<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Hoseon Choi

A seismic source can be a capable tectonic source or a seismogenic source. A capable tectonic source is a tectonic structure that can generate both vibratory ground motion and tectonic surface deformation at or near the earth's surface in the present seismotectonic regime. On the other hand, A seismogenic source generates vibratory ground motion but is assumed to not cause surface displacement, covering wide range of seismotectonic conditions, from a well-defined tectonic structure to simply a large region of diffuse seismicity.

The ML 5.8 Gyeongju earthquake on September 11, 2016 in South Korea is the largest instrumental one since 1978 that occurred in buried fault not exposed to the surface area. So to speak, there is no evidence of surface faulting till now. On the other hand, the geometry of the causative fault of the Gyeongju earthquake was revealed in detail from the distribution of foreshocks and aftershocks. Therefore, the causative fault of the Gyeongju earthquake can be treated as a seismogenic source corresponding to a well-defined tectonic structure as mentioned above.

What level of ground motions would occur at the site of interest if a larger earthquake would occur at the causative fault of the Gyeongju earthquake? To make a rough estimate of that question, we carried out a simple study of modeling the causative fault with the data available, and simulating strong ground motions with the stochastic and empirical Green’s function techniques. The magnitude of the maximum earthquake potential on the causative fault is in the range of 6.0 to 7.0 and increased by 0.5. We do not claim the possibility of such a large earthquake in the region, but have a goal to evaluate the seismic safety evaluation of the site of interest from such an earthquake potential. This type of study may help us elucidate the seismic hazard in a low seismicity area such as South Korea and review the seismic safety of the site of interest.

How to cite: Choi, H.: What if a larger earthquake would occur at the causative fault of the Gyeongju earthquake with ML 5.8 on September 11, 2016 in South Korea?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2257, https://doi.org/10.5194/egusphere-egu2020-2257, 2020

D1400 |
EGU2020-15231<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Tim Hahn, Jonas Kley, Diethelm Kaiser, Thomas Spies, Jörg Schlittenhardt, and Claudia Geisler

Seismotectonic regions are a basic input in seismic hazard assessment. Several seismotectonic regionalizations for Germany were proposed in the past. We are presently developing a new regionalization based on the definition in the Safety Standard of the Nuclear Safety Standards Commission KTA 2201.1 (2011-11): “A seismotectonic unit is a region for which uniformity is assumed regarding seismic activity, geological structure and development and, in particular, regarding neotectonic conditions. A seismotectonic unit may also be an earthquake source region.” Our new concept focusses on a transparent implementation of the required geological criteria. Our approach is to initially analyze those separately from present-day seismicity. Compared to existing source area models we strive for a better documentation and justification of the geological elements used to delimit seismotectonic regions. This includes an analysis of the geological history of structures in six time slices from the Permian to the Present that will be considered in the regionalization. The time slices are (1) Permian, (2) Triassic, (3) Jurassic to Early Cretaceous, (4) Late Cretaceous, (5) Cenozoic > 20 Ma and (6) Recent (< 20 Ma). They were chosen because they are separated by marked changes of stress and kinematic regimes and were associated with the evolution of new fault systems or reactivation of existing ones. The tectonic characteristics of the time slices are briefly described.

The present-day observable fault network comprises faults from all time slices. For each time slice, a subset of active faults will be extracted based on geological evidence for fault activity at that time, e.g. syntectonic deposits. The uncertainties of these age assignments will be documented. The fault subset will be used to estimate overall kinematics, a paleo-stress field and to delimit little deformed or stable areas. Faults, kinematics, stress and stable areas can then be compared to present-day seismicity/active faults, slip directions, stress and undeformed areas as well as other parameters such as crustal and lithospheric thickness. These steps are repeated for each time slice. The superposition of active faults and stable regions across all time slices will identify faults prone to reactivation and regions that remained undeformed over geological time, potentially indicating areas of increased or reduced present-day seismic hazard.

A comparison with seismicity of the last 1000 years shows partial agreement between regions of strong (or repeated) deformation and regions of higher seismicity. On the other hand, stronger earthquakes occasionally cluster in regions appearing stable since Permian time, the Anglo-Brabant Massif being a prominent example of this type.

How to cite: Hahn, T., Kley, J., Kaiser, D., Spies, T., Schlittenhardt, J., and Geisler, C.: Seismotectonic regions for Germany - Concept and results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15231, https://doi.org/10.5194/egusphere-egu2020-15231, 2020

D1401 |
EGU2020-6187<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Klaus Reicherter, Stephane Baize, Jochen Hürtgen, Francesca Cinti, Tom K. Rockwell, Herve Jomard, Gordon Seitz, and Joachim Ritter

Paleoseismic data on the eastern central Rhine Graben Boundary Fault, as part of the Upper Rhine Graben (URG) fault system, revealed Holocene earthquake activity with surface rupturing faults. The URG is one of the most seismically active areas in the stable continental interiors of Central Europe north of the Alps. We opened the first paleoseismic trenches N of Basel and S of Frankfurt along the ca. 300 km long eastern Rhine Graben Boundary Fault (RGBF). After extensive shallow geophysical and morphotectonic investigations and analyses, we discovered that the eastern central RGBF consists of several parallel fault strands that are marked by topographic steps, by varying hydrogeologic conditions, moisture content and by geophysical anomalies in the subsurface (GPR and ERT data). Some of the scarps close to the alluvial plain of the river Rhine have been identified as erosional features. We opened six trenches perpendicular and parallel to the second topographic scarp and strand of the main RGBF in Ettlingen area. Trenching the main RGBF was precluded due to forest cover and the presence of big blocks of rock in the colluvium at the base of the slope (red Triassic sandstones). Trenches were up to 20 m in length and 2 m in width, and up to 3 m in depth. None of the trenches reached the Triassic Buntsandstein “basement”, and all exposed Pleistocene and Holocene strata. Some strata are interpreted as blocky/gravelly colluvium of the Glacial periods, Loess, redeposited gleyey Loess, soli-/gelifluction layers and deposits and organic paleosols. Most of these layers are clearly displaced by faults and downthrown to the west, although some strata appear to warp or fold over faults. Massive liquefaction and periglacial features have been found, the relation to the sedimentary sequences in the trenches need to be elaborated in future. The process is interpreted to be instantaneous, as massive colluvium is placed against clayey/silty Loess deposits, and therefore we attribute these displacements to earthquake-related faulting. Creep along the strand can be ruled out. The displacement on free faces is on the order of 30 – 50 cm per event vertically, and considerable horizontal offset (ca. 2 m), and we found evidence for two of such events. Applying the commonly used empirical relationships, these findings are interpreted as two events with a magnitude M larger than 6. These results show the bias between the seismogenic landforms (scarps, hanging valleys, triangular facets, etc.) in the eastern UGR margin and seismicity recorded by seismic stations in the area, as currently most of the activity is found in the southern URG near Freiburg. Our findings contribute significantly to the completeness of the earthquake history in the eastern central URG.

How to cite: Reicherter, K., Baize, S., Hürtgen, J., Cinti, F., Rockwell, T. K., Jomard, H., Seitz, G., and Ritter, J.: Paleoseismological trenching of the eastern Rhine Graben Boundary Fault: the Ettlingen segment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6187, https://doi.org/10.5194/egusphere-egu2020-6187, 2020

D1402 |
EGU2020-19871<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Elizabeth H. Madden, Alice-Agnes Gabriel, Lucas Barros, Juraci Carvalho, and George França

Mitigating intraplate earthquakes is necessary, as local populations are at risk both directly from strong shaking and indirectly from the threat to public infrastructure such as dams. However, the infrequency of these events and insufficient knowledge of how the ground will respond to passing seismic waves challenges mitigation. In Brazil, one M 5 earthquake occurs about every 5 years. M 4 earthquakes are more common and produce shaking intensities up to VI and VII on the Modified Mercalli scale. Brazilian earthquakes are shallower on average than events in other intraplate regions, which raises the possibility that fault mechanics and earthquake dynamics are different here. To work toward improving hazard mitigation and to better understand the physics of earthquakes in Brazil, we present 3D numerical models of the rupture process of two recent earthquakes using the open-source dynamic rupture and wave propagation software, SeisSol (www.seissol.org). Typically, sparse data prohibits the modeling of intraplate events. However, the 2010 Mara Rosa earthquake, the largest earthquake ever recorded in the Goiás-Tocantins Seismic Zone in central Brazil, and the 2017 Maranhão earthquake, which occurred in a previously aseismic region of northern Brazil, are relatively well studied and ample data is available. We report results within the range of uncertainty from the uncertainty in observations of stress drop, epicentral depth, fault geometry and regional stress state. The Mara Rosa earthquake occurred at an epicentral depth of ~2 km, while the Maranhão earthquake occurred between ~12-16 km depth. Modeling these two events allows us to contrast the influence of depth on the modeled earthquake source characteristics. We propose that fault cohesion dominates fault strength for the shallowest intraplate events, assuming a typical Mohr-Coulomb relationship.

How to cite: Madden, E. H., Gabriel, A.-A., Barros, L., Carvalho, J., and França, G.: Rupture dynamics and fault mechanics of intraplate earthquakes in Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19871, https://doi.org/10.5194/egusphere-egu2020-19871, 2020

D1403 |
EGU2020-6279<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Daniel Clark

The mechanisms that lead to the localisation of stable continental region (SCR) seismicity, and strain more generally, remain poorly understood. Recent work has emphasised correlations between the historical record of earthquake epicentres and lateral changes in the thickness, composition and/or viscosity (thermal state) of the lithospheric mantle, as inferred from seismic velocity/attenuation constraints. Fluid flow and the distribution of heat production within the crust have also been cited as controls on the location of contemporary seismicity. The plate margin-centric hypothesis that the loading rate of crustal faults can been understood in terms of the strain rate of the underlying lithospheric mantle has been challenged in that a space-geodetic strain signal is yet to be measured in many SCRs. Alternatives involving the release of elastic energy from a pre-stressed lithosphere have been proposed.

The Australian SCR crust preserves a rich but largely unexplored record of seismogenic crustal deformation spanning a time period much greater than that provided by the historical record of seismicity. Variations in the distribution, cumulative displacement, and recurrence characteristics of neotectonic faults provide important constraint for models of strain localisation mechanisms within SCR crust, with global application. This paper presents two endmember case studies that illustrate the variation in deformation characteristics encountered within Australian SCR crust, and which demonstrate the range and nature of the constraint that might be imposed on models describing crustal deformation and seismic hazard.

The ~0.5 m high 2018 MW 5.3 Lake Muir earthquake scarp in southwest Western Australia is representative of a class of ruptures in the Precambrian SCR of Australia where the scarps are isolated from neighbouring scarps and there is little or no landscape evidence for recurrence of morphotectonic earthquakes, or of the construction of regional tectonic relief. In contrast, scarps in the Phanerozoic SCR of eastern Australia typically occur within a scarp-length of neighbouring scarps, and demonstrate extended histories of recurrence of morphotectonic events. For example, the ~75 km-long Lake George fault scarp is associated with a vertical displacement of ~250 m which accrued as the result of many morphotectonic earthquakes over the last ca. 4 Myr. The scarp links into neighbouring scarps, forming a belt-like arrangement that defines the topographic crest of the southeast Australian highlands. The limited data available indicates that recurrence is highly episodic, with periods of fault activity potentially coinciding with changes at the plate boundaries.

How to cite: Clark, D.: Neotectonic constraint on models of strain localisation within Australian Stable Continental Region (SCR) crust, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6279, https://doi.org/10.5194/egusphere-egu2020-6279, 2020

D1404 |
EGU2020-7327<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
| Highlight
Stephane Mazzotti, Juliette Grosset, Christine Masson, and Philippe Vernant

We constrain present-day deformation rates and styles in metropolitan France and neighboring Western Europe using a dataset of ca. 1200 GNSS horizontal and vertical velocities from continuous and semi-continuous stations. The characterization and correction of network-scale common-mode noise, combined with two independent network analysis technics allow the resolution of very small horizontal velocities (resp. strain rates) with a 95% confidence ca. 0.1–0.2 mm/yr (resp. ca. 1 x 10-9 yr-9) on a spatial scale of 100–200 km. The resulting velocity and strain rate fields show regional coherent patterns that can be associated with features that have been previously identified (e.g., orogen-normal extension in the Pyrenees and Western Alps), but also with new deformation patterns such as North-South shortening in northeastern France - southwestern Germany north of the Alpine Front (Vosges - Rhine Graben - Black Forest). A joint analysis of these new geodetic data with seismicity and focal mechanism catalogs allows the definition of regional seismo-tectonic models that can be compared with the numerous models of deformation processes proposed for Western Europe, from plate tectonics to erosion or Glacial Isostatic Adjustment. We show that plate and micro-plate tectonics play a minor (probably negligible) role in present-day deformation in metropolitan France and that alternative non-tectonic processes must be considered to better understand the origin of recent moderate earthquakes such as the March 2019 Ml=4.9 Montendre earthquake in the Aquitaine Basin or the Nov. 2019 Mw=4.8 Teil earthquake in the Rhone Valley.

How to cite: Mazzotti, S., Grosset, J., Masson, C., and Vernant, P.: Geodetic deformation rates and driving processes in metropolitan France and neighboring Western Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7327, https://doi.org/10.5194/egusphere-egu2020-7327, 2020

D1405 |
EGU2020-20740<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Estelle Hannouz, Christian Sue, Stéphane Baize, Jean-François Ritz, Matthieu Ferry, Laurence Audin, Andy Combey, Christophe Larroque, Andrea Walpersdorf, and Anne Lemoine

The Mw 4.9 earthquake that occurred near Montelimar on November 11, 2019 showed peculiar characteristics: a very shallow hypocenter (1km depth) with unexpected surface ruptures for such a moderate magnitude, and only few aftershocks showing low magnitudes (ML < 2.7). This event occurred in the industrialized Rhone Valley (including nuclear power plants and chemical industry) where several historical earthquakes with similar intensities and magnitudes took place (e.g. 1773, 1873, 1934).

The earthquake broke a ~5-km-long segment of the northern tip of the Cevennes fault system (La Rouvière Fault Segment). This ~100 km-long fault network has a NE-SW orientation trend and is inherited from the Variscan orogeny (~300 Ma). It first registered an extensive and transtensive tectonic phase ending at the Oligocene age (~30 Ma) before being inverted, as revealed by the reverse focal mechanism of the Le Teil event.

To date, this fault network has been poorly investigated in terms of seismic hazard, likely due to the low Mw expected on such short structures. Therefore, we started a new study to document its paleo-earthquake record in the framework of the new French RGF program (Alps and surrounding basins, BRGM).

Our first target was to map the cumulative trace of the fault. A first airborne LiDAR survey was acquired by helicopter and UAV (unmanned aerial vehicle) just after the earthquake. They allowed the identification of a continuous inherited scarp of 1 – 2 m in height over ~4 km along the preexisting Oligocene fault. In order characterize the post-Oligocene deformation along this fault, we performed a detailed analysis of geomorphological field observations, as well as a geophysical study by acquisition of seismic, electrical and ground-penetrating radar profiles. These profiles aimed to better understand how the 11/11/19 earthquake surface rupture is connected at depth to the Oligocene structure (La Rouvière Fault).

Each step of the analysis aims at eventually locating sites for further paleoseismological trenches, accounting for fault location, sediment preservation with favorable age determination potential and accessibility. This kind of investigation will provide information on the evolution over time of the seismic activity of this fault network, as well as relevant data on the current hazard they present in the specific context of the French Rhone Valley.

How to cite: Hannouz, E., Sue, C., Baize, S., Ritz, J.-F., Ferry, M., Audin, L., Combey, A., Larroque, C., Walpersdorf, A., and Lemoine, A.: Geomorphology of the cumulative deformation since Oligocene age on the Mw 4.9 Le Teil earthquake fault (South of France,11/11/19), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20740, https://doi.org/10.5194/egusphere-egu2020-20740, 2020

D1406 |
EGU2020-10802<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Christoph Daxer, Christa Hammerl, Maria del Puy Papi-Isaba, Stefano Claudio Fabbri, Patrick Oswald, Jyh-Jaan Steven Huang, Michael Strasser, and Jasper Moernaut

In intraplate settings with moderate seismicity, recurrence intervals of strong earthquakes (Mw >6) typically exceed the short time span of instrumental and historical records. To assess the seismic hazard in such regions, lake sediments are increasingly used as earthquake archives: they can record strong seismic shaking as mass transport deposits (MTDs), turbidites or sediment deformations, preserved over several thousands of years. To provide information on paleo-earthquake size, however, the sedimentary imprints need to be thoroughly calibrated with independent information on seismic shaking strength.

In Carinthia (Eastern Alps, Austria), numerous lakes have experienced several devastating historical earthquakes with local seismic intensities (SI) ranging from V-XI (EMS-98 scale), although being located in an intraplate environment. Given that i) these events are well-spaced in time (AD1201, AD1348, AD1511, AD1690, AD1857 and AD1976), ii) due to historical earthquake research, an exceptional historical documentation exists, and iii) accurate shakemaps can be built based on a local Intensity Prediction Equation (IPE), we can examine the relationship between seismic intensity and the type, size and spatial distribution of sedimentary imprint in the lakes.

Here, we present investigations on two large lakes – Wörthersee and Millstätter See – by a dense grid of reflection seismic profiles (~640 km overall), 80 short (~1.5 m) sediment cores and multibeam bathymetry. The lakes consist of several sub-basins with potentially different intensity thresholds for the generation of sedimentary imprints. Mapping of MTDs, their scarps and associated turbidites as well as accurate dating (radiocarbon and varve counting on sediment thin sections) shows that the AD1348 earthquake (Mw ~7) led to extensive slope failures in both lakes. The AD1511 (Mw ~6.9) and AD1690 (Mw ~6.5) events, which exhibited lower local intensities (~VII) compared to those of AD1348 (VIII), are recorded as minor MTDs and turbidites. Quantitative description of earthquake-related event deposits (cumulative turbidite thickness, volume of mass transport deposits/megaturbidites) suggests a linear correlation with the respective local intensities in both Wörthersee and Millstätter See.

The AD1976 earthquake (Mw ~6.5; SI V-VI at the lakes) is not evidenced in the sedimentary record and therefore can be used for constraining the minimum threshold intensity for seismically-induced event deposits. By applying a grid-search approach using an empirical intensity-attenuation relationship, we can narrow down possible earthquake scenarios. Our data suggests that the highly debated epicentre of the AD1348 earthquake was much closer to the Austrian-Italian border than the epicentre of the AD1976 Friuli earthquake, possibly originating from the Periadriatic lineament. The AD1511 event probably had its epicentre southeast of our study area in Slovenia, and therefore further east than previous studies suggested. The AD1690 earthquake, however, is most likely of a local origin.

Our study reveals that investigating one lake, let alone one sediment core, is insufficient to reconstruct a region’s seismic history. Due to the exceptional setting of Carinthia, however, we can constrain the intensity pattern and localise the most likely epicentral region and fault source of past earthquakes. In an ongoing interdisciplinary study, we use this calibration to construct long calibrated lacustrine records for the last 14 ka.

How to cite: Daxer, C., Hammerl, C., del Puy Papi-Isaba, M., Fabbri, S. C., Oswald, P., Huang, J.-J. S., Strasser, M., and Moernaut, J.: Quantitative paleoseismology in Carinthia, Eastern Alps: Calibrating the lacustrine sedimentary record with historical earthquake data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10802, https://doi.org/10.5194/egusphere-egu2020-10802, 2020

D1407 |
EGU2020-13302<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Riccardo Minetto, Agnès Helmstetter, Philippe Guéguen, Mickael Langlais, Olivier Coutant, Stéphane Schwartz, Gaël Janex, Jérôme Nomade, and Thierry Dumont

Since 2017, the Maurienne Valley (French Alps) has been affected by an episode of seismic unrest. In this study we focused on the seismic swarm that occurred in 2017 and 2018, which was characterized by 8 events with ML > 3 and a maximum magnitude of 3.7. The goal was to extend the existing SISmalp catalog, and also to provide accurate locations and magnitude estimations.

The employed data was recorded by a local seismic network composed of 6 broadband stations. The use of template matching allowed us to detect more than 70000 events, increasing the detection rate by more than ten times compared to the original catalog. We obtained high resolution locations applying a double difference relocation method, providing as input differential times calculated by cross-correlating templates with their respective detections. Finally, we estimated magnitudes using template-family-based linear regression analysis, in order to include even the weakest events. The seismic locations will be discussed in the tectonic and geological setting of the Maurienne Valley.

How to cite: Minetto, R., Helmstetter, A., Guéguen, P., Langlais, M., Coutant, O., Schwartz, S., Janex, G., Nomade, J., and Dumont, T.: High-resolution catalog of the the Maurienne Swarm (French Alps) based on template matching and double-different relocation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13302, https://doi.org/10.5194/egusphere-egu2020-13302, 2020

D1408 |
EGU2020-9241<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Max Moorkamp, Estella Atekwana, Islam Fadel, Alice-Agnes Gabriel, Folarin Kolawole, Elisha Shemang, Calistus Ramotoroko, Mark van der Meijde, Kevin Mickus, Ame Selepeng, and Loago Molwalefhe

The 3 April 2017 Moiyabana intra-plate earthquake in central Botswana occurred in a region that, until then, had been assumed to be seismically quiet. Its location away from the East African Rift system in a Proterozoic mobile belt between Archean Cratons has raised questions on the triggering mechanism and sparked various studies investigating the crustal and mantle structure in the region, the focal mechanism and the displacement associated with the event. Aeromagnetic and magnetotelluric data indicate movement on a NW striking and NE dipping fault. However, the details of the fault geometry differ when analysing each dataset independently. The geophysical inversion results plus reconstructions of fault movement from InSAR data are all compatible with normal movement and reactivation of a previous thrust fault. An open question though is to which degree fluids are responsible for triggering the event. Here we present first results of reconciling the different available datasets in an integrated analysis. We will show an updated geophysical model of the region around the hypocenter. Such a model can help to shed light on the rupture processes during the earthquake and forms a first step to unravel the genesis of this intra-plate event.

How to cite: Moorkamp, M., Atekwana, E., Fadel, I., Gabriel, A.-A., Kolawole, F., Shemang, E., Ramotoroko, C., van der Meijde, M., Mickus, K., Selepeng, A., and Molwalefhe, L.: Integrated geophysical analysis of the April 2017 Moiyabana intra-plate earthquake, Botswana, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9241, https://doi.org/10.5194/egusphere-egu2020-9241, 2020

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EGU2020-10595<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Miklos Kazmer, Nada Bushra El Tahir, Krzysztof Gaidzik, and Balázs Székely

The Nile is the longest river on earth, accordingly with huge drainage and major floods, regulated by the African monsoon. Significant amount of sediment is carried by the river; its deposition forms alluvial plains along most of its course. However, in Upper Egypt and northern Sudan there are six major and several minor cataracts totalling 327 km in length. There the river flows directly on bedrock, and a multitude of islands and rocks in the riverbed makes navigation hard or impossible throughout much of the year. Obviously, the Nile is unable to remove these obstacles from its flow (despite its ability to carve a deep canyon in the African continent during Messinian lowstand of the Mediterranean Sea). It has been suggested that the Cataract Nile is in a youthful stage, flows along structurally controlled turns and that earthquakes in southern Egypt prove that portions of the Nubian Swell are still tectonically active (Thurmond et al., 2004). However, the Sudan part of the river does not show any seismic activity. An archaeoseismological study is in progress to locate evidence of past earthquakes preserved in monumental architecture erected during the past 3500 years. Pyramids in Meroe display masonry shifted in plane of the wall: this was caused by one or more earthquakes of intensity I0 = 9 on the Archaeological Intensity Scale. We suggest that an ongoing systematic study of monumental stone and adobe buildings along the Nile in the region of the Nubian Swell will find further evidence of major earthquakes in the region, contributing to a better understanding of seismic hazard in Sudan.

Reference

Thurmond, A.K., Stern, R.J., Abselsalam, M.G., Nielsen, K.C., Abdeen, M.M., Hinz, E. (2004): The Nubian Swell. - Journal of African Earth Sciences 39, 401-407.

How to cite: Kazmer, M., El Tahir, N. B., Gaidzik, K., and Székely, B.: Is there active tectonics at the Nile cataracts in Sudan? An archaeoseismological study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10595, https://doi.org/10.5194/egusphere-egu2020-10595, 2020

D1410 |
EGU2020-19597<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Jorge P. Galve, Cristina Reyes-Carmona, Antonio Jabaloy, Patricia Ruano, José Vicente Pérez-Peña, José Miguel Azañón, and Guillermo Booth-Rea

The Camorro Fault is located at the foot of the northern slope of a limestone karstic massif that is called ‘Sierra de Las Chimeneas’, in the central sector of the Betic Cordillera (Southern Spain). The fault shows a well-marked surface expression. It is a 6 km-length strike-slip with extensional component fault that forms part of the Torcal Shear Zone. This fault can be continued 7 km eastward along the foot of northern slope of the ‘Torcal de Antequera’ (Málaga), World Heritage Site since 2016. The Camorro fault plane is well-exposed in some sectors while in others, the fault plane has been either affected by karstification processes or partially covered by talus deposits.

One of the most characteristic geomorphological features of the ‘Sierra de Las Chimeneas’ area is an impressive rock avalanche deposit, covering an area of 2.2 km2 and for which we estimated a volume of 0.48 Hm3. Given the characteristics of the rock avalanche deposit, we consider that it could be triggered by an earthquake on the Camorro Fault. This hypothesis is supported by other investigations that have already referred to quaternary paleoseismicity in this area. Previous archaeological research revealed a period of human occupation in a cave (‘Cueva del Toro’) located in the ‘Torcal de Antequera’ that point out evidences about the occurrence of a cataclysm in the late Copper Age (about 5000 years ago). Other studies have also suggested a possible connection between seismic events and megalith-building near Antequera. Beyond this, an archaeoseismic analysis in the megalithic site of Antequera (also World Heritage Site since 2016) found deformation structures probably linked to oscillations between the megalith orthostats during an earthquake. According to all of mentioned research, the Camorro Fault could be a good candidate to account for such prehistoric earthquake.

Further geochronological work remains to be done, specially focused on dating (e.g. by cosmogenic isotopes) the fault scarp of the Camorro Fault and the associated rock avalanche deposits. If cosmogenic and archaeological dates coincide, we could attribute all the mentioned observations to an earthquake of severe magnitude in an area where the population ignore that hazard. Thus, we could contribute not only to the history of human occupation of the World Heritage Site but also providing insights into the earthquake recurrence and seismic hazard of the region.

How to cite: Galve, J. P., Reyes-Carmona, C., Jabaloy, A., Ruano, P., Pérez-Peña, J. V., Azañón, J. M., and Booth-Rea, G.: Evidence of recent activity in the Camorro Fault (Central Betics, Southern Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19597, https://doi.org/10.5194/egusphere-egu2020-19597, 2020