US5

EDI
Faults, Rivers and Topography: in memory of Patience A. Cowie

Patience Cowie revolutionised our understanding of the growth and interaction of faults, and the impact these have on the topography of extensional settings. Through her tenacious focus on the science, infectious enthusiasm, wonderful sense of humour and commitment to women in science, she inspired a generation of young researchers, many of whom are presenting in this Union Symposium.
Patience’s early research began with the growth and interaction of faults and their length/displacement scaling. She studied faults at different scales, from small scale, linking damage zone to displacement, to whole fault systems, demonstrating how the development of complex fault networks impacts fault slip rate. She built numerical models of fault interactions that integrated the response of river systems to the changing topography. The predictions of these models challenged geomorphological and stratigraphic understanding of extensional settings, and resulted in a wealth of research on the extraction of tectonic signals from river profiles, and the sedimentological record of these processes.
This Union Symposium aims to sustain the momentum of Patience Cowie’s multidisciplinary approach to tackling fundamental questions concerning the interactions between the brittle upper crust and the surface processes that govern much of Earth’s topography. We are now addressing the physical mechanisms that can lead to the variety of slip styles and frictional behaviour on faults; this is critical to forecasting seismic hazard. As faults propagate, they determine the geometry of river networks, the distribution of erosion and the response time of river channels. These interactions govern sediment routing systems and the stratigraphic record of these processes. This symposium seeks to explore a future vision for the science underpinned by the fundamental processes linking faults and topography, balanced by an awareness of the societal challenges of risk management to natural hazards in these settings.

Convener: Hugh Sinclair | Co-conveners: Mikaël Attal, Anneleen Geurts, Laura Gregory
Presentations
| Wed, 21 Apr, 15:00–17:00 (CEST)

Presentations: Wed, 21 Apr

Chairperson: Hugh Sinclair
15:00–15:05
Speaker order (chair for introduction and questions, 12 minutes talk, 3 minutes questions)
Chair - Laura Gregory
15:05–15:20
|
EGU21-110
Christopher H. Scholz

Patience Cowie’s PhD thesis, conducted with me at Lamont, resulted in three papers, published in 1992, that laid the groundwork for the modern era of fault mechanics studies. In the first paper1 she reasoned that a cohesive zone model provided a plausible model of fault grown provided that the width of the cohesive zone scales linearly with fault length. In that case, the Griffith instability is avoided and faults grow self-similarly in quasistatic equilibrium. This model is consistent with the existence of faults of all sizes in which displacement scales linearly with length and the fault grows by the breakdown of a damage zone at the fault tip. In the second paper2 she showed that the then existing data for fault displacement and length were consistent with linear scaling for faults rupturing rock of similar strength. In the third paper3 she combined the earthquake slip/length scaling law with that fault scaling law to show how faults can grow by the accumulation of slip from earthquakes.

In the subsequent thirty years much more work has been done to expand on these themes pioneered by Patience. Here I share some memories of working with Patience in those formative years.

 

1          Cowie, P. A. & Scholz, C. H. Physical explanation for the displacement-length relationship of faults using a post-yield fracture mechanics model. J.       Struct. Geol. 14, 1133-1148 (1992).

2          Cowie, P. A. & Scholz, C. H. Displacement-length scaling relationship for faults: data synthesis and discussion. J. Struct. Geol. 14, 1149-1156 (1992).

3          Cowie, P. A., and Scholz, C.H. Growth of faults by accumulation of seismic slip. J. Geophys. Res. 97(B7), 11085-11095 (1992b).

How to cite: Scholz, C. H.: Patience Cowie and the Inception of Modern Fault Mechanics:  A Recollection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-110, https://doi.org/10.5194/egusphere-egu21-110, 2021.

15:20–15:45
|
EGU21-7780
Zoe Shipton

Patience Cowie was a truly outstanding scientist whose research spanned several disciplines of structural geology and tectonics. She made a lasting contribution to every discipline she published in and as well as academic advances, produced significant impacts in the hydrocarbon industry and earthquake hazard assessment. Her research in fault mechanics and fault population was a genuine game-changer. The implications of her work for predicting fault patterns and linkage have been crucial for the interpretation of 3D seismic data, and for examining the interplay between faults and the basins they bound and sediments they host. More recently she explored relationships between fault geometry, slip rate and recurrence intervals along seismically active faults, with important implications for earthquake hazard assessment.

Patience’s drive to constrain physical explanations of the underlying dynamics of Earth processes meant her numerical modelling was always firmly grounded in field observations. Her models incorporated the effects of stress in time and space as fault system evolved, but always underpinned by geometric and kinematic observations in the field. She loved fieldwork and her joy at the beauty of geological structures was infectious and inspiring.  

How to cite: Shipton, Z.: A retrospective of the work of Patience Cowie: the interaction of faults in space and time and their influences on subsurface fluid flow, surface processes and earthquakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7780, https://doi.org/10.5194/egusphere-egu21-7780, 2021.

Chair - Mikael Attal
15:45–16:00
|
EGU21-15774
Joanna Faure Walker, Francesco Iezzi, and Gerald Roberts

Changes in fault geometry, throw-rates and slip-rates along the length of a fault are crucial for understanding fault evolution and interaction and need to be incorporated in interpretation of fault scaling relationships and earthquake hazard assessments. Normal fault examples from Iceland and Italy provide examples of soft linkage, breach faults, and bends in faults that can be used to investigate fault growth at different stages of fault linkage. We find that at all stages of fault linkage studied, bends in strike along a fault affect throw-rate profiles along the fault. Crucially, for fault-based seismic hazard assessment, we need to consider how we interpret throw-rate and slip-rate profiles along a fault because how we interpret slip-rate profiles will impact moment release calculations and hence recurrence intervals. We therefore need detailed data regarding fault geometry and slip-rates to inform fault-based seismic hazard assessments, uncertainties and where further study is needed.

How to cite: Faure Walker, J., Iezzi, F., and Roberts, G.: Fault evolution, scaling relationships and hazard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15774, https://doi.org/10.5194/egusphere-egu21-15774, 2021.

16:00–16:15
Chair - Anneleen Geurts
16:15–16:30
|
EGU21-1179
Philippe Steer, Louise Jeandet-Ribes, Rodolphe Cattin, Martine Simoes, Nadaya Cubas, Harsha S. Bhat, J. Bruce H. Shyu, Maxime Mouyen, Odin Marc, and Niels Hovius

Tectonics, climate and surface processes dictate the evolution of Earth’s surface topography. Topographic change in turn influences lithospheric deformation, but the temporal and spatial scales at which this feedback can be effective remains an open issue. Here, we make a synthesis of recent developments investigating how erosion impacts the stress-loading of faults and potentially induces some earthquakes. We first show, using an elastic model for the lithosphere, that erosion rates of ca 0.1–20 mm.yr−1, as documented in active compressional orogens, can raise the Coulomb stress by ca 0.1–10 bar on the nearby thrust faults over an earthquake cycle, by changing both the normal and tangential stress. This model also suggests that short-lived but intense erosional events can represent a prominent mechanism for inter-seismic stress loading of faults near the surface. Indeed, we demonstrate that typhoon Morakot in 2009, which triggered numerous landslides, was followed by a step increase in the shallow (< 15 km depth) earthquake frequency and in the b-value, lasting at least 2.5 years. These observations suggest that the progressive removal of landslide debris by rivers from southern Taiwan has increased the crustal stress rate and earthquake activity. Last, we use QDYN, a quasi‐dynamic numerical model of earthquake cycles to investigate the effect of a large erosional event, such as typhoon Morakot, on seismicity. We show that erosional events with a duration shorter than the duration of an earthquake cycle can significantly increase the seismicity rate, even for small stress changes. Consistent with the increase in the b-value observed after typhoon Morakot, our results also show that large erosional events with a period similar to the earthquake nucleation timescale can change earthquake size distribution by triggering more small events. Overall, these modelling results and observations highlight that short-lived but intense erosional events can lead to perceptible changes in shallow seismicity, affecting both earthquake frequency and size-distributions.

How to cite: Steer, P., Jeandet-Ribes, L., Cattin, R., Simoes, M., Cubas, N., Bhat, H. S., Shyu, J. B. H., Mouyen, M., Marc, O., and Hovius, N.: Towards a better understanding of the impact of erosion on fault slip and seismicity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1179, https://doi.org/10.5194/egusphere-egu21-1179, 2021.

16:30–16:45
|
EGU21-1195
Sofia Pechlivanidou

The Corinth Rift, Greece, is a young (~5 Ma) sea-level controlled rift and one of the most rapidly extending areas on Earth. The unique combination of high strain and sedimentation rate with a closed drainage system and the well preserved syn-rift sedimentary record makes the Corinth Rift an ideal laboratory for understanding interactions between surface processes and tectonics and their implications for syn-rift stratigraphy.

The Corinth Rift has exceptional onshore and offshore field data coverage and as such it represents one of the best natural examples for model calibration. To this end, offshore sediment packages mapped from seismic reflection data were used to validate the surface process model pyBadlands, by comparing the total real and modeled sediment volumes and deposition patterns over the past 130 kyr.  Our results shed light on the impact of tectonic forcing on sediment fluxes by showing that sediment supply to the rift is not primarily controlled by relief development, but instead by tectonically-driven tilting of the landscape. This is the first time that this has been demonstrated for a natural system and challenges the view that relief is a key control on catchment averaged erosion rates.

Moreover, recent drilling data from IODP Expedition 381 in the Corinth Rift generated a complete record of the syn-rift sequence offshore and provided the first age constraints to enable us to resolve sediment accumulation rates with high temporal resolution. The new cores record climate-driven cyclic variations in the basin paleoenvironment, alternating between glacial/isolated and interglacial/marine periods. A key finding is that sedimentation rates are markedly increased during glacial/isolated periods. Furthermore, bed frequency and bed thicknesses show significant stratigraphic variability and highlight the dominance of gravity flow sedimentation which represents > 60% of the total sedimentation during the last glacial-interglacial cycle.

This extraordinary offshore drilling data when combined with surface processes modelling will provide an unprecedented opportunity to address the challenge of resolving tectonic versus climatic controls on sediment production and stratigraphic development within rift basins.

How to cite: Pechlivanidou, S.: From surface processes modelling to high-resolution drilling record: resolving key controls on sediment production and stratigraphic development in the Corinth Rift, Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1195, https://doi.org/10.5194/egusphere-egu21-1195, 2021.

16:45–17:00

Additional speakers/contributors without abstracts

  • Alex Whittaker, Imperial College London, United Kingdom