TS5 – Earthquake Tectonics and Crustal Deformation
Paleoseismicity, active faulting, surface deformation, and the implications on seismic hazard assessment (Fault2SHA)
The study of active faults and deformation of the Earth's surface has made, and continues to make, significant contributions to our understanding of earthquakes and the assessment of seismic related hazard.
Active faulting may form and deform the Earth's surface so that records are documented in young sediments and in the landscape. Field studies of recent earthquake ruptures help not only constraining earthquake source parameters but also the identification of previously unknown active structures. The insights gleaned from recent earthquakes can be applied to study past earthquakes. Paleoseismology and related disciplines such as paleogeodesy and paleotsunami investigations still are the primary tools to establish earthquake records that are long enough to determine recurrence intervals and long-term deformation rates for active faults. Multidisciplinary data sets accumulated over the years have brought unprecedented constraints on the size and timing of past earthquakes, and allow deciphering shorter-term variations in fault slip rates or seismic activity rates, as well as the interaction of single faults within fault systems. Based on the this rich, but very heterogeneous knowledge of seismogenic faults, a variety of approaches have been developed to tranfer earthquake-fault geology into fault models suitable for probabilistic SHA. This session thus aims at linking field geologists, crustal deformation modellers, fault modellers, and seismic hazard practitioners.
In this session, we welcome contributions describing and critically discussing different approaches to study active faults. We are particularly interested in studies applying new and innovative methodological or multidisciplinary approaches. We hope to assemble a broad program bringing together studies dealing with on-land, lake or offshore environments, and applying a variety of methods such as traditional paleoseismic trenching, high-resolution coring, geophysical imaging, tectonic geomorphology, and remote sensing, as well as the application of earthquake geology in seismic hazard assessments. In addition, we encourage contributors describing how to translate fault data or catalogue data into fault models for SHA , and how to account for faults or catalogue issues.
Understanding fault growth and structural inheritance across spatial and temporal scales
The geometry and evolution of faults can be influenced by a range of different factors, including the presence of pre-existing structures or structural inheritance, over a range of spatial and temporal scales. Pre-existing structural heterogeneities, which are imparted through prior phases of deformation, are present across all scales throughout the lithosphere; from discrete fabrics at the centimetre scale to hundreds of kilometre scale rift systems and changes in lithospheric thickness. Fault growth can be controlled by factors including mechanical layering or variation, strain localisation, regional and local stress changes and reactivation of earlier structures – each of these factors are likely to influence the interaction between faults in a tectonic system. Therefore, by integrating our understanding of fault growth and interaction with respect to structural inheritance and ultimately earthquake hazard, over a range of spatial and temporal scales, will lead to greater understanding of the fundamental processes that govern fault behaviour.
Integrated approaches to bridge Long-term Tectonics and Earthquake cycles: Observations, Experiments, and Models
Our first-order understanding of earthquake cycles is limited by our ability to detect and interpret natural phenomena or their relict signatures on faults. However, such observations allow us to define fundamental hypotheses that can be tested by way of experiments and models, ultimately yielding deeper insights into mechanics of faulting in nature. Inter-, co-, and post-seismic deformation can be documented geodetically, but the sparseness of the data and its large spatial and temporal variability do not sufficiently resolve their driving mechanisms. Laboratory experiments under controlled conditions can narrow down the possibilities, while numerical modelling helps extrapolating these results back to natural conditions. Thus, integrated approaches to bridge long-term tectonics and the earthquake cycle that combine observation, interpretation, experimentation, and finally, physical or numerical modelling, are key for our understanding of the deformation behaviour of complex fault systems.
This session seeks contributions toward an integrated perspective on the earthquake cycle that span a wide range of observations, methodologies, and modelling over a variety of spatial and temporal scales. Presentations can cover brittle and ductile deformation, from microstructures to mantle rheology and with applications to earthquake mechanics, geodynamics, geodesy, geohazards, and more. Specific questions include: How do long-term crustal and lithospheric deformation affect short-term seismicity and earthquake cycle behaviour? What is the long-term topographic signature of the earthquake? What are the relative contributions of rheology and geometry for seismic and aseismic slip? What are the roles of on- and off-fault deformation in shaping the landscape and partitioning seismic and aseismic energy dissipation? We welcome submissions by early-career scientists in particular.
— Invited speaker: Luc L Lavier, Jackson School of Geosciences | The University of Texas at Austin
Earthquakes, active tectonics, and seismic hazard in regions of slow lithospheric deformation
Earthquakes that occur within regions of slow lithospheric deformation (low-strain regions) are inherently difficult to study. The long interval between earthquakes, coupled with natural and anthropogenic modification, limit preservation of paleoearthquakes in the landscape. Low deformation rates push the limits of modern geodetic observation techniques. The short instrumental record challenges extrapolation of small earthquake recurrence based on modern seismological measurement to characterize the probability of larger, more damaging earthquakes. Characterizing the earthquake cycle in low-strain settings is further compounded by temporal clustering of earthquakes, punctuated by long periods of quiescence (e.g. non-steady recurrence intervals). However, earthquakes in slowly deforming regions can reach high magnitudes and pose significant risk to populations.
This session seeks to integrate paleoseismic, geomorphic, geodetic, geophysical, and seismologic datasets to provide a comprehensive understanding of the earthquake cycle in low-strain regions. This session 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. 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.
Anatolia is characterized by well-defined boundaries such as the North and East Anatolian faults and relatively less known intra ‘plate’ structures. The relationship and relative importance of these two deformation regions, along the boundaries and within the interior of Anatolia, remains a matter of debate. This small piece of continental lithosphere is part of the Eastern Mediterranean, where broad scale tectonics are dominated by the interaction of the Nubian and Arabian plates with Eurasia. Anatolia is bounded by different tectonics regimes on all sides: continental convergence to the east, continental extension to the west, oceanic subduction further south and west in the Aeagan, and continental transform in the north. The evolution and present deformation of Anatolia are constrained by diverse geological, geophysical, and geodetic observations and have been explained by different hypotheses, such as (a) tectonic escape system caused by the post-collisional convergence of Eurasian and Arabian plates creating forces at its boundaries with gravitational potential differences of the Anatolian high plateau (b) asthenospheric flow dragging the circular flow of lithosphere from the Levant to Anatolia in the east and the Aegean in the west, (c) slab pull of the Hellenic subduction, (d) mantle upwelling underneath Afar and with the large-scale flow associated with a whole mantle, Tethyan convection cell, (e) or combinations of these mechanisms. Naturally, this setting generates frequent earthquakes with large magnitudes (M > 7), forming a natural laboratory on understanding the crustal deformation for various disciplines of active tectonics.
Multi-disciplinary studies, especially within the last three decades, have made great contributions to our understanding of the processes on the crustal deformation of Anatolia and the adjacent regions. With this session, we aim to bring together the recent findings of these studies, thus we welcome/invite contributions from a wide range of disciplines such as, but not limited to, neotectonics, seismology, tectonic geodesy (e.g. GNSS, InSAR), paleoseismology, tectonic geomorphology, remote sensing, structural geology and geodynamic modelling.
- A. M. Celâl Şengör (İstanbul Teknik Üniversitesi, email@example.com) - The Neotectonics of Turkey and its Aetiology
- Robert Reilinger (MIT, firstname.lastname@example.org) - Anatolia-Aegea at the junction of ocean subduction and continental collision
Understanding large subduction earthquakes and tsunamigenesis by integrating geological and geophysical observations, laboratory results, and numerical modeling
Since 2004, there have been a number of large subduction earthquakes whose unexpected rupture features contributed to the generation of devastating tsunamis. The impact that these events had on human society highlights the need to improve our knowledge of the key mechanisms behind their origin. Advances in these areas have led to progess in our understanding of the most important parameters affecting tsunamigenesis. For example, unexpectedly large slip was observed during the 2011 Tohoku-Oki earthquake, leading to re-investigations of the geology of other subduction zones and the conditions that can lead to large slip at the trench.
In general, the large amount of geophysical data recorded at present has led to new descriptions of faulting and rupture complexity (e.g., spatial and temporal seismic rupture heterogeneity, fault roughness, geometry and sediment type, interseismic coupling, etc.). Rock physicists have proposed new constitutive laws and parameters based on a new generation of laboratory experiments, which simulate close to natural seismic deformation conditions on natural fault samples. Analog modellers now have apparati that simulate multiple seismic cycles with unprecedented realism. These represent a valuable tool for investigating how various boundary conditions (e.g., frictional segmentation, interplate roughness) influence the seismic behavior of subduction megathrusts. In addition, advances in numerical modelling now allow scientists to test how new geophysical observations, e.g. from ocean drilling projects and laboratory analyses, influence subduction zone processes over a range of temporal and spatial scales (i.e., geodynamic, seismic cycling, earthquake rupture, wave propagation modelling).
In light of these advances, this session has a twofold mission: i) to integrate recent results from different fields to foster a comprehensive understanding of the key parameters controlling the physics of large subduction earthquakes over a range of spatial and temporal scales; ii) to individuate how the tsunami hazard analysis can benefit from using a multi-disciplinary approach.
We invite abstracts that enhance interdisciplinary collaboration and integrate observations, rock physics experiments, analog- and numerical modeling, and tsunami hazard.
The Mechanics of Faulting from shallow to deep earthquakes: Interplay between multiple length scales.
The mechanics of earthquakes is controlled by a spectrum of processes covering a wide range of length scales, from tens of kilometres down to few nanometres. For instance, while the geometry of the fault/fracture network and its physical properties control the global stress distribution and the propagation/arrest of the seismic rupture, earthquake nucleation and fault weakening is governed by frictional processes occurring within extremely localized sub-planar slipping zones. The co-seismic rheology of the slipping zones themselves depends on deformation mechanisms and dissipative processes active at the scale of the grain or asperity. If this is the case of shallow earthquakes, the nucleation of intermediate and deep earthquakes remains enigmatic since it occurs at elevated ambient pressure-temperature conditions which should favour plastic deformation and suppress frictional processes. Though, recent studies on fault rocks of Earth’s lower crust and upper mantle reveal microstructures comparable to those associated with co-seismic slip and off-fault damage in brittle rocks. The study of such complex multiscale systems requires an interdisciplinary approach spanning from structural geology to seismology, geophysics, petrology, rupture modelling and experimental rock deformation. In this session we aim to convene contributions dealing with different aspects of earthquake mechanics at various depths and scales such as:
· the thermo-hydro-mechanical processes associated to co-seismic fault weakening based on rock deformation experiments, numerical simulations and microstructural studies of fault rocks;
· the study of natural and experimental fault rocks to investigate the nucleation mechanisms of intermediate and deep earthquakes in comparison to their shallow counterparts;
· the elastic, frictional and transport properties of fault rocks from the field (geophysical and hydrogeological data) to the laboratory scale (petrophysical and rock deformation studies);
· the internal architecture of seismogenic fault zones from field structural survey and geophysical investigations (e.g. seismic, electric and electromagnetic methods);
· the modeling of earthquake ruptures, off-fault dynamic stress fields and long-term mechanical evolution of realistic fault networks;
· the earthquake source energy budget and partitioning between fracture, friction and elastic wave radiation from seismological, theoretical and field observations.
· the interplay between fault geometry and earthquake rupture characteristics (e.g. coseismic slip and rupture velocity distribution) from seismological, geodetic, remote sensed or field observations;
We particularly welcome novel observations or innovative approaches to the study of earthquake faulting. Contributions from early career scientists are solicited.
Solicited oral presentation: Matthew Tarling (University of Otago)
Earthquake foreshocks: identification, observation, modeling, and lessons to be learned
Over the past several years, interest in earthquake foreshocks has experienced considerable growth. This can, on one side, be explained by a largely improved observational database that spans all seismic scales. A development that is driven by a growing number of permanent seismic stations and large-scale campaign networks, the development of advanced detection and analysis techniques, and by the improvement of laboratory equipment and techniques. In addition, the ongoing endeavor to better understand induced seismicity has been contributing to this upgrowth with densely-monitored underground lab-scale experiments and enhanced microseismic monitoring. On the other side, earthquake foreshocks are widely perceived as one of the few and, as of now, most direct observations of earthquake nucleation processes.
Foreshocks are generally thought to arise by one of two mechanisms: cascading failure or preslip. The cascading model proposes that a mainshock following a foreshock has an identical origin to that of aftershocks. In this case, earthquake frequency-magnitude statistics predict that occasionally an aftershock will be larger than the prior event, which makes the prior event a foreshock only after the fact. The mechanism proposed by the preslip model is that premonitory processes - perhaps fault creep related to mainshock nucleation - result in stress changes that drive the foreshock process. Seismologists have found no agreement so far; this is made more difficult by two facts: that no agreed-upon, universal strategy to identify foreshocks in a seismic catalog exists and that data quality and quantity vary considerably over spatial and temporal scales.
In this session, we want to bring together scientists from all disciplines working on, or interested in, earthquake foreshock occurrence. We invite reports on observational and theoretical studies on all scales. This includes laboratory and deep underground experimental earthquakes, as well as microseismic to megathrust earthquakes. We also encourage submissions from colleagues working on advanced detection and analysis techniques for improved foreshock identification.
Earthquake Source Processes: Recent Advances in Observation, Imaging, and Modeling
This session covers the broad field of earthquake source processes, and includes the topics of observing the surface deformation caused by earthquakes, imaging the rupture kinematics and simulating earthquake dynamics using numerical methods, to develop a deeper understanding of earthquake source physics. We also invite presentation that link novel field observations and laboratory experiments to earthquake dynamics, and studies on earthquake scaling properties. Of particular interest are innovative studies on quantifying the uncertainties in earthquake source-parameter estimation.
Within this framework our session also provides a forum to discuss case studies of field observation, kinematic and dynamic source modeling of recent significant earthquakes.