Earthquake Science Center Seminars

Kelian Dascher-Cousineau, University of California, Berkeley

Seismology is witnessing explosive growth in the diversity and scale of earthquake catalogs. A key motivation for this community effort is that more data should translate into better earthquake forecasts. In this presentation, I report on recent works in 1) improving aftershock forecasts, 2) investigating the seismic triggering potential of slow slip events, and 3) introducing deep learning methods for earthquake forecasting. Our results underscore the importance of large datasets in yielding robust earthquake forecasts. Furthermore, they illustrate how more data can unlock new, more flexible methodologies.

Christie Rowe, McGill University

Earthquake recurrence in time and space is recorded in the rock record (deep/ long term) and sedimentary record (shallow/recent). Mechanistic understandings of earthquakes have not so far made a major contribution to forecasting but this could represent an area of scientific potential growth. In this talk I will review recent progress on understanding controls on the earthquake cycle from structural studies in the rock record. I will focus on evidence for post-seismic healing mechanisms which offer an opportunity to relate fault strength evolution to timescales. I will explore implications and opportunities for better integrating structural geology and paleoseismology to understand earthquake recurrence.

Jessica Murray, U.S. Geological Survey

Chris Milliner, California Institute of Technology

Understanding the mechanics of faulting and accurately assessing seismic hazards are crucial for mitigating the impact of earthquakes. This seminar investigates the use of satellite pixel tracking data to unravel fundamental geomechanical properties of fault systems by providing novel estimates of friction, the absolute magnitude of stresses in the Earth's crust and evolution of inelastic strain as fault systems mature.

Here, I present a methodology based on Mohr-Coulomb failure theory with a quasi-static stress assumption to estimate fault friction parameters using satellite pixel tracking data. Applying this approach to the 2019 Ridgecrest earthquake sequence reveals statically strong and dynamically weakened friction, of 0.61 and 0.29, respectively, which are consistent with experimentally derived lab values. Additionally, I will argue that this approach can estimate the absolute magnitudes of stresses in the crust, shedding light on the driving forces behind earthquakes and their implications for future seismic activity.

In the second part of the seminar, I will present preliminary results of the friction analysis applied to the recent Mw 7.8 and Mw 7.6 Kahramanmaraş earthquakes in Türkiye. It is found that slip release along a specific fault segment deviates from the expected behavior under quasi-static stresses, suggesting an possible effect of strong dynamic stresses associated with rupture propagation.

Lastly, I will present estimates of surface deformation from radar and optical pixel tracking of 17 of the largest (6.0 ≤ Mw ≤ 7.9), historic, continental strike-slip surface ruptures to estimate the amount of inelastic coseismic off-fault strain. These results indicate progressively smaller amounts of off-fault inelastic strain with higher cumulative displacements, faster rupture velocities and geologic slip rates, supporting the notion that faults systems localize as they mature.

Karl Kappler, QuakeFinder

Short term (days to hours) earthquake forecasting is a hard scientific problem. Monitoring electromagnetic (EM) rather than mechanical/seismic activity may provide a breakthrough in this research. Anecdotal EM studies of single earthquakes lack of reproducible observations, and non-uniqueness of the anomalies when data are examined over the long term. However, in the early 2000s, a private humanitarian effort (QuakeFinder) was established to address the deficiency of data and to build out a dataset appropriate for statistical analysis. Three-component induction magnetometers were deployed at more than 100 stations running along the San Andreas and other major faults in California. More than 300,000 station days have been acquired with many stations nearby to significant earthquakes. The goal was to determine if there is a natural signal prior to moderate to large (>M4) earthquakes within range ( < 40 km) of the magnetometer instruments. Two major peer-reviewed statistical analyses (QuakeFinder and Google GAS) were done in 2019 and 2022. Both studies indicated rejection at the 99.7% confidence level of the null hypothesis (that there is not an electromagnetic precursor to earthquakes) at a baseline when crude noise compensation measures are applied. These statistical studies form the basis of further investigations, perhaps by USGS, to move the technology towards an operational, short term (days not seconds), earthquake warning system.

Rishav Mallick, California Institute of Technology

Viscoelastic processes in the upper mantle redistribute seismically generated stresses and modulate crustal deformation throughout the earthquake cycle. Geodetic observations of these motions at the surface of the crust-mantle system offer the possibility of constraining the rheology of the upper mantle. Parsimonious representations of viscoelastically modulated deformation through the aseismic phase of the earthquake cycle should simultaneously explain geodetic observations of (a) rapid postseismic deformation, (b) late in the earthquake cycle near-fault strain localization. To understand how rheological formulations affect kinematics, we solve a set of integral equations to simulate periodic earthquake cycles for a vertical strike-slip fault governed by rate-dependent friction in a homogeneous elastic crust underlain by a viscoelastic upper-mantle. We explore two popular viscoelastic rheological model classes in our simulations, linear Burgers and power-law rheologies; we show that these model classes are nearly kinematically indistinguishable with current geodetic observational techniques, though they may have different implications for stress transfer within the deforming medium. The degeneracy in predicted kinematics is broken when the system is perturbed by earthquake sequences i.e., aperiodic events with non-characteristic magnitudes. However, when the true rheology follows a power-law, estimating rheological parameters from earthquake sequence observations do not yield unique parameters. We discuss possible remedies and some issues related to non-steady state or transient rheologies. Distinguishing between linear, power-law and possibly transient rheologies and estimating associated parameters is a step towards building better regional seismic hazard models.

Itzhak Lior, The Hebrew University of Jerusalem

Distributed Acoustic Sensing (DAS) is revolutionizing observational seismology by allowing for seismic measurement every few meters along tens-of-kilometers long optical fibers. One application bearing immense scientific and societal implications is the use of DAS for Earthquake Early Warning (EEW). For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismic stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work we harness optical fiber infrastructure, ubiquitously deployed across the world both on-land and off-shore, for EEW. We devised methods for real-time magnitude estimation and ground motion prediction and validated them using earthquakes recorded in France, Greece and Chile. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes.

Associated publication: https://www.nature.com/articles/s41598-023-27444-3

Margaret Glasgow, U.S. Geological Survey

Fluid-injection induced seismicity has been ongoing for more than two decades in the Raton Basin, a coal-bed methane field located on the Colorado-New Mexico border. The uptick in seismicity began in 2001 approximately 10 years ahead of the central United States average. Sparse seismic instrumentation existed prior to 2015. Prior to denser instrumentation beginning in 2016, three broad zones of seismicity were identified. Each zone was suggested to host a 10-15 km long normal fault. However, denser instrumentation combined with the application of automated and machine learning methods reveal that the major zones of seismicity are composed of a series of short faults, ~1-3 km long. The faults have variable strikes and predominately normal slip. Unlike some regions of induced seismicity, the earthquake statistics (e.g., b-value, interevent time) for the Raton Basin are indistinguishable from those found in tectonic settings. Seismicity has greatly diminished in one of the three zones, the Trinidad zone, despite having hosted some of the largest earthquakes in the basin including a Mw 5.3 in 2011. We built an earthquake catalog for this zone from 2008-2022 that heavily relied on one legacy U.S. Transportable Array station. This time range includes multiple topics of interest – the lead up to the Mw 5.3 mainshock and the decline in seismicity beginning in ~2016. Unlike previous results which suggested the mainshock ruptured an anomalously long fault, ~10 km, and was low stress drop, we suggest the mainshock ruptured ~5.5 km and within an hour triggered seismicity up to ~5 km from the mainshock rupture. The recent decline in seismicity in the Trinidad zone is most likely predominately due to the 80% reduction in nearby wastewater injection but another contributor may be the diminished tectonic stress following the 2011 Mw 5.3 mainshock earthquake sequence. The Trinidad zone provides an opportunity to better understand this potentially inadvertent but seemingly effective mitigation.

Te Yang Yeh, San Diego State University

We have simulated 0–3 Hz deterministic wave propagation in the Southern California Earthquake Center Community Velocity Model (CVM) version CVM‐S4.26‐M01 for the 2019 Mw

Victor Tsai, Brown University

Why do earthquakes damage buildings? Many buildings are damaged most heavily by high-frequency ground motion rather than longer period shaking. Despite the importance of these high-frequency ground motions, there is little understanding of what causes them, with ground motion models accounting for them purely empirically. Moreover, most frictional models for earthquakes generally underpredict how strong such high-frequency ground motions are, even when heterogeneous friction and realistic roughness are accounted for. In this talk, I discuss the role of complex fault zones in generating high-frequency ground motions, with a focus on the potential role of collisions of structures as they attempt to slide past each other during an earthquake. Interestingly, the ground motion from collisions depends mostly on the size and shape of the structures and does not depend on the magnitude of stresses within the Earth and thus gives a very different interpretation of what causes the most damaging ground motions. When incorporated with standard frictional models, the collision model explains various observations that are otherwise difficult to explain, including why stress drops sometimes are not observed to be magnitude invariant, why fault zones with more complexity have stronger ground motions, and why high-frequency radiation patterns are more isotropic than can be explained by scattering.