Geophysics and Tectonics Seminar - fall-2024
Robotics for earthquake science: more data, new analyses
Oct. 16, 2024
noon - 1 p.m.
Geology 1712
Presented By:
- Dr. Zhiang Chen - Caltech
Subscribe to Calendar
Machine learning has revolutionized data processing, yet collecting large datasets for its application in earthquake science remains a challenge. This talk introduces the use of robotics to automate data collection, a crucial step toward automating and advancing geoscience research. I present three cases where integrating robotics and machine learning opens new avenues for fault zone characterization and fragile geological feature analysis. In bedrock fault zones, understanding the geometric distributions of rocks is essential for elucidating fault scarp formation and development processes. I have employed UAVs and deep-learning techniques for large-scale, high-resolution analysis of rocky fault scarps in the California Volcanic Tableland, enabling the detection and analysis of a large number of diverse rock geometries and distributions. Strong correlations between rock geometries and geomorphic features inform a particle transportation model, providing a new perspective that extends past research on macroscopic scarp geometry such as slope, height, and length. In new work, I am designing a multi-UAV system to autonomously collect and map millimeter-scale fracture data, offering rapid earthquake damage assessment. Following an earthquake, a scout UAV autonomously locates surface faulting perimeters, and a fleet of low-flying mapping UAVs captures high-resolution images, which are then analyzed by deep neural networks to extract detailed fracture geometry and surface deformation characteristics. Finally, for fragile geological features such as precariously balanced rocks (PBRs), I have developed methods using UAVs and deep learning for automated detection, mapping, and dynamic analysis. Utilizing a virtual shake robot powered by a physics engine, I analyze PBR overturning and large-displacement dynamics, providing ground motion constraints essential for earthquake studies. These advances illustrate how improved methods for dense data collection can provide new insights into earthquake surface rupture and ground motions, advancing our understanding of the impacts of earthquakes on the landscape.
Water in the Martian Crust
Oct. 23, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Prof. Vashan Wright - UCSD
Subscribe to Calendar
Liquid water existed on Mars in rivers, lakes, and as groundwater. The water is hypothesized to have subsequently been buried as ice or liquid water, incorporated in minerals, or lost to space. Geophysical measurements have the potential to test the first of these three hypotheses because water affects the physical properties of rocks, such as elastic moduli and bulk density. We use a forward modeling approach and a Markov Chain Monte Carlo inversion scheme to identify combinations of rock type, water distribution, porosity, and pore shape consistent with the seismic velocities and gravity within 50 km of the InSight lander on Mars. The shear Vs and compression Vp wave velocities within the upper 300 m are consistent with a crust composed of minimally cemented (< 2 % of the pores) sediments. Fractured rocks at this depth could host ice within 20% of the pore space. Vs within the upper 8 km of the crust are too low for a fully ice-saturated cryosphere. Using Vs, lithology, and gravity-derived bulk density data, we find that the lower crust (11.5-22 km below the surface) beneath InSight is mafic and highly porous or felsic and less porous. The addition of Vp data leads to the conclusion that a lower crust composed of igneous rock with thin fractures filled with liquid water can explain the existing data. Our results have implications for understanding Mars’ water cycle from the Noachian to the present, determining the fates of past surface water, searching for past or extant life, and assessing in-situ resource utilization for future missions.
Explore earthquake cycle behaviors using 3D numerical simulator
Oct. 30, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Dr. Qingjun Meng -
Subscribe to Calendar
Earthquake cycle simulation involves modeling earthquake nucleation, coseismic, postseismic and interseismic phases, and it could reveal more information about fault properties including friction parameters and effective normal stress distribution. I will present two case studies, one is for strike slip earthquakes and another of subduction zone events, utilizing a newly developed 3D finite element based earthquake cycle simulator EQdyna. (1) Large earthquakes frequently occur along the southern San Andreas fault (SSAF) with a quasi-periodic recurrence interval between about 116 and 221 years over the last millennia, except for the most recent long quiescence (>300 yrs). The SSAF locates beside ancient Lake Cahuilla that experiences periodic inundations and desiccations in historical time. Previous studies suggest a temporal correlation between Lake Cahuilla flooding and SSAF earthquakes, although a direct causal relationship is still in debate. Here we quantitatively explore the influence of hydrologic perturbations associated with Lake Cahuilla on the SSAF earthquakes. (2) Shallow slow slip events (SSEs) contribute to strain release near the shallow portions of subduction interfaces and may contribute to promoting shallow subduction earthquakes. However, shallow SSEs are difficult to be detected by on-shore geodetic and seismic networks. To complement recent efforts in off-shore monitoring of shallow SSEs, we use the earthquake simulator that captures both quasi-static and dynamic slip to explore the interactions between shallow SSEs and earthquakes
Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism
Nov. 6, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Prof. Bruce Buffett - UC Berkeley
Subscribe to Calendar
Fluctuations in the geomagnetic field occur over a broad range of timescales. Short-period fluctuations are called secular variation, whereas excursions and reversals are viewed as anomalous transient events. An open question is whether distinct mechanisms are required to account for these different forms of variability. We explore this question using trends b in the axial dipole moment from six time-dependent geomagnetic field models. Variability in b during times of stable polarity exhibits a predictable dependence on the time interval (or window) for the trend. The variance of b also reveals a simple relationship to trends during excursions and reversals. This connection hints at a link between reversals, excursions, and secular variation. We can quantitatively distinguish excursions, reversals, and secular variation solely on the basis of trend durations rather than differences in the underlying physical process. While this analysis does not rule out distinct physical mechanisms, the paleomagnetic observations suggest that such distinctions are not required.
Investigating Seismicity and Crustal Structures in Western Hispaniola Island (Haiti)
Nov. 13, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Hsin-Yu Lee - UC Riverside
Subscribe to Calendar
In 2010, a devastating M7.0 earthquake struck southern Haiti on a previously unmapped fault rather than the primary strike-slip fault, the Enriquillo-Plantain Garden Fault (EPGF), causing over 200,000 deaths and an estimated $8 billion in damages. About a decade later, another M7.2 earthquake in 2021 occurred approximately 100 kilometers west of the 2010 event, leading to more than 2,200 deaths and is thought to have ruptured structures north of the EPGF. Following the 2010 event, a temporary seismic network was deployed around the rupture area, and later, an N-S transect seismic array was set up from 2013 to 2014. Although primary results from previous studies identified the unmapped fault, seismicity observations have been limited by high noise levels. Taking advantages of these stations and prior result, we apply a template-matching technique to the 2010 and 2013-2014 seismic networks to further investigate microseismicity in the area. The spatiotemporal distribution of seismicity reveals three earthquake swarm instances, providing insights into potential triggering mechanisms. To further explore crustal structures, we also apply ambient noise tomography to the N-S transect array to obtain a 2-D shear wave velocity (Vs) model across Haiti. The velocity model shows patterns consistent with geologic units and reveals interior crustal structures which support geological interpretations of the area. The findings from these studies provide fundamental information and insights for seismic hazard assessment in this seismically active region.
The Multi-Faceted Seismicity Dynamics of the San Jacinto Fault Zone
Nov. 20, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Valeria Villa - Caltech
Subscribe to Calendar
The San Jacinto Fault Zone of the major San Andreas Fault Zone system holds seismological mysteries along its 210 km strike length. Researchers have long been perplexed by its high seismic rate, profuse deep microseismicity (15-22 km) below the geodetic locking depth, numerous seismic clusters, and rich production of moderate to large magnitude events. Here, we built a fifteen-year catalog (2008-2022) from deep learning algorithms and used probabilistic and statistical methods to identify the prolific seismicity and unearth the fault’s mechanisms. Our findings suggest that seismic activity along the fault is predominantly from non-interacting earthquakes occurring below the geodetic locking depth, possibly due to a highly heterogeneous broad transition zone. An exception is a complex faulting area known to produce moderate earthquakes, which our results showed to be an aftershock-prone area at any depth. A significant number of seismic clusters have been newly confirmed as swarms, shedding light on previously unexplored phenomena in seismic activity.
The Three-Body Problem: Supraglacial Lakes, the Greenland Ice Sheet, and Subglacial Sediments
Dec. 4, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Prof. Wenyuan Fan - UCSD
Subscribe to Calendar
Greenland ice flow is highly responsive to surface meltwater input into the subglacial hydrological system; however, the mechanisms controlling this relationship remain poorly constrained. Seasonal variations in ice velocity are most often explained by two non-exclusive hypotheses that make contradictory predictions for long-term ice sheet behavior in a warming climate: a self-regulating subglacial hydrological system or a sediment-controlled system with evolving till strength. We use integrated seismic and geodetic observations in western Greenland to test these hypotheses. Our findings show that the large influx of meltwater to the basal hydrologic system following a rapid supraglacial lake drainage weakens and mobilizes basal sediments, leading to an acceleration in ice flow and increased sensitivity to subsequent runoff variations. As the melt season ends, the sediment restrengthens, resulting in a reduction in ice velocity. Our results provide the first continuous, seasonal constraints on basal sediment control of ice sheet dynamics, offer new evidence for the role of supraglacial lake drainages in modifying basal sediment strength, and underscore the need for future research to better understand the distribution of subglacial sediments and the effects of predicted increases in runoff and lake expansion on future ice flow and sea level rise.