Unraveling Multi-Scale Fault Zone Behaviors with Small Earthquake Focal Mechanisms
USGS | Earthquake Science Center Seminars
by Yifang Cheng, Tongji University, Shanghai
4d ago
Yifang Cheng, Tongji University, Shanghai Earthquake focal mechanisms offer insights into the architecture, kinematics, and stress at depth within fault zones, providing observations that complement surface geodetic measurements and seismicity statistics. We have improved the traditional focal mechanism calculation method, HASH, through the incorporation of machine learning algorithms and relative earthquake radiation measurements (REFOC). Our improved approach has been applied to over 1.5 million catalog earthquakes in California from 1980 to 2021, yielding high-quality focal mechanisms for m ..read more
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Offshore Fault Damage and Slip Behavior: Insights from Microseismicity and Seismic Imaging
USGS | Earthquake Science Center Seminars
by Travis Alongi, U.S. Geological Survey
1w ago
Travis Alongi, U.S. Geological Survey Many of the world’s most damaging faults are offshore, presenting unique challenges and opportunities for studying earthquakes and faults. This talk explores how earthquake-generated (passive) and human-made (active) marine seismic methods improve our knowledge of on-fault slip behavior and off-fault damage. The first part of my talk explores coupling along the poorly resolved shallow offshore portion of the southernmost Cascadia subduction zone plate interface using microseismicity patterns. Knowledge of coupling provides information about the s ..read more
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Variable short-term slip rate on the Imperial fault modulated by filling of the Salton Trough by Lake Cahuilla
USGS | Earthquake Science Center Seminars
by Thomas Rockwell, San Diego State University
1w ago
Thomas Rockwell, San Diego State University The Salton Basin was free of significant water between about 100 BCE and 950 CE but has filled to the sill elevation of +13 m six times between ca 950 and 1730 CE. Based on a dense array of cone penetrometer (CPT) soundings across a small sag pond, the Imperial fault is interpreted to have experienced an increase in earthquake rate and accelerated slip in the few hundred years after re-inundation, an observation that is also seen on the southern San Andreas and San Jacinto faults. This regional basin-wide signal of transient accelerated slip in inter ..read more
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Mechanics of caldera collapse earthquakes and their seismic representations
USGS | Earthquake Science Center Seminars
by Taiyi Wang, Stanford University
3w ago
Taiyi Wang, Stanford University All instrumented basaltic caldera collapses generate Mw > 5 very long period earthquakes. However, previous studies of source dynamics have been limited to lumped models treating the caldera block as rigid, leaving open questions related to how ruptures initiate and propagate around the ring fault, and the seismic expressions of those rupture dynamics. In the first part of my talk, I will present the first 3D numerical model capturing the nucleation and propagation of ring fault rupture, the mechanical coupling to the underlying viscoelastic magma, and the as ..read more
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What does the 2024 M 7.5 Noto Hanto, Japan, quake tell us about short-term forecasting and long-term hazard?
USGS | Earthquake Science Center Seminars
by Shinji Toda, Tohoku University
1M ago
Shinji Toda, Tohoku University The 1 Jan 2024 Noto Hanto earthquake launched a plethora of ills on the Noto Hanto population, taking 200 lives, and causing $25B in damage, only $5B of which was insured. These ills include a tsunami that arrived within a few minutes of the mainshock, as well as unexpectedly strong shaking throughout the Noto peninsula. In addition to direct shaking damage, the shaking triggered massive landslides in steep terrain, and caused extensive liquefaction in coastal marshes and estuaries. Coastal uplift of up to 4 m also lifted fishing harbors out of the water. Because ..read more
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Tidally modulated icequake periodicity and its implication for rift zone dynamics
USGS | Earthquake Science Center Seminars
by Mong-Han Huang, University of Maryland
1M ago
Mong-Han Huang, University of Maryland The Ross Ice Shelf (RIS) in Antarctica is the largest ice shelf in the world. As the RIS flows toward the Ross Sea, a buildup of tensile stress due to increasing ice flow velocity develops a series of flow-perpendicular rift zones. Although these rifts are essential in contributing to future calving and reduction in size of the ice shelf, their material properties and mechanical response to external stress in the rift zone scale (~10-100 km) are poorly understood, partly due to a lack of high spatial-temporal scale in-situ observations to characterize key ..read more
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Adventures in Measuring Variations in High-Frequency Radiation for Small to Moderate Earthquakes
USGS | Earthquake Science Center Seminars
by Peter Shearer, University of California, San Diego
1M ago
Peter Shearer, University of California, San Diego Similar-sized earthquakes vary in the strength of their high-frequency radiation and various modeling assumptions can be used to translate these differences into stress-drop estimates. Empirical methods are widely applied to correct earthquake spectra for path effects in order to estimate corner frequencies and stress drops, but suffer from tradeoffs among model parameters that hamper estimates of absolute stress drop and comparisons between different studies or regions. Based on our recent work documenting hard-to-resolve tradeoffs between ab ..read more
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A decade of prospective evaluations of earthquake forecasting models in California: What have we learned and what can we do with it?
USGS | Earthquake Science Center Seminars
by Toño Bayona, University of Bristol
1M ago
Toño Bayona, University of Bristol The Collaboratory for the Study of Earthquake Predictability (CSEP) is a global community of scientists whose mission is to advance earthquake predictability research though the rigorous and prospective evaluation of probabilistic seismicity forecasts. One of CSEP’s major international achievements is the development and operation of dozens of time-varying and time-invariant seismicity models for California, including various versions of the well-established Epidemic-Type Aftershock Sequence (ETAS) and Short-Term Earthquake Probability (STEP) models ..read more
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Spatial correlation in ground motion intensities: Measurement, prediction, and seismic risk implications
USGS | Earthquake Science Center Seminars
by Jack W. Baker, Stanford University
1M ago
Jack W. Baker, Stanford University The amplitude of ground shaking during an earthquake varies spatially, due to location-to-location differences in source features, wave propagation, and site effects. These variations have important impacts on infrastructure systems and other distributed assets. This presentation will provide an overview of efforts to quantify spatial correlations in amplitudes, via observations from past earthquakes and numerical simulations. Regional risk analysis results will be presented to demonstrate the potential role of spatial correlations on impacts to the built env ..read more
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Probabilistic regional liquefaction hazard and risk analysis: A case study of residential buildings in Alameda, CA (In-person presentation)
USGS | Earthquake Science Center Seminars
by Emily Mongold, Stanford University
3M ago
Emily Mongold, Stanford University The impact of liquefaction on a regional scale is not well understood or modeled with traditional approaches. This paper presents a method to quantitatively assess liquefaction hazard and risk on a regional scale, accounting for uncertainties in soil properties, groundwater conditions, ground shaking parameters, and empirical liquefaction potential index (LPI) equations. The regional analysis is applied to a case study to calculate regional occurrence rates for the extent and severity of liquefaction and to quantify losses resulting from ground shaking and li ..read more
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