Absolute stress levels on mature faults: Bridging insight from the lab and field using physics-based modeling
USGS | Earthquake Science Center Seminars
by Valere Lambert
3d ago
Valere Lambert Determining principles and conditions governing motion along faults is crucial for assessing how earthquake ruptures start and how large they may ultimately become. One of the most notable constraints for the stress levels along mature plate boundary faults is the abundance of evidence that the resistance to shear motion during substantial fault slip must be low (< 20 MPa). Two end-member hypotheses are used to explain such low-stress operation of mature faults: either (I) mature faults are strong at slow, quasi-static sliding rates but undergo considerable enhanced dynamic w ..read more
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Kinematic slip models of four large Intermountain West earthquakes of 2020 and 2021
USGS | Earthquake Science Center Seminars
by Fred Pollitz, USGS
2w ago
Fred Pollitz, USGS Four large earthquakes struck the Intermountain West and Basin and Range Province in 2020 and 2021: M5.7 March 18, 2020 Magna, Utah; M6.5 March 31, 2020, Stanley, Idaho; M6.5 May 15, 2020 Monte Cristo Range, Nevada; and M6.0 July 8, 2021 Antelope Valley, California, earthquake. As noted by Wesnousky (2020 SRL), each of the first three occurred in areas of relatively high background seismicity and geodetic strain rate; the same is true for the Antelope Valley earthquake. The events sample different tectonic environments with distinct fault geometries, leading to unique ruptur ..read more
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How Large Is the Spatial Area Influencing Site Response: Insights Gained from Multidimensional Analyses at the Treasure Island Downhole Array
USGS | Earthquake Science Center Seminars
by Mohamad Hallal, UC Berkeley
1M ago
Mohamad Hallal, UC Berkeley When attempting to model seismic site effects, most studies have focused on the importance of vertically characterizing subsurface geomaterials. However, laterally characterizing the geomaterials&#8217; variability has generally been either overlooked or oversimplified. As such, little is actually known about the spatial area that influences seismic site response. This presentation will share insights that have been gained regarding the spatial area that influences site response from performing two-dimensional (2D) ground response analyses (GRAs) for the Treasur ..read more
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Roles of Dynamic Rupture Simulations in the Development of Next Generation Probabilistic Fault Displacement Hazard Analysis (PFDHA) Models
USGS | Earthquake Science Center Seminars
by Yongfei Wang, SCEC
2M ago
Yongfei Wang, SCEC Coseismic fault displacements in large earthquakes have caused significant damage to structures and lifelines located on or near fault lines. For buildings or distributed infrastructure systems located near active faults, engineering displacement demands are defined using probabilistic fault-displacement hazard analysis (PFDHA) models. However, fault displacement models (FDMs) used in PFDHA are sparse and poorly constrained in part due to the scarcity of direct observations. The physics-based dynamic rupture simulation method is an attractive alternative to address this impo ..read more
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Subregional anelastic path effects in California
USGS | Earthquake Science Center Seminars
by Tristan Buckreis, UCLA
2M ago
Tristan Buckreis, UCLA Next Generation Attenuation (NGA) West2 ground motion models (GMMs) include regional path adjustments for broad geopolitical regions. We extend that framework to account for systematic variations in anelastic attenuation for nine physiographical subregions in California that are defined in consideration of geological conditions. Using a large database that is approximately doubled in size for California relative to NGA-West2, we find relatively fast attenuation in coast range areas (North Coast, Bay Area, Central Coast), relatively slow attenuation in eastern California ..read more
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Seismoelectric effects for subsurface characterization
USGS | Earthquake Science Center Seminars
by Christina Morency, Lawrence Livermore National Laboratory
3M ago
Christina Morency, Lawrence Livermore National Laboratory Classical approaches for Earth subsurface imaging rely predominantly on seismic techniques, which alone do not directly capture fluid-specific properties. On the other hand, electromagnetic (EM) measurements add constraints on the fluid phase through, for example, electrical conductivity. However, EM signals alone do not offer direct information of solid properties. In the recent years, there have been efforts to combine seismic and EM data for exploration geophysics. The most popular approach relies on joint inversion of decoupled seis ..read more
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Accessible and Multi-Lingual Earthquake Safety Messaging
USGS | Earthquake Science Center Seminars
by Mark Benthien, Earthquake Country Alliance
3M ago
Mark Benthien, Earthquake Country Alliance The Earthquake Country Alliance has created a variety of earthquake safety messaging documents in the top 16 languages spoken and read in California, at www.EarthquakeCountry.org/languages. Each document is also accessible for people who use screen reader technology. Funding for the ongoing project is provided to the California Governor&#8217;s Office of Emergency Services by FEMA (NEHRP) and subgranted to the Southern California Earthquake Center which administers ECA. This presentation will provide an overview of the process, lessons learned, an ..read more
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WaveDecompNet: a multi-task encoder-decoder network to separate earthquake and ambient noise signals in seismograms
USGS | Earthquake Science Center Seminars
by Jiuxun Yin, Caltech Seismological Laboratory
3M ago
Jiuxun Yin, Caltech Seismological Laboratory Seismograms contain multiple sources of seismic waves, from distinct transient signals such as earthquakes to continuous ambient seismic vibrations such as microseism. Ambient vibrations contaminate the earthquake signals, while the earthquake signals pollute the ambient noise's statistical properties necessary for ambient-noise seismology analysis. Separating ambient noise from earthquake signals would thus benefit multiple seismological analyses. This work develops a multi-task encoder-decoder network named WaveDecompNet to separate transient sign ..read more
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Advancing the Frontier of Subduction Zone (Earthquake) Science, by the USGS and its Partners
USGS | Earthquake Science Center Seminars
by Joan Gomberg, USGS
3M ago
Joan Gomberg, USGS Like many of its partners, the USGS has recognized the tremendous opportunity for advancing earthquake science that subduction zones (SZs) offer, because of 1) the extraordinary diversity of SZ earthquakes and other natural phenomena they initiate and respond to, 2) the new perspectives inspired by required multi-disciplinary and international work, and 3) technological advances enabling offshore exploration. Participation of USGS personnel in SZ-relevant partners&#8217; programs helps to ensure that the USGS fulfills its mandate to assess earthquake hazards and provide ..read more
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Fracture behavior at low effective stress
USGS | Earthquake Science Center Seminars
by Harry Lisabeth, Lawrence Berkeley National Laboratory
4M ago
Harry Lisabeth, Lawrence Berkeley National Laboratory The behavior of the upper crust is controlled in large part by fractures. Fractures are the conduits of fluid flow, facilitate reactions and transport of mass, and mediate deformation large and small. Fractures are not static features, but rather are sensitive to the hydraulic, chemical and mechanical environment in which they are set. I'll present the results of a multimodal experimental study of the physical properties of fluid-saturated, fractured rock in response to changes in fluid chemistry and stress. Complementary measurements were ..read more
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