11/06/2018 - 12:00pm
Munk Conference Room
Knowledge of material and geometric properties along major faults in Southern California is critical for understanding the large earthquake potential and seismic hazard in the region. Using different signals and techniques, I image these properties at multiple length-scales (100 km to 100
m) with a focus on the two most seismically active faults in the area, the San Andreas (SAF) and San Jacinto (SJF) faults. Analysis of fault zone head waves reveals long (40-60 km), continuous segments of the central and northern SJF through Cajon Pass, and, the SAF northwest and southeast of San Gorgonio Pass (SGP) with across-fault VP contrasts of 3-11%. High-resolution travel-time tomography shows distinct along-fault changes in large-scale (>4 km) structure through SGP, potentially impeding large earthquakes propagating through the region. It also reveals a major northeast-dipping structure within the southern SAF system around Coachella Valley. Broad damage and deformation associated with the SJF and SAF manifest as high VP/VS anomalies at shallow depth (<5km) and in some areas at greater depth (>10 km) as low VP/VS anomalies. These variations give insight into the complex interplay between fault-associated damage, crack geometry, fluid content and lithology near these faults. At smaller scale (~100 m-1 km), the internal structure of the SJF is imaged using characteristics of earthquake waveforms, including arrival time variations and fault zone trapped waves recorded by dense linear arrays crossing the fault. These analyses reveal 100-200 m wide and <5 km deep core damage zones located predominantly northeast of the seismogenic SJF. The determined fault geometries, bimaterial structures, damage asymmetry and deformation can influence for example the rupture propagation direction and length (magnitude) of earthquakes along the SAF and SJF. These results should be incorporated in future seismic hazard analysis to improve predictions of ground motion from large earthquakes.
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