Detection Limits and Near-Field Ground Motions of Fast and Slow Earthquakes

Session: Earthquake Source Parameters: Theory, Observations and Interpretations
Type: Oral
Date: 4/30/2020
Time: 02:00 PM
Room: 120 + 130
Description: 

We investigate theoretical limits to detect fast and slow seismic events and spatial variations of ground motion expected from M6 earthquakes at short epicentral distances. The analysis is based on synthetic velocity seismograms calculated with the discrete wavenumber method assuming seismic velocities and attenuation properties of the crust in Southern California. The examined source properties include different magnitudes (M -1.0 to M 6.0), static stress drops (0.1-10 MPa), slow and fast ruptures (0.1-0.9 of shear wave velocity). For the M6 events we also consider variations in rise times producing crack- and pulse-type events and different rupture directivities. Slow crack-type events produce ground motion with considerably lower amplitude than corresponding regular fast earthquakes with the same magnitude, and hence are significantly more difficult to detect. The static stress drop and slip rise time also affect the maximum radiated seismic motion, and hence event detectability. For larger earthquakes at short epicentral distances effects associated with rupture propagation become more important. Rupture directivity affects the shape of ground motion curves, while rupture velocity and rise time influence only the ground motion amplitudes. The surface ground motion distribution of slowly propagating or crack-type events is dominated by the focal mechanism and involves low level of motion. The ground motion distribution of fast earthquakes is affected significantly by rupture directivity and has large motions in the direction(s) of rupture propagation. The rise time and, hence, rupture type (crack vs. pulse type) has a profound effect on the level of ground motions. The results can help optimizing detection of slow and fast earthquakes and understand the spatial distribution of ground motion generated by large events with important implications for near-fault seismic hazard assessment.

Presenting Author: Grzegorz Kwiatek

Authors