Abstract
AbstractWe investigate theoretical limits to detection of fast and slow seismic events, and spatial variations of ground motion expected from M 6 earthquakes at short epicentral distances. The analyses are 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), and slow and fast ruptures (0.1–0.9 of shear wave velocity). For the M 6 events we also consider variations in rise times producing crack‐ and pulse‐type events and different rupture directivities. Slow 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. Apart from geometrical factors, the saturation and depletion of seismic ground motion at short epicentral distances stem from radiation pattern, earthquake size (magnitude, stress drop), and rupture directivity. The rupture velocity, rise time, and directivity affect significantly the spatial pattern of the ground motions. The results can help optimizing detection of slow and fast small earthquakes and understand the spatial distribution of ground motion generated by large events.
Highlights
In the last two decades, significant progress in acquisition of seismic and geodetic data, coupled with improved analysis techniques and computing power, have led to detection of very small earthquakes, nonvolcanic tremor, and slow slip events (e.g., Dragert et al, 2004; Obara, 2002; Ross et al, 2019; Shelly et al, 2007)
Using the discrete wavenumber method to simulate seismograms of earthquakes with magnitudes ranging from −1.0 to 6.0, we investigate the influence of various seismic source characteristics on detection limits and ground motion distributions at short epicentral distances
We examine the influence of magnitude, stress drop, and rupture velocity on signal‐ to‐noise ratio (SNR) of events at distances not exceeding 50 km
Summary
In the last two decades, significant progress in acquisition of seismic and geodetic data, coupled with improved analysis techniques and computing power, have led to detection of very small earthquakes, nonvolcanic tremor, and slow slip events (e.g., Dragert et al, 2004; Obara, 2002; Ross et al, 2019; Shelly et al, 2007). Theoretical constraints on plausible properties of motion generated by different types of slip events on faults at different source‐receiver configurations can help separating tectonic from other sources of weak ground motion. This can be especially useful for automated techniques that process vast data sets and do not include validation of the nature of the detected sources
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