Imaging slip evolution on the San Andreas fault due to the 2004 Parkfield earthquake
Abstract
How dynamic earthquake ruptures transition into transient, slow deformation processes holds critical information about the condition and rheology of crustal faults. However, the detailed seismic-aseismic transition across multiple time scales remains challenging for geophysical monitoring and inference. Here we study the faulting processes associated with the 2004 Mw 6 Parkfield earthquake in California, using high-rate GPS data and strong motion records. The 1 Hz GPS data collected from 12 near-fault stations continuously document the co- and postseismic phases of the event, while tens of strong motion accelerograms capture detailed ground shaking during the event with denser spatial coverage. Using these datasets, we develop time-dependent inversion schemes to estimate slip on the fault during the earthquake and afterwards. For the coseismic period, displacement waveforms from even the nearest stations ( 1-km distance) exhibit notable discrepancy, suggesting source complexity captured by the near-field station network and hence a more stringent criterion of retrieving broadband seismogeodetic signals. We hence use seismic and geodetic data in a joint analysis to derive coseismic kinematic slip models, which are in good general agreements with previous studies. We estimate that coseismic ground shaking for stations within an epicentral distance of 30 km largely ceased within 1 min since the event initiation time, based on GPS observations and model prediction, and postseismic signals of horizontal displacements of 10 mm can be observed at some stations within hours after the event. For the postseismic period, we apply functional fits and adaptive filtering to the high-rate GPS and invert them for fault slip over time periods on the order of minutes, hours, days, and months to years after the event - the longer-term slip is based on daily GPS displacements until 2018. In particular, we assess the uncertainty of inferred fault slip for the immediate postseismic phase given noises in GPS data and modeling, as well as the general detectability of such transient fault slip. We also infer the extent of overlap between seismic and aseismic slip during and after the event, and discuss implications for the source processes and conditions of the involved fault segments of the San Andreas fault.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.G21A..05B
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 1211 Non-tectonic deformation;
- GEODESY AND GRAVITYDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS