Earthquake stress drop is an important source parameter that directly links to strong ground motion and fundamental questions in earthquake physics. Stress drop estimations may contain significant uncertainties due to such factors as variations in material properties and data limitations, which limit the applications of stress drop interpretations. Using a high‐resolution borehole network, we estimate stress drop for 4551 (M0‐4) earthquakes on the San Andreas Fault at Parkfield, California, between 2001 and 2016 using spectral decomposition and an improved stacking method. To evaluate the influence of spatiotemporal variations of material properties on stress drop estimations, we apply different strategies to account for spatial variations of velocity and attenuation changes, and divide earthquakes into three separate time periods to correct temporal variations of attenuation. These results show that appropriate corrections can significantly reduce the scatter in stress drop estimates, and decrease apparent depth and magnitude dependence. We find that insufficient bandwidth can cause systematic underestimation of stress drop estimates and increased scatter. The stress drop measurements from the high‐frequency borehole recordings exhibit complex stable spatial patterns with no clear correlation with the nature of fault slip, or the slip distribution of the 2004 M6 earthquake. Temporal variations are significantly smaller, less well resolved and varying spatially. They do not affect the long‐term stress drop spatial variations, suggesting local material properties may control the spatial heterogeneity of stress drop.
We combine earthquake spectra from multiple studies to investigate whether the increase in stress drop with depth often observed in the crust is real, or an artifact of decreasing attenuation (increasing
- NSF-PAR ID:
- 10372147
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 126
- Issue:
- 10
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We calculate rupture directivity and velocity for earthquakes in three well‐recorded repeating sequences (2001–2016) on the San Andreas Fault at Parkfield using
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