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Relating Magnitude to Fault Slip Characteristics from Geodetic Data


Researchers: Clayton M. J. Brengman, William D. Barnhart, Emma H. Mankin, and Cody N. Miller, University of Iowa.

Written by Linda Rowan
31 July 2019


Summary

The magnitude of an earthquake is correlated with the area of fault that slipped and typically an empirical relation is derived through finite fault models and aftershock data. Utilizing 111 geodetic slip distributions for 73 earthquakes with magnitudes from 5.3 to 9.1, fault characteristics are correlated with magnitude. Key insights are that the area of fault slip is smaller for a given magnitude than those for seismic models. Geodetic data provides a different method to build or enhance empirical relations between magnitude and slip characteristics to improve our understanding of earthquake processes and enhance rapid assessment of earthquake risks and responses.


Observations

Earthquakes defined by seismic data, primarily finite fault models and aftershock distribution, show empirical relationships between the magnitude and size (i.e., the amount of slip and the area of the rupture). Another way to consider such relationships is with observations from a growing fleet of geodetic tools, such as Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR). Geodetic observations can be utilized to define empirical relationships between magnitude and slip. Here, GNSS and InSAR observations for 73 earthquakes around the world with magnitudes from 5.3 to 9.1 were organized into common parameters, had biases removed and then solved for the best fitting slip distribution. The slip distributions were then regressed with their magnitudes to determine the empirical relations.


Results

The geodetically derived slip distributions showed distinctive shapes related to magnitude that might be exploited in the future to understand earthquake evolution. When the slip distributions were related to magnitudes, the result show the amount of slip is smaller for earthquakes of magnitude less than 7.2 and larger for events larger than 7.2 compared with the empirical relations derived from the seismic data. The seismic relations overpredict the fault area affected by an earthquake of small to moderate magnitude. The affect is likely even more pronounced given that the geodetic slip distributions contain some afterslip. The empirical relations derived from geodetic data provide a different approach to understanding earthquakes and informing hazard assessment and response to an event.

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Reference

Clayton M. J. Brengman, William D. Barnhart, Emma H. Mankin, Cody N. Miller; Earthquake‐Scaling Relationships from Geodetically Derived Slip Distributions. Bulletin of the Seismological Society of America doi: 10.1785/0120190048.

Keywords

magnitude, slip area, slip length, slip width, InSAR, GNSS


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Last modified: 2020-01-28  22:16:23  America/Denver