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What can surface-slip distributions tell us about fault connectivity at depth?

David D. Oglesby
What can surface-slip distributions tell us about fault connectivity at depth?
Bulletin of the Seismological Society of America (April 2020) 110 (3): 1025-1036


Fault systems with stepovers and gaps along strike are ubiquitous in nature, and many modern earthquakes (e.g., 1992 Landers, 1999 Hector Mine, 2016 Kaikoura, and 2019 Ridgecrest) have shown that ruptures can readily propagate across some disconnections, while being halted by others. It is quite possible, however, that many faults that appear discontinuous at the surface are in fact connected at depth, facilitating throughgoing rupture, and potentially increasing earthquake size. The present work explores whether the mapped surface slip in an earthquake is indicative of the connectivity of the fault system at depth. If there is a signal of subsurface connectivity in the surface-slip pattern, then the connectivity of the system could potentially be inferred. Through 3D dynamic rupture modeling of faults with along-strike gaps of various depths, I explore whether the amplitude or the spatial distribution of slip after an earthquake could be used to diagnose fault connectivity at depth. I find that, in general, fault segments that are connected up to shallow depths of 1-2 km and are relatively long along strike compared to the seismogenic depth tend to have higher slip gradients at their edges than faults that are connected at greater depth, or that are disconnected to the bottom of the seismogenic zone. Systematic slip gradient differences at fault segment edges have been recorded in past earthquakes, giving hope that the modeled effect can be detected in many cases, even though mapped surface slip is affected by a number of different sources of heterogeneity. The results provide an alternative explanation for observations that stepovers that allow throughgoing rupture tend to have higher slip gradients than those at which rupture terminates: perhaps many such stepovers are connected at depth, which could persistently favor throughgoing rupture. There may be implications for interpretation of apparent fault discontinuities worldwide.

ISSN: 0037-1106
EISSN: 1943-3573
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 110
Serial Issue: 3
Title: What can surface-slip distributions tell us about fault connectivity at depth?
Author(s): Oglesby, David D.
Affiliation: University of California Riverside, Department of Earth and Planetary Sciences, Riverside, CA, United States
Pages: 1025-1036
Published: 20200407
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 35
Accession Number: 2020-039347
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202025
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