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Published October 7, 2016 | Supplemental Material
Journal Article Open

Localized seismic deformation in the upper mantle revealed by dense seismic arrays


Seismicity along continental transform faults is usually confined to the upper half of the crust, but the Newport-Inglewood fault (NIF), a major fault traversing the Los Angeles basin, is seismically active down to the upper mantle. We use seismic array analysis to illuminate the seismogenic root of the NIF beneath Long Beach, California, and identify seismicity in an actively deforming localized zone penetrating the lithospheric mantle. Deep earthquakes, which are spatially correlated with geochemical evidence of a fluid pathway from the mantle, as well as with a sharp vertical offset in the lithosphere-asthenosphere boundary, exhibit narrow size distribution and weak temporal clustering. We attribute these characteristics to a transition from strong to weak interaction regimes in a system of seismic asperities embedded in a ductile fault zone matrix.

Additional Information

© 2016 American Association for the Advancement of Science. 23 December 2015; accepted 31 August 2016. We thank Signal Hill Petroleum and NodalSeismic for granting us permission to use the Long Beach Array data, and we thank Breitburn Energy and LA Seismic for permission to use the Rosecrans Array data. We acknowledge J. P. Avouac, R. Bürgmann, Y. Ma, and W. Frank for helpful discussions. This research was supported by NSF awards EAR-1214912 and EAR-1520081 and by the Terrestrial Hazard Observation and Reporting Center at Caltech. The seismic data are property of Signal Hill Petroleum and Breitburn Energy. Data are available for noncommercial use through a license agreement with the data owners that includes but is not limited to a nondistribution agreement. Please contact the authors for additional information.

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