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Were the 1952 Kern County and 1933 Long Beach, California, Earthquakes Induced?

Susan E. Hough, Victor C. Tsai, Robert L. Walker, Morgan T. Page, & Seyed M. Hosseini

Published July 29, 2016, SCEC Contribution #6401, 2016 SCEC Annual Meeting Poster #171

Several recent studies have presented evidence that significant induced earthquakes occurred in a number of regions during the 20th century related to either production or early wastewater injection. We consider whether the Mw6.4 Long Beach and Mw7.3 1952 Kern County earthquakes might have been induced by production in the Huntington Beach and Wheeler Ridge oil fields, respectively. The Long Beach earthquake occurred within 9 months of the start of directional drilling that first exploited offshore tideland reserves at depths of ≈1200 m; the well location was within ≈3 km of the event epicenter. The Kern County earthquake occurred 111 days following the first exploitation of deep Eocene production horizons within the Wheeler Ridge field at depths reaching 3 km, within ≈1 km of the White Wolf fault (WWF); the epicenter of this earthquake is poorly constrained but the preferred epicenter is within ≈7 km of the well. While production in the Wheeler Ridge field would have likely reduced pore pressure, inhibiting failure on the WWF assuming a Coulomb failure criteria, we present a model based on analytical solutions with model parameters constrained from detailed industry data, whereby direct pore pressure effects were blocked by a normal fault that created an impermeable barrier close to the WWF, allowing the normal stress change associated with production to dominate, thereby promoting failure by unclamping the fault. Our proposed triggering mechanism is consistent with the observation that significant earthquakes are only rarely induced by production in proximity to major faults. Our results also suggest that significant induced earthquakes in southern California during the early 20th century might have been associated with industry practices that are no longer employed (i.e., production without water re-injection). The occurrence of significant earthquakes during the earthquake 20th century therefore does not necessarily imply a high likely of induced earthquakes at the present time.

Key Words
Induced earthquakes

Hough, S. E., Tsai, V. C., Walker, R. L., Page, M. T., & Hosseini, S. M. (2016, 07). Were the 1952 Kern County and 1933 Long Beach, California, Earthquakes Induced?. Poster Presentation at 2016 SCEC Annual Meeting.

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