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Slow-Growing and Extended-Duration Seismicity Swarms: Reactivating Joints or Foliations in the Cahuilla Valley Pluton, Central Peninsular Ranges, Southern California

Hauksson, Egill and Ross, Zachary E. and Cochran, Elizabeth (2019) Slow-Growing and Extended-Duration Seismicity Swarms: Reactivating Joints or Foliations in the Cahuilla Valley Pluton, Central Peninsular Ranges, Southern California. Journal of Geophysical Research. Solid Earth, 124 (4). pp. 3933-3949. ISSN 2169-9313. doi:10.1029/2019jb017494.

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Three prolific earthquake swarms and numerous smaller ones have occurred since 1980 in the Mesozoic igneous plutonic rocks of the Perris block of the Peninsular Ranges, Southern California. The major swarms occurred in 1980–1981, 1983–1984, and 2016–2018, with the latest swarm still ongoing. These swarms have no clear mainshock, with the largest events of M_L 3.6, M_L 3.7, and M_w 4.4. Each successive swarm had larger cumulative seismic moment release with about 314 and 411 events of M ≥ 1.5, while the third swarm has produced about 451 events of M ≥ 1.5 (as of September 2018). The concurrent strike‐slip faulting occurred on north to northwest striking planes but with no orthogonal northeast trending seismicity alignments. These shallow swarms are probably driven by intrablock Pacific‐North America plate boundary stress loading of the two bounding major late Quaternary strike‐slip faults, the Elsinore and San Jacinto faults. The state of stress within the Cahuilla Valley pluton has a ~40° angle between the maximum principal stress and the average trend of the swarms, suggesting that migrating pore fluid pressures aid in the formation and growth of zones of weakness. These swarms, which last more than 600 days each, exhibit clear bilateral spatial migration for distances of up to ~7–8 km and reach their full length in about 20 months. The slow spatial‐temporal development of the swarms corresponds to a fluid diffusivity of 0.006 to 0.01 m2/s, consistent with very low permeability rocks as expected for this block. There is no geodetic or other evidence for a slow slip event driving the swarms.

Item Type:Article
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URLURL TypeDescription
Hauksson, Egill0000-0002-6834-5051
Ross, Zachary E.0000-0002-6343-8400
Cochran, Elizabeth0000-0003-2485-4484
Additional Information:© 2019 American Geophysical Union. Received 2 FEB 2019; Accepted 24 MAR 2019; Accepted article online 28 MAR 2019; Published online 15 APR 2019. We thank L. M. Jones, M‐A Meier, and J. Stock for discussions and R. Graves, K. Scharer, and D. Kilb for comprehensive reviews. This research was supported by USGS/NEHRP grants G16AP00147 and G18AP00028; by NSF awards EAR‐1550704 and EAR‐1818582; and by the Southern California Earthquake Center (contribution no. 9027). SCEC is funded by NSF Cooperative Agreement EAR‐1600087 and USGS Cooperative Agreement G17AC00047. We used GMT from Wessel et al. (2013) to make the figures. We have used waveforms and parametric data from the Caltech/USGS Southern California Seismic Network (SCSN), doi: 10.7914/SN/CI, stored at the Southern California Earthquake Data Center. doi:10.7909/C3WD3xH1. There are no real or perceived financial conflicts of interests for any author.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:seismicity migration; Earthquake swarms; hydraulic diffusivity; southern California; state of stress; Cahuilla pluton
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Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center9027
Issue or Number:4
Record Number:CaltechAUTHORS:20190328-103308099
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Official Citation:Hauksson, E., Ross, Z. E., & Cochran, E. (2019). Slow‐growing and extended‐duration seismicity swarms: Reactivating joints or foliations in the Cahuilla Valley pluton, central Peninsular Ranges, Southern California. Journal of Geophysical Research: Solid Earth, 124, 3933–3949.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94244
Deposited By: George Porter
Deposited On:28 Mar 2019 18:12
Last Modified:16 Nov 2021 17:03

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