The Enola, Arkansas, Intraplate Swarm of 2001

Ivan Rabak; Charles Langston; Paul Bodin; Steve Horton; Mitch Withers; Christine Powell

doi:10.1785/gssrl.81.3.549

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Other| May 01, 2010

The Enola, Arkansas, Intraplate Swarm of 2001

Ivan Rabak;

Ivan Rabak

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

2

Now at Geodesy Laboratory and PANGA Data Analysis Facility, Department of Geological Sciences, Central Washington, University, Ellensburg, Washington, USA

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Charles Langston;

Charles Langston

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

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Paul Bodin;

Paul Bodin

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

3

University of Washington, Department of Earth and Space Sciences, Seattle, Washington

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Steve Horton;

Steve Horton

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

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Mitch Withers;

Mitch Withers

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

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Christine Powell

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

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Author and Article Information

Ivan Rabak

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

2

Now at Geodesy Laboratory and PANGA Data Analysis Facility, Department of Geological Sciences, Central Washington, University, Ellensburg, Washington, USA

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Charles Langston

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Paul Bodin

3

University of Washington, Department of Earth and Space Sciences, Seattle, Washington

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Steve Horton

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Mitch Withers

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Christine Powell

1

Center for Earthquake Research and Information (CERI), University of Memphis, Memphis, Tennessee

University of Washington  Department of Earth and Space Sciences  Box 351310  Seattle, Washington 98195-1310 U.S.A.  [email protected]  (P. B.)

Publisher: Seismological Society of America

First Online: 09 Mar 2017

Online ISSN: 1938-2057

Print ISSN: 0895-0695

Seismological Research Letters (2010) 81 (3): 549–559.

https://doi.org/10.1785/gssrl.81.3.549

Abstract

The 2001 Enola earthquake sequence started with an M 4.4 mainshock and was followed by 2,500 earthquakes in two months, confined in a crustal volume of 8 km³, at depths between 4 and 6 km. We have computed precise absolute and relative hypocentral locations using relative travel times based on waveform cross-correlation and a double-difference relative hypocentral location method. Focal mechanisms were computed using P-, SV-, and SH-wave polarities. Highly similar strike-slip focal mechanisms are consistent with the stress regime of the mid-continent province. The swarm volume produced two clusters of earthquakes at different depths and times. We speculate that these clusters represent a system of conduits possibly filled by fluids. The focal mechanisms of the first, seismically deeper sequence show a strong thrust component, while the later and shallower cluster solutions show predominant strike-slip motion. Daily seismicity rates reveal short and sudden increases in activity rather than typical aftershock decay. A b-value of 0.9 is observed for the entire swarm. The sequence appears to recapitulate aspects of a more intense earthquake swarm in the same area in 1981.