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Radiated energy and the rupture process of the Denali Fault earthquake sequence of 2002 from broadband teleseismic body waves

George L. Choy and John Boatwright
Radiated energy and the rupture process of the Denali Fault earthquake sequence of 2002 from broadband teleseismic body waves (in The 2002 Denali Fault earthquake sequence, Charlotte Rowe (editor), Douglas Christensen (editor) and Gary Carver (editor))
Bulletin of the Seismological Society of America (December 2004) 94 (6, Part B): 269-277

Abstract

Displacement, velocity, and velocity-squared records of P and SH body waves recorded at teleseismic distances are analyzed to determine the rupture characteristics of the Denali fault, Alaska, earthquake of 3 November 2002 (M (sub w) 7.9, M (sub e) 8.1). Three episodes of rupture can be identified from broadband ( approximately 0.1-5.0 Hz) waveforms. The Denali fault earthquake started as a M (sub w) 7.3 thrust event. Subsequent right-lateral strike-slip rupture events with centroid depths of 9 km occurred about 22 and 49 sec later. The teleseismic P waves are dominated by energy at intermediate frequencies (0.1-1 Hz) radiated by the thrust event, while the SH waves are dominated by energy at lower frequencies (0.05-0.2 Hz) radiated by the strike-slip events. The strike-slip events exhibit strong directivity in the teleseismic SH waves. Correcting the recorded P-wave acceleration spectra for the effect of the free surface yields an estimate of 2.8X10 (super 15) N m for the energy radiated by the thrust event. Correcting the recorded SH-wave acceleration spectra similarly yields an estimate of 3.3X10 (super 16) N m for the energy radiated by the two strike-slip events. The average rupture velocity for the strike-slip rupture process is 1.1beta -1.2beta . The strike-slip events were located 90 and 188 km east of the epicenter. The rupture length over which significant or resolvable energy is radiated is, thus, far shorter than the 340-km fault length over which surface displacements were observed. However, the seismic moment released by these three events, 4X10 (super 20) N m, was approximately half the seismic moment determined from very low-frequency analyses of the earthquake. The difference in seismic moment can be reasonably attributed to slip on fault segments that did not radiate significant or coherent seismic energy. These results suggest that very large and great strike-slip earthquakes can generate stress pulses that rapidly produce substantial slip with negligible stress drop and little discernible radiated energy on fault segments distant from the initial point of nucleation. The existence of this energy-deficient rupture mode has important implications for the evaluation of the seismic hazard of very large strike-slip earthquakes.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 94
Serial Issue: 6, Part B
Title: Radiated energy and the rupture process of the Denali Fault earthquake sequence of 2002 from broadband teleseismic body waves
Title: The 2002 Denali Fault earthquake sequence
Author(s): Choy, George L.Boatwright, John
Author(s): Rowe, Charlotteeditor
Author(s): Christensen, Douglaseditor
Author(s): Carver, Garyeditor
Affiliation: U. S. Geological Survey, Denver, CO, United States
Affiliation: Los Alamos National Laboratory, Los Alamos, NM, United States
Pages: 269-277
Published: 200412
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 18
Accession Number: 2005-040995
Categories: SeismologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
N62°00'00" - N64°00'00", W148°00'00" - W142°00'00"
Secondary Affiliation: University of Alaska, USA, United StatesCarver Geologic, Kodiak, AK, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200525
Program Name: USGSOPNon-USGS publications with USGS authors
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