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Fault location and slip distribution of the 22 February 2011 M (sub w) 6.2 Christchurch, New Zealand, earthquake from geodetic data

John Beavan, Eric Fielding, Mahdi Motagh, Sergey Samsonov and Nic Donnelly
Fault location and slip distribution of the 22 February 2011 M (sub w) 6.2 Christchurch, New Zealand, earthquake from geodetic data
Seismological Research Letters (November 2011) 82 (6): 789-799

Abstract

The 22 February (local time) MW nearly equal 6.2 Christchurch earthquake occurred within the aftershock region of the 4 September 2010 MW 7.1 Darfield (Canterbury) earthquake). Both the Darfield and Christchurch earthquakes occurred on previously unknown faults in a region of historically low seismicity, but within the zone of plate boundary deformation between the Pacific and Australian plates. The Darfield earthquake caused surface rupture up to 5 m, but none has been observed associated with the Christchurch earthquake. Geodetic data indicate that strain has been slowly accumulating within the region, and the presence of active subsurface faults was known or suspected. Earthquakes of magnitude up to 7.2 in this region had been allowed for in the national seismic hazard model, but the observed high apparent stresses and high ground accelerations had not been anticipated, particularly those experienced in the Christchurch event. These and other factors, plus the close proximity of the February earthquake to Christchurch city center, were responsible for the major damage caused by the earthquake. A large amount of geodetic ground-displacement data is available to constrain the source of the earthquake, in part because we reoccupied nearly 200 GPS sites that had been observed following the Darfield earthquake, and in part because a number of space agencies collected synthetic aperture radar (SAR) data over the source area that we were able to use in differential interferometric SAR (DInSAR) processing. The geodetic data were collected one day to seven weeks following the February earthquake, so they include ground deformation due to aftershocks, in particular the MW 5.8 and MW 5.9 events that occurred within two hours of the mainshock. To first order, the earthquake source can be modeled as a planar fault striking nearly equal 59 degrees and dipping nearly equal 69 degrees to the southeast. The peak slip of 2.5-3 m is a mixture of reverse and right-lateral slip and is located nearly equal 7 km east-southeast of Christchurch city center at a depth of nearly equal 4 km. Slip of nearly equal 1 m reaches within nearly equal 1 km of the ground surface. The slip near the southwest end of the plane is approximately right-lateral with magnitude nearly equal 1 m. The geodetic data are significantly better fit by two fault planes, a compact region of oblique slip on the fault described above, plus right-lateral strike slip on a near-vertical fault to its southwest that coincides with the locations of the two major aftershocks and with a trend of smaller aftershocks. A lobe of ground uplift seen in some of the SAR data (e.g., Figure 4) just west of the main slip patch is not well modeled, and suggests some slip may also have occurred elsewhere, perhaps on a splay off the main fault plane.


ISSN: 0895-0695
EISSN: 1938-2057
Coden: EAQNAT
Serial Title: Seismological Research Letters
Serial Volume: 82
Serial Issue: 6
Title: Fault location and slip distribution of the 22 February 2011 M (sub w) 6.2 Christchurch, New Zealand, earthquake from geodetic data
Affiliation: GNS Science, Lower Hutt, New Zealand
Pages: 789-799
Published: 20111112
Text Language: English
Publisher: Seismological Society of America, El Cerrito, CA, United States
References: 30
Accession Number: 2012-014170
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
S43°32'60" - S43°32'60", E172°40'00" - E172°40'00"
Secondary Affiliation: Jet Propulsion Laboratory, USA, United StatesHelmholtz Centre Potsdam, DEU, GermanyEuropean Center for Geodynamics and Seismology, CAN, CanadaLand Information New Zealand, NZL, New Zealand
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201208
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