EARTHQUAKE SUMMARY MAPU.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

2009

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N E W H E B RIDES TRE NC H

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P A C I F I CP L A T E

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M6.3 South Island, New Zealand Earthquake of 21 February 2011

0 200 400100Kilometers

Mercator Projection

A U S T R A L I ANew Caledonia

VANUATU

NEW ZEALAND

Brisbane

Sydney

AucklandMelbourne

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0 400 800 1,200 1,600200Kilometers

Prepared in cooperation with the Global Seismographic Network

Tectonic Setting

Seismic Hazard

Epicentral Region

M6.3 South Island, New Zealand Earthquake of 21 February 2011 21 February 2011 23:51:43 UTC 43.6° S., 172.71° E.Depth 5 kmMw = 6.3 (USGS)

Tectonic Summary

The February 21, 2011 South Island, New Zealand earthquake occurred as part ofthe aftershock sequence of the M 7.1 September 3, 2010 Darfield, NZearthquake. The February 21 earthquake involved oblique-thrust faulting at theeasternmost limit of previous aftershocks, and like the mainshock itself is broadlyassociated with regional plate boundary deformation as the Pacific and Australiaplates interact in the central South Island, New Zealand.

This latest shock is significantly closer to the main population center ofChristchurch, NZ, than is the September 2010 mainshock, in the vicinity ofseveral other moderate (M 4 - 5) sized aftershocks located east of the mainrupture zone of the 2010 event. There is no specific structure directly linking thisevent to the main fault of the 2010 mainshock, although there have beennumerous aftershocks along generally east-west linear trends extending east fromthe end of the previous rupture. The north or north-east trends to the possiblefault planes and the oblique thrust faulting mechanism as seen in the focalmechanism solution may reflect an association with similarly- trending faultspreviously mapped in the Port Hills region, just to the south of Christchurch.

Since the September 3, 2010 mainshock, there have been approximately 6M>=5.0 aftershocks in the Christchurch region. The February 21 earthquakerepresents the largest aftershock to date, more that half a magnitude unit largerthan the previous largest aftershock.

EXPLANATIONEarthquake Magnitude

5.50 - 5.996.00 - 6.997.00 - 7.99≥ 8.00

Earthquake Depth0 - 6970 - 299≥ 300

Seismic hazard is expressed as peakground acceleration (PGA) on firmrock, in meters/sec², expected to beexceeded in a 50-yr period with aprobability of 10 percent.

EXPLANATIONMag ≥ 7.0

0 - 69 km70 - 299300 - 600

Plate BoundarySubductionTransformDivergentOthers

Volcanoes

RELATIVE PLATE MOTIONS

The broad red vectors represent the motion of tectonic platesrelative to the adjacent plate. In the vicinity of this earthquake,the Australia Plate and Pacific Plate are converging at about 35-45 mm/yr along the Puysegur Trench.

0 400 800 1,200 1,600200Kilometers

Significant Earthquakes Mag >= 7.5

Year Mon Day Time Lat Long Dep Mag1929 06 16 2247 -41.831 172.292 35 7.51931 02 02 2246 -39.772 176.025 35 7.71943 09 06 0341 -53.000 159.000 0 7.61981 05 25 0525 -48.721 164.658 8.6 7.61989 05 23 1054 -52.507 160.602 4.3 8.12004 12 23 1459 -49.312 161.345 10 8.12007 10 15 1229 -44.80 167.55 18 6.82010 09 03 1635 -43.52 171.83 12 7.0

Peak Ground Acceleration in m/sec**2

.2 .4 .8 1.6 2.4 3.2 4.0 4.8

Epicentral Region

Epicentral Region

DATA SOURCES and REFERENCES

EARTHQUAKES AND SEISMIC HAZARD USGS, National Earthquake Information Center NOAA, National Geophysical Data Center IASPEI, Centennial Catalog (1900 - 1999) and extensions Engdahl, E.R. and Villaseñor, A., 2002, Global Seismicity: 1900 - 1999, chap. 41 of Lee, W.H.K., and others,eds., International Earthquake and Engineering Seismology, Part A: New York, N.Y., Elsevier Academeic Press, 932 p.HDF (unpublished earthquake catalog) (Engdahl, 2003)Global Seismic Hazard Assessment Program http://www.seismo.ethz.ch/GSHAP/

DISCLAIMER

Base map data, such as place names and political boundaries, are the best available but may not be current or may contain inaccuracies and therefore should not be regraded as having official signifiance.

Map prepared by U.S. Geological Survey National Earthquake Information Center21 February 2011http://earthquake.usgs.gov/Map not approved for release by Director USGS

PLATE TECTONICSBird, P., 2003, An updated digital model of plate boundaries: Geochem. Geophys. Geosyst., v. 4, no. 3, pp. 1027- 80.

BASE MAP NIMA and ESRI, Digital Chart of the World USGS, EROS Data Center NOAA GEBCO and GLOBE Elevation Models

PAGER

ShakeMap