Last updated 29 March 2011
A magnitude 6.3 earthquake occurred Tuesday, February 22, 2011, at 12:51:43 PM local time (Feb. 21, 2011 at 23:51:43 UTC), close to Christchurch, New Zealand. No tsunami was reported. At least 160 people died with many more left missing.
GNS scientists in New Zealand have been measuring and analyzing data from this quake (Fig. 1) and results are plotted on the GeoNet web page. Members of this community explain some of their findings in videos at the GNS Science web page.
At UNAVCO, movement at local GPS stations in N.Z. has been determined using distances between sites. See Figures 2 and 3 for the time-series plots from two GPS stations near Christchurch and the resulting coseismic offsets. Their locations are mapped in Figure 4.
Various U.S. organizations are involved in reconnaissance and measuring in the field, following this earthquake. For example, the Geo-engineering Extreme Event Reconnaissance (GEER) team will be working with colleagues in New Zealand to provide shear-wave velocity profiling at strong-motion stations and liquefaction sites.
Located at the easternmost limit of previous aftershocks from the September 4th, 2010, event, this earthquake is broadly associated with regional plate boundary deformation where the Pacific and Australia plates interact in the central South Island, New Zealand.
According to GeoNet, preliminary analysis of seismograph records of the devastating magnitude 6.3 earthquake on Tuesday indicates that it was 9 km from the centre of Christchurch on a buried fault oriented roughly east-west.
"There is no obvious structure directly connecting the faults that ruptured in the September’s magnitude 7.1 earthquake with the fault that generated the magnitude 6.3 event. On the contrary, precise aftershock relocations suggest that at least two north-east/south-west trending faults lie between the two and that there is no evidence from the earthquake data of an extension of the Greendale Fault."
"The M 6.3 mainshock and a couple other events in the aftershock sequence are reverse (thrust) faulting mechanisms. Also the two events furthest to the west are mainly reverse faulting and may be considered as part of the aftershock sequence to the September M 7.1 earthquake rather than the February 22 earthquake. Most of the remaining mechanisms are strike-slip or mainly strike-slip solutions although the orientation of the fault plane is variable."
Relevant Links and Science
Figure 1 - Map showing the mainshock and aftershocks above magnitude 3, and fault ruptures in Canterbury. Aftershock locations and buried fault locations (dashed yellow lines) are preliminary Provided by GeoNet. [Click to enlarge]
Figure 2 - This SAR interferogram was made by combining a sequence of radar images acquired by an orbiting satellite before and after a quake. It shows precise measurements of ground displacement that occurred between the time of the image acquisitions. The colored bands or fringes represent movement towards or away from the spacecraft. Peak ground motion is measured to be almost 50 cm towards the satellite, and shows that the focus of the tremor was under the city's southeastern suburbs. Image from COMET, modified by the BBC. [Click to enlarge]
Figure 3 - Time series of GPS positions at Lyttleton (LYTT) before and after the earthquake of February 22, 2011. Three vertical black lines indicate the timing of the initial M6.3 event, and aftershocks of M5.7 and 5.5 that immediately followed. Total coseismic offsets at LYTT (located ~3.4 km to the southeast (148 degrees) from the epicenter location indicated on the USGS web page) are estimated to be 22 cm South, 14 cm West, and 7 cm Up. Epoch-by-epoch analysis was done using TRACK software with respect to station METH, 93 km to the WNW. Data from LYTT are not yet available for Feb. 22. (H. Berglund, UNAVCO) [Click to enlarge]
Figure 4 - Time series of GPS positions at station MQZG over a 48 hour period starting on February 21st, 2011. Three vertical black lines indicate the timing of the initial M6.3 event, and aftershocks of M5.7 and 5.5 that immediately followed. MQZG, which lies farther from the epicenter than LYTT, moved approximately 5 cm South and 3 cm West during this 48-hour period. Epoch-by-epoch analysis was done using TRACK software with respect to station METH, 90 km to the WNW. (H. Berglund, UNAVCO. [Click to enlarge]
Figure 5 - Map of USGS epicentral location and focal mechanism showing GPS stations LYTT, MQZG and METH. (H. Berglund, UNAVCO) [Click to enlarge]
Figure 6 - Rescuers serach for trapped survivors in a collapsed building in the Feb. 21st M6.3 earthquake in New Zealand. Photo by Mark Mitchell, AP Photo/New Zealand Herald.
Last modified Thursday, 31-Mar-2011 18:10:28 UTC