{"id":6292,"date":"2011-06-13T23:20:41","date_gmt":"2011-06-14T04:20:41","guid":{"rendered":"http:\/\/all-geo.org\/highlyallochthonous\/?p=6292"},"modified":"2011-06-14T14:44:48","modified_gmt":"2011-06-14T19:44:48","slug":"more-large-aftershocks-rattle-christchurch-will-it-ever-end","status":"publish","type":"post","link":"https:\/\/all-geo.org\/highlyallochthonous\/2011\/06\/more-large-aftershocks-rattle-christchurch-will-it-ever-end\/","title":{"rendered":"More large aftershocks rattle Christchurch: will it ever end?"},"content":{"rendered":"

\"A<\/span>Poor Christchurch just can’t seem to catch a seismic break this year: two more powerful aftershocks shook the city early Monday afternoon local time: the first a magnitude 5.3 (Geonet<\/a>, USGS<\/a>), the second a magnitude 6 (Geonet<\/a>, USGS<\/a>). The focal mechanisms of both shocks indicate mostly pure strike-slip motion, probably dextral strike-slip along a northeast-southwest oriented fault plane; the M6 quake also has a component of roughly east-west compression. These focal mechanisms are very similar to the magnitude 7 Darfield earthquake last September<\/a> and the magnitude 6.3<\/a> rupture that badly damaged the city in February. These latest tremors occurred a few kilometres to the east of February’s quake, and from their location and the manner in which they ruptured, it looks like these earthquakes were on another, more easterly segment of the same fault. <\/p>\n

\"\"

Focal mechanisms and locations for the two large June 13 aftershocks, compared to the September 2010 and February 2011 ruptures. White lines are rough fault traces.<\/p><\/div>\n

Fortunately, there appear have been few casualties this time around, but a new violent tremor is not good news for the many already damaged buildings in Christchurch. Peak ground accelerations from the M6 shock<\/a> were quite high in the southern parts of the city (0.7-0.8g mostly, although one instrument recorded a 2.1g acceleration). The BBC reports that several buildings have collapsed<\/a>, and there have also been further rockfalls<\/a>, perhaps from cliffs already weakened by the previous earthquakes. Once again, the shaking has also caused extensive liquefaction in Christchurch<\/a> and its suburbs<\/a>, exacerbating the damage and destruction. <\/p>\n

\"\"<\/a>

An SUV engulfed in mud caused by seismic liquefaction. Source: The Australian.<\/p><\/div>\n