RAPID: Recording Fault-Zone Trapped Waves from Aftershocks of the M6.3 Christchurch Earthquake Sequence in New Zealand to Document the Subsurface Damage Zones

点击翻译按钮获取中文摘要

The M6.3 Christchurch earthquake struck the Canterbury region in New Zealand's South Island on 22February 2011, causing widespread damage and multiple fatalities. The earthquake occurred at 5 kmdepth, 10 km south-east of Christchurch, New Zealand's 2nd-most populous city. It followed ~6 monthsafter the Sept. 4, 2010 M7.1 Darfield earthquake in the same region. The Christchurch earthquake waspart of a series of earthquakes and aftershocks in the region following the 2010 M7.1 Darfield. NewZealand's GNS Science describe it as "technically an aftershock" of the earlier event while otherseismologists from USA and Australia consider it a separate event, given its location on a separate faultsystem. Seismologically, this M6.3 quake is classed as an aftershock because of its relationship to theongoing activity since September last year. However, it has generated a significant series of its ownaftershocks, many of which are considered big for a M6.3 earthquake. Over 200 aftershocks including aM5.7 were experienced in the first week. It did not occur on the Greendale Fault, on which the 2010 M7.1Darfield quake occurred, but on a previously unknown blind fault line running 17 km east-west south ofChristchurch, at depths of 3?12 km. On the contrary, precise aftershock relocations suggest that at leasttwo north-east/south-west trending faults lie between the two and that there is no evidence from theearthquake data of an extension of the Greendale Fault. However, there are still many aftershocks of the2010 M7.1 Darfield earthquake spread along the fault line of the 2011 M6.3 Christchurch earthquake.In order to document the complicated subsurface structure of the damage zones caused by thesequence of the 2010 M7.1 Darfield and the 2011 M6.3 Christchurch earthquakes in the Canterburyregion of NZ?s South Island, the investigator proposes to record fault-zone trapped waves (FZTWs) generated byaftershocks, and use the FZTWs to image the rupture zones composed by damaged fault rocks atseismogenic depths. Because the amplitude and dispersive feature of FZTWs are sensitive to thegeometry and physical properties, and the location of aftershocks (within or outside) of the low-velocityfault-zone waveguide formed by severely damaged rocks in these two earthquakes, observations andnumerical modeling of recorded FZTWs allow us to learn more about (1) the width, velocity reduction, Qvalue and depth extension of damage zones of the 2010 M7.2 and 2011 M6.3 earthquakes, (2) the shapeof subsurface rupture zones with the principal slip plans of the mainshocks, and if the two rupturesegments are connected at seismogenic depths, (3) the difference in rock damage magnitude caused bythese two earthquakes occurring at different depths with different sizes, (4) the fault healing with timeafter the mainshock.This RAMP experiment will be collaborated by USC/UoA /UoC/GNS in NZ to pursue the value ofthe work proposed, likewise with the ongoing efforts by the NZ national GEONET seismic network andresearchers. GNS will offer to follow the USC/UoA/UoC work and help them keep up with otherinitiatives and projects concerning the Darfield event.