Collaborative Research: Seismic and Aseismic Slip Interactions on a Subduction Megathrust, Guerrero, Mexico

合作研究：俯冲巨型逆冲断层的地震和非地震滑动相互作用，墨西哥格雷罗州

• 批准号: 0207820
• 负责人: Anthony Lowry
• 金额: $ 4.57万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2005-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0207820&HistoricalAwards=false
• 关键词: Collaborative; Research; Seismic; Aseismic; Slip

A transient event in Guerrero, Mexico, propagated from east to west along-strike, near the locking transition on the megathrust, and it affected the entire length of the Guerrero seismic gap over a period of months during early 1998. Campaign GPS data suggest the possibility that the 1998 Guerrero event is causally related to afterslip following the 1995 Mw=7.3 Copala earthquake. The Copala earthquake was located about 120 km east of the Guerrero gap, but afterslip appears to have propagated westward along-strike as much as 100 km during the first six months following the seismic rupture. Curiously, background seismic activity on the Guerrero megathrust unusually quiescent during the several months before, during and after the aseismic slip event, but returns to normal or above-normal levels several months after the transient ended. These observations raise several fundamental questions. First, did the Guerrero aseismic slip event really begin as afterslip following the Copala earthquake? Or is the occurrence of aseismic slip east of Acapulco in 1995-96 and west of Acapulco in 1998 merely coincidental? Secondly, how did the stress changes generated by these aseismic slip events influence seismic activity on the megathrust?This research project is examining these questions using JERS-1 InSAR data collected during the years 1994.2 to 1997.3 to estimate coseismic slip of the Copala event and postseismic afterslip in the region east of Acapulco. Also, strong ground motion seismic data from the Guerrero accelerograph network and broadband data from the Mexican regional network are being used to estimate earthquake source parameters from events with magnitude Mw7 that had never been examined previously. The events are being relocated using modern network differencing techniques, and the focal mechanisms, moment release, stress drops and other source parameters are also being characterized. The research team is combining the geodetic and seismic source to the slip history on the subduction megathrust during the past decade, and the associated change in Coulomb failure criteria as a function of time. The researchers are also assessing the space-time connection between Copala earthquake afterslip and the Guerrero slip transient, as well as the relationship between aseismic slip and seismic activity, using a model of nonlinear dynamic friction on the megathrust.

在墨西哥的Guerrero，一个短暂的事件沿着走向从东向西传播，靠近大型逆冲断层的锁定过渡，并在1998年初的几个月时间里影响了Guerrero地震间隙的整个长度。运动GPS数据表明，1998年格雷罗地震可能与1995年Mw=7.3的科帕拉地震后的余震有因果关系。科帕拉地震位于格雷罗断裂带以东约120公里处，但在地震破裂后的前六个月里，余震似乎沿走向向西传播了100公里。奇怪的是，在地震滑动事件之前、期间和之后的几个月里，格雷罗巨型逆冲断层的背景地震活动异常平静，但在地震滑动事件结束后的几个月里，背景地震活动又恢复正常或高于正常水平。这些观察结果提出了几个基本问题。首先，格雷罗地震滑动事件真的是从科帕拉地震后的余震开始的吗？或者1995- 1996年阿卡普尔科东部和1998年阿卡普尔科西部地震滑动的发生仅仅是巧合？其次，这些地震滑动事件产生的应力变化如何影响大型逆冲断层的地震活动？这个研究项目正在利用1994.2年至1997.3年收集的JERS-1 InSAR数据来研究这些问题，以估计Copala事件的同震滑动和阿卡普尔科以东地区的震后余震。此外，来自格雷罗加速网络的强地震动地震数据和来自墨西哥地区网络的宽带数据正在被用来估计以前从未检测过的Mw7级地震的震源参数。使用现代网络差分技术重新定位了这些事件，并对震源机制、力矩释放、应力降和其他源参数进行了表征。研究小组将过去10年的大地测量和地震震源与俯冲巨型逆冲断层的滑动历史相结合，并将库仑破坏准则的相关变化作为时间的函数。研究人员还利用大型逆冲断层的非线性动力摩擦模型，评估了Copala地震余震和Guerrero地震瞬变之间的时空联系，以及地震滑动和地震活动之间的关系。