Study of Postseismic Deformation Due to the 2010 M7.2 El Mayor (Mexico) Earthquake

2010年4月4日，美国-墨西哥边境发生的里氏7.2级市长地震是过去18年来袭击南加州的最大地震。该项目的主要目标是：(1)使用动态GPS观测准确捕捉地震后的瞬时形变；(2)使用精确的大地测量，包括连续/动态GPS和InSAR数据，以确定地震后松弛所涉及的物理机制。关于上发震地壳和下伏韧性基底之间的耦合性质，存在着激烈的争论。震间变形的端元模型包括下地壳(可能还有上地幔)局部剪切带对地壳断层的“自下而上”加载和同震应力变化对粘性基底的“自上而下”加载。一个相关的问题是，什么样的流变学最好地描述了脆韧性转变之下的岩石。相互竞争的观点包括线性麦克斯韦、标准线性固体、双线性、幂定律等。这些问题对于我们理解地震后的应力变化、地震活动的延迟触发以及大陆岩石圈的长期强度具有重要的意义。对El Mayor M7.2级地震引起的震后变形的调查为这些问题提供了新的见解，并允许对相互竞争的假设进行强有力的测试。

The April 4, 2010, M7.2 El Mayor earthquake on the US-Mexico border was the largest earthquake to strike Southern California in the last 18 years. The main goals of this project are (1) to accurately capture the transient deformation following the earthquake using campaign GPS observations and (2) use precise geodetic observations, including continuous/campaign GPS and InSAR data to identify the physical mechanisms involved in postseismic relaxation. There is a vigorous debate about the nature of coupling between the upper seismogenic crust and the underlying ductile substrate. End-member models of interseismic deformation include ``bottom-up'' loading of crustal faults by localized shear zones in the lower crust (and perhaps upper mantle) and ``top-down'' loading of the viscous substrate by coseismic stress changes. A related question is what rheology best describes rocks below the brittle-ductile transition. Competing views include linear Maxwell, standard linear solid, bi-linear, powerlaw etc. rheologies. These questions have fundamental implications for our understanding of post-earthquake stress changes, delayed triggering of seismicity, and long-term strength of the continental lithosphere. Investigation of postseismic deformation due to the M7.2 El Mayor earthquake is offering new insights into these questions and allowing a robust test of the competing hypotheses.