Spatio-temporal variations of seismicity and coupling in the Himalaya

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。喜马拉雅山脉的大地变形主要反映了喜马拉雅逆冲断层(MHT)从地表向约15-20公里深度的锁定。当地的地震监测揭示了成群的地震活动，这可能是由锁定断裂带下倾边缘附近的应力积累所驱动的。而大地应变和地震活动分布的横向变化则表现出强烈的季节变化，反映了大地应变和地震活动上堆积的非均匀应力。这些可能是由陆地水储存变化引起的，主要是在恒河平原，但也可能有其他原因。因此，我们提出利用尼泊尔和西藏南部的连续GPS(CGPS)数据和尼泊尔国家地震台网记录的地震活动来分析尼泊尔喜马拉雅地区大地应变和地震活动的空间格局和时间演化。该项目的主要目标是(1)确定主要喜马拉雅冲断带(MHT)的锁定模式，(2)评估地震间应变积累与地震活动之间的关系，(3)确定应变随时间变化的原因，(4)分析地震活动与应变率之间的关系，并得出地震成核的含义。该项目将有助于限制为尼泊尔喜马拉雅地区未来地震做准备的应力聚集的时空模式。它将促进我们对物理参数的理解，这些参数决定了断层是稳定地爬行还是具有粘滑运动，从而产生重复的地震滑动事件。它还将促进我们对地震成核的理解。该项目将有助于提供有关尼泊尔和印度北部地震危险的重要信息。事实上，喜马拉雅大地震的频率严重依赖于地震间隔期滑动赤字的累积速度。此外，滑动亏损的空间模式可能是不均匀的，可能会影响到许多俯冲带所推断的大地震破裂。这个项目将解决地震构造学中最具挑战性的问题：为什么特定的断层部分会爬行或产生地震？地震活动率如何与震间应变积累和其他应力波动来源(固体潮、积雪负荷、陆地水储存)有关。最后，该项目将促进国际科学合作，并将构成博士研究项目的核心。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Geodetic deformation across the Himalaya reflects primarily locking of the Main Himalayan Thrust (MHT) fault from the surface to a depth of about 15-20km. Local seismic monitoring has revealed clustered seismicity that is probably driven by stress accumulation near the downdip edge of the locked fault zone. The pattern of geodetic strain and the distribution of seismicity show however lateral variations which could reveal heterogeneous stress build up on the Also both geodetic strain and seismicity show strong seasonal variations. These may be induced by landwater storage variations, mostly in the Gangetic plain, but other causes may also be advocated. We therefore offer to analyze the spatial pattern and temporal evolution of geodetic strain and seismicity in the Nepal Himalaya using data from Continuous GPS (CGPS) from Nepal and southern Tibet, and seismicity recorded by the National Seismic Network of Nepal. The main objectives of this project are to(1) determine the pattern of locking on the Main Himalayan Thrust (MHT),(2) assess the relationship between interseismic strain build up and seismicity,(3) determine the cause of temporal changes of strain,(4) analyze the relationship between seismicity and strain rates and derive implications for earthquake nucleation.The project will help constrain the spatio-temporal pattern of stress build up that is preparing future earthquakes in the Nepal Himalaya. It will advance our understanding of the physical parameters that determine whether a fault creeps steadily or has a stick-slip motion producing repeating seismic slip events. It will also advance our understanding of earthquake nucleation.The project will contribute important information regarding seismic hazard in Nepal and northern India. Indeed, the frequency of large earthquakes in the Himalaya depends critically on the rate at which deficit of slip accumulates in the interseismic period. Also the spatial pattern of deficit of slip is probably heterogeneous and might influence large earthquake ruptures as has been inferred for a number of subduction zones.This project will address most challenging questions in seismotectonics: why does a particular fault portion creeps or produces earthquakes? How does seismicity rate relates to interseismic strain buildup and to other sources of stress fluctuations (earth tides, snow loading, landwater storage.) Finally, the project will foster international scientific collaboration and will constitute the core of a PhD research project.