EAPSI: Seismic faulting causes rocks to melt and capture earthquake parameters

巨大的地震震撼了世界。1999年发生的里氏7.6级集集地震夺走了数千人的生命，给台湾造成了数十亿美元的损失。台湾毁灭性地震的历史表明，该地区是世界上地震最活跃的地区之一。欧亚板块和菲律宾板块的碰撞，在台湾东侧形成了两个俯冲带。碰撞过程产生了巨大的压力，后果包括毁灭性的地震。在地震期间，岩石相互滑动，导致破碎、研磨和熔化，形成一种被称为假硅质岩的岩石。为了更好地了解地震，将收集和分析假地震。最近在台湾希望河沿岸发现了一个新的假黄晶石产地。这些4.1MYO假快速陨石保存着有关震级和滑动发生方式的信息。台湾师范大学与叶恩超博士合作，在希望河取样将产生假玄武岩，以供3D模型和磁学分析。本研究的主要目的是确定假玄武岩矿脉是来自单一滑动事件还是来自多个滑动事件，并在三维中分析和模拟静脉几何形状(以推断断层面的产状)、平均脉厚度、滑动事件的大小(S)和滑动方向(S)。这需要高分辨率的映射和定向样本的收集。层析分析需要图像来构建3D模型。假玄武岩生成脉的宽度与地震震级大致成正比。注入静脉和生成静脉之间的夹角主要反映了法向应力和剪切应力之间的比率。此外，测量这些假玄武岩中的磁性矿物取向可以得到同震滑动运动学。这些技术将有助于评估古代地震的震源机制和震级，从而更好地了解台湾目前的地震风险。这项NSF EAPSI奖是与台湾国家科学委员会合作资助的。

Large magnitude earthquakes rattle the world. The MW 7.6 1999 Chi-Chi earthquake claimed thousands of lives and cost Taiwan billions of dollars. Taiwan's history of devastating earthquakes nominates this region as one of the world's most seismically active areas. The collisions of the Eurasian and Philippine plates, forms two subduction zones on the eastern side of Taiwan. The collision process causes immense stresses with consequences including devastating earthquakes. During an earthquake, rocks slip against one another causing crushing, grinding and melting forming a rock called a pseudotachylyte. To better understand earthquakes, pseudotachylytes will be collected and analyzed. A new pseudotachylyte locality was recently discovered along the Hoping River in Taiwan. These 4.1 M.y.o. pseudotachylytes hold information on the magnitude and how sliding occurred. Sampling at the Hoping River will yield pseudotachylyte for analysis by 3D model and magnetics at National Taiwan Normal University in collaboration with Dr. En-Chao Yeh.The principal objectives of this study are to determine if the pseudotachylyte veins originate from single or multiple slip events, analyze and model vein geometry in 3-D (to infer the attitude of the fault plane), average vein thickness, magnitude of the slip event(s) and direction of slip(s). This requires high resolution mapping and the collection of oriented samples. A tomographic analysis requires images for building a 3D model. The width of a pseudotachylyte generation vein is broadly proportional to earthquake magnitude. The angle between injection veins and the generation vein primarily reflects the ratio between normal and shear stresses. Furthermore, measuring the magnetic minerals orientations in these pseudotachylytes can yield coseismic slip kinematics. Together these techniques will aid in assessing focal mechanism and magnitude of an ancient earthquake leading to a better understanding of Taiwan's present seismic risk. This NSF EAPSI award is funded in collaboration with the National Science Council of Taiwan.