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

Korren Caitlyn S, Bedford NY

Investigators

Abstract

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.