1:45 PM - 2:00 PM
[SCG45-49] Geological evidence for fast earthquakes on the Milun Fault, Taiwan
★Invited Papers
Keywords:MiDAS, frictional heating, strain localization, lime, fast earthquake
Earthquakes are common natural phenomena in Taiwan, especially in the city of Hualien. The Milun fault in Hualien City ruptured in 1951 and was triggered by the 2018 Mw 6.4 Hualien earthquake, presumably as an active fault with a short recurrence interval. However, the fault zone characteristics of the Milun fault remain largely unknown due to the lack of an exposed fault zone. The Milun fault Drilling and All-inclusive Sensing (MiDAS) project was designed to penetrate the active fault zone of the Milun fault and deploy multiple monitoring systems. Here, we characterize the Milun fault zone sampled by MiDAS using microanalytical methods, including optical microscopy, scanning and transmission electron microscopy (SEM and FIB-TEM), in-situ synchrotron X-ray diffraction, and Raman spectroscopy.
Results show that the Milun fault zone is surrounded by the Milun conglomerate in the hanging wall and footwall. The Milun fault zone consists of variable widths of anastomosing clay-rich zones within spotted schists and dark gray gouges characterized by multiple black gouge layers. Both the dark gray gouges and the black gouge layers contain quartz, feldspar, carbonates, chlorite, kaolinite, and illite. In particular, the black gouge contains glassy materials. Fibrous minerals, as thermal decomposition products of carbonate (lime; CaO), are observed in small localized patches (~ a few hundred microns in size) within the black gouge. The presence of both glassy materials and lime suggests the coexistence of strain localization and frictional heating. In addition, since lime is an unstable mineral, the presence of lime suggests that the black gouge layers were recently sheared and preserved under dry conditions. We propose that the black gouge layers are the result of a fast earthquake, including the 2018 Mw6.4 Hualien earthquake.
Results show that the Milun fault zone is surrounded by the Milun conglomerate in the hanging wall and footwall. The Milun fault zone consists of variable widths of anastomosing clay-rich zones within spotted schists and dark gray gouges characterized by multiple black gouge layers. Both the dark gray gouges and the black gouge layers contain quartz, feldspar, carbonates, chlorite, kaolinite, and illite. In particular, the black gouge contains glassy materials. Fibrous minerals, as thermal decomposition products of carbonate (lime; CaO), are observed in small localized patches (~ a few hundred microns in size) within the black gouge. The presence of both glassy materials and lime suggests the coexistence of strain localization and frictional heating. In addition, since lime is an unstable mineral, the presence of lime suggests that the black gouge layers were recently sheared and preserved under dry conditions. We propose that the black gouge layers are the result of a fast earthquake, including the 2018 Mw6.4 Hualien earthquake.