Microseismicity around rupture area of the 1944 Tonankai earthquake from ocean bottom seismograph observations     

Koichiro Obana  Shuichi Kodaira  Yoshiyuki Kaneda 《Earth and Planetary Science Letters》2004,222(2):561-572

Along the Nankai trough, southwestern Japan, the Philippine Sea plate (PSP) is subducting beneath the Eurasian plate, and large interplate earthquakes have occurred repeatedly with a recurrence interval of about 100-200 years. The most recent large thrust event in the eastern Nankai trough off Kii Peninsula was the 1944 Tonankai earthquake. In this region, current seismicity is very low and hypocenters are not determined accurately by the land seismic network. We conducted microseismicity observations around the rupture area of the 1944 Tonankai earthquake using ocean bottom seismographs (OBSs). Hypocenters were determined using a 2-D seismic velocity structure model based on an airgun-OBS seismic survey. Results obtained show that the seismicity was relatively active near the trough axis. These earthquakes may relate to deformation of the subducting Philippine Sea plate. On the other hand, microseismicity in the rupture area of the 1944 Tonankai earthquake was very low. This low-level seismic activity in the co-seismic rupture area of the 1944 Tonankai earthquake likely relates to a single large asperity off Kii Peninsula.  相似文献   

Geochemical characteristics of ores and surface waters for environmental risk assessment in the Pinpet iron deposit,southern Shan State,Myanmar     

Kyaw Zay Ya  Tsubasa Otake  Aoi Koide  Kenzo Sanematsu  Tsutomu Sato 《Resource Geology》2020,70(3):296-308

Mining operations in the Pinpet Fe deposit, which is the second‐largest Fe deposit in Myanmar, are currently suspended, in part because of possible contamination of heavy metals and hazardous elements (e.g., Fe, As, Cu, Zn, and U) into the surrounding aquatic environment and associated public concern. However, a scientific investigation of the source and degree of contamination in streams near the deposit has not yet been conducted. Therefore, we quantified heavy‐metal and hazardous‐element concentrations of stream waters and sediments in stream beds, and measured the speciation and concentration of these metals in deposit Fe ores using the sequential extraction method, to better understand the influence of mining activities on the surrounding environment. Geochemical results for Nan‐tank‐pauk stream and its tributaries indicate that the chemical compositions of their waters are controlled by carbonate bedrock and that no detectable contamination has occurred as a result of mining activity or hematite and limonite ore beneficiation processes in either the wet or dry seasons. All measured heavy‐metal and hazardous‐element concentrations were below the World Health Organization standards for drinking water and the proposed national drinking water quality standards in Myanmar. Bulk chemical compositions of stream‐bed and tailings dam sediments show that As, Zn, and Cu concentrations are similar to those in uncontaminated sediments. Results of bulk mineralogical and chemical analyses of ore samples reveal that some limonite ore samples contain substantial amounts of As (up to 2 wt%). However, sequential extraction results indicate that most (>90%) of the As in these As‐rich ores is hosted in insoluble fractions (e.g., crystalline Fe hydroxides and clays). Therefore, arsenic is unlikely to be released into the aquatic environment by interacting with water during ore beneficiation processes should the mine resume operations.  相似文献