A study of microseisms induced by typhoon nanmadol using ocean-bottom seismometers

From the end of August to early September 2011, 15 ocean-bottom seismometers (OBSs) were deployed offshore northeastern Taiwan for approximately 20 days. During this period, the typhoon Nanmadol formed in the western Pacific, moved northwestward from the East Philippines, and made landfall on the island of Taiwan. In this study, we analyzed the seismic signals from the OBSs and the marine metrological data to investigate the influence of the typhoon on submarine seismic records. Our results show that the signals induced by the typhoon occurred mainly at approximately 0.15–0.5 Hz frequency. The magnitude of these signals depends substantially on water depth. Some exceptions, most likely generated by site effects, were observed. Also, a positive correlation exists between the signals energy and the local wave height, which suggests that the microseisms were affected by the pressure changes produced by the local wave activity as the typhoon passed over the stations. However, when an OBS was outside the typhoon periphery, any wave energy variations could only be caused by the elastic wave formed around the typhoon area, the energy of which is transmitted through the ocean bottom to the stations. Thus, no local waves were excited by the strong winds, and only a relatively small amount of energy was recorded.