S41B-2760
The footprints of typhoons on seismic records and their implications on small-scale coupling mechanisms in South China Sea
Thursday, 17 December 2015
Poster Hall (Moscone South)
Han Xiao1, Mei Xue1, Ting Yang1, Chenguang Liu2, Qingfeng Hua2, Shaohong Xia3, Haibo Huang3, Ba Manh Le1, Da Huo1, Mohan Pan1 and Lin Li1, (1)Tongji University, Shanghai, China, (2)The First Institute of Oceanography, State Oceanic Administration, Qingdao, China, (3)SCSIO South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China
Abstract:
By investigating the footprints of typhoons on seismic records, we can understand their contributions to seismic noises as well as to small-scale coupling mechanisms of typhoon-land and typhoon–ocean–land. We analyze the signatures of typhoon KAI-TAK and BOPHA using seismic data from the ocean-bottom seismometers (OBSs) deployed in the central basin of South China Sea by Tongji University in 2012 as well as seismic stations (IC.QIZ,HK.HKPS and RM.SZP) on lands.Our preliminary results show that typhoons mainly enhance microseisms at the frequency band of ~0.1–0.5 Hz, including both long period double frequency (LPDF) and short period double frequency (SPDF) microseisms. A positive correlation observed between the amplitude of microseisms and the height of local ocean waves. Because OBSs are deployed at the bottom of ocean, single frequency (SF) microseisms are not prominent on them due to their fast attenuation with depth. During the typhoon KAI-TAK, the increase of LPDF energy is very small in OBSs while that is very high on land stations, indicating that LPDF microseisms are generated at nearby shorelines and can propagate towards the sea through the solid earth. However, the increase of SPDF energy is almost the same level for both OBSs and land stations indicating that the generation of SPDF is probably local.However, we also observe a small amount of energy arrives before the increases of the wave heights at the land station HK.HKPS. We derive that this energy may from a source that is not local: while LPDF can be generated at nearby shorelines and SPDF can be generated everywhere locally, they can both transmit through the solid part of the Earth to a station some distance away, i.e. HK.HKPS. In addition, we find that typhoons enhance not only the microseisms as expected but also the seismic energy from higher frequency bands. The spectrum amplitude during Typhoon periods, normalized by that of no-storm periods, shows that land stations produce stronger higher frequency seismic waves than OBSs.This may reflect a difference of coupling mechanisms between typhoon-land and typhoon–ocean–land, which we are further investigating.
