地    点：海洋与地球科学学院215
时    间：2012年5月14日（周一）14:00-15:00 PM
联系人：天然地震与地球动力学组 薛梅（15021975216

 

报告人背景：Cliff Thurber 教授在三维地震层析成像领域的研究在国际上具有影响力。他的主要研究兴趣是对断层、火山和俯冲带进行地震层析成像，他的长期的研究区域是加州中部的圣安德烈斯断层、夏威夷和阿拉斯加的火山。另外，他对地震定位和地球物理反演理论和核爆监测也有深入研究。

报告摘要：In November 1975, a magnitude 7.2 earthquake struck southern Hawaii, with an epicenter and aftershock zone beneath the subaerial part of the South Flank of Kilauea Volcano. Geodetic observations showed that the South Flank shifted up to 8 meters seaward and subsided as much as 3.5 meters. The focal mechanism of the main shock indicated a near-horizontal fault plane. The nature of this earthquake and the geometry and depth of the fault on which it occurred are issues that have been debated for decades. In the decades since, the South Flank has continued to shift seaward, in places as fast as 10 cm per year. In 2000, a slow slip event was first observed at Kilauea, with a duration of about 36 hours and an equivalent magnitude of 5.7. It was located in the same general area as the 1975 earthquake and triggered small earthquakes, but the modeled fault for the slow slip event was off-shore and surprisingly shallow compared to South Flank microseismicity. Since then, a number of other slow slip events have been identified, occurring every 2 to 3 years with somewhat variable size. In January 2007, a dense deployment of temporary seismic and geodetic instruments was set up on the South Flank to try to capture the next expected slow slip event, and attempt to observe nonvolcanic tremor that has been found to accompany slow slip events elsewhere in the world, mainly at subduction zones. On June 18, a strong magmatic intrusion occurred in Kilauea's East Rift Zone. Careful geodetic analysis revealed that the intrusion was followed by a slow slip event, but strong volcanic tremor made it impossible to observe any nonvolcanic tremor that may have occurred. A well-constrained fault model for the slow slip event was determined with the enlarged geodetic dataset, and the temporary seismic array data permitted the estimation of rather precise locations for the seismicity triggered by the slow slip event. The results show that the slow slip event and the triggered microseismicity lie on a deep subhorizontal fault that is the same fault on which background seismicity, and presumably Kalapana-type main shocks, occur, resolving the previous seismic-geodetic discrepancy. In 2010, another slow slip event occurred, this time without a concurrent intrusion, but the search for nonvolcanic tremor using sparse permanent network stations was unsuccessful. At the present time, another very dense seismic array is in place on Kilauea's South Flank, awaiting the next slow slip event. We are optimistic that, if nonvolcanic tremor does occur in concert with Kilauea's slow slip events, this array will detect it. If not, Kilauea will be unique in the world in having repeating slow slip events but no nonvolcanic tremor.