Earthquakes and Slow Slip Events beneath the South Flank of Kilauea Volcano
Earthquakes and Slow Slip Events beneath the South Flank of Kilauea Volcano, Hawaii
Prof. Clifford H. Thurber,
University of Wisconsin-Madison
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. 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. 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.