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Coseismic and Postseismic Deformations From Great 2006-2007 Kuril Earthquakes Revealed by Regional GPS Observationsтезисы доклада
- Авторы: Steblov G.M., Kogan M.G., Levin B.V., Vasilenko N.F., Prytkov A.S., Frolov D.I.
- Сборник: American Geophysical Union (AGU) 2007 Fall Meeting
- Серия: Eos, Transactions American Geophysical Union
- Том: 88
- Тезисы
- Год издания: 2007
- Издательство: AGU Publications
- Местоположение издательства: Вашингтон
- Первая страница: G13A-0916
- Аннотация: he 1200-km long Kuril arc is the last subduction zone never previously explored by space geodetic methods. In 2006, we installed the continuous GPS network (CGPS) over the whole arc and added several survey-mode stations (SGPS). In 2006-2007, the paired great earthquakes near the central Kurils happened several months after we installed the network: Mw 8.3, Nov. 15, 2006 underthrusting event, and Mw 8.1, Jan. 13, 2007 tensional outer-rise event. Although the earthquakes have prevented us from estimating reliable interseismic surface velocities for most of the Kuril arc, it has given us the chance to examine great earthquakes and their transient response in the region that was a seismic gap for a century. Two SGPS stations nearest to the hypocenters captured the largest observed offsets of about 0.6 m reflecting the superposed effect of both events. These offsets are mostly attributed to the Nov. 2006 event. More distant stations captured coseismic offsets caused by each event ranging from several mm to 60 mm. Significant transient signals associated with rapid postseismic afterslip in the rupture or with the relaxation in the viscous mantle were noticed for the Nov. 2006 event but not for the Jan. 2007 event. Large amount of afterslip was observed in the first 12 hours following the Nov. 2006 main shock. For both events, we inverted observed GPS offsets to evaluate the size and rake of the coseismic slip. In forward modeling, the PREM layered model of the spherical Earth was adopted (the method of F. Pollitz). The rupture dimensions and geometry were constrained by the spatial distribution of aftershocks, shallow seismicity, plate tectonics considerations, and CMT solutions. In case of the Jan. 2007 event, plate tectonic constraints are inapplicable. To ensure correct estimation of the Nov. 2006 coseismic offsets, we modeled postseismic transients by the logarithmic approximation in agreement with the rate-strengthening friction. For the Nov. 2006 event, our geodetic estimate of the slip with the preferred rupture geometry is 3.3 m. For Jan. 2007 event, we prefer the CMT fault plane with the strike parallel to the trench; however, the estimates of slip for both CMT fault planes are nearly identical: 3.2 and 3.5 m. Geodetically estimated rakes agree with those of CMT within 18 degrees. Geodetic coseismic moments were estimated with the commonly adopted crustal shear modulus of 30 GPa. For both earthquakes, the geodetic moments are about twice smaller than CMT moments. The only plausible way to make the geodetic and CMT moments agree is to assume a higher shear modulus. GPS time series during 7.5 month following the Nov. 2006 event show that the Kuril GPS stations are moving to SE, opposite to the direction of interseismic motion. Whether the observed drift reflects the postseismic afterslip or the viscous relaxation in the mantle can be determined from the future observations.
- Добавил в систему: Стеблов Григорий Михайлович