Shear wave splitting beneath South Kamchatka during the 3-year period associated with the 1997 Kronotsky Earthquake
Shear wave splitting beneath South Kamchatka during the 3-year period associated with the 1997 Kronotsky Earthquake
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1997 年克罗诺茨基地震三年期间南堪察加半岛下方的剪切波分裂
DOI：
10.1016/j.tecto.2003.08.002
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发表时间：
2003
期刊：
影响因子：
2.9
通讯作者：
J. M. Lee
中科院分区：
文献类型：
--
作者：
M. Luneva;J. M. Lee
利用1996-1998年Kronotsky地震（M=7.7, 1997年12月5日）发生的3年间堪察加南部横波分裂测量资料，确定了俯冲带的各向异性参数和横波分裂随时间的变化。对Petropavlovskaya IRIS台站（PET）记录的局部小地震事件进行了分析。在N95±15°E范围内确定了3年期间快速横波极化的优势方位角，与太平洋板块总体运动方向一致。高速横波极化模拟表明，对称轴沿N15°E±10°方向的HTI模式对震源深度小于80 km的事件的观测资料拟合较好。对于较大的深度，不排除介质的正交对称性。各向异性系数随深度增大，地壳为1-2%，俯冲板块为4-7.5%。在阿瓦恰湾大地震系列（M≈5.5-7）之前和克罗诺茨基地震之前的1996-1997年间，时间延迟的变化表明普遍增加到10-15 ms/km。地幔事件的快速s波方位角分析揭示了时间周期变化。深度事件的快速方位角变化最规律，在3年周期中约为172天。地壳事件的快速极化表现得相对稳定。假定应力状态下的主要不稳定集中在下降板块，并影响上地幔和相对稳定的地壳。
Shear wave splitting measurements in South Kamchatka during the 3-year period (1996–1998) in which the Kronotsky Earthquake (M=7.7, December 5, 1997) occurred are used to determine anisotropic parameters of the subduction zone and shear wave splitting variations with time. The local small seismic events recorded at the Petropavlovskaya IRIS station (PET) were analyzed. The dominant azimuths of the fast shear wave polarizations for the 3-year period are defined within N95±15°E, which are consistent with the general Pacific Plate motion direction. Modeling of fast shear wave polarizations shows that HTI model with the symmetry axis oriented along N15°E±10° fit well the observed data for events the focal depths of which are less than 80 km. For the greater depths, the orthorhombic symmetry of medium is not excluded. The anisotropy coefficient increases generally with depth from 1–2% in the crust to 4–7.5% in the subducting plate. Variations in time delays show a general increase up to 10–15 ms/km during 1996–1997 before the large crustal earthquake series (M≈5.5–7) in the Avacha Bay and before the Kronotsky Earthquake. Analysis of fast S-wave azimuths of mantle events reveals a temporal cyclic variation. The most regular variations are observed for fast azimuths of deep events with a period of about 172 days over the 3-year period. The fast polarizations of crustal events behave comparatively stable. It is assumed that the major instabilities in stress state are localized in the descending slab and influenced the upper mantle and comparatively stable crust.