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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Shallow structure of the Landers fault zone from explosion-generated trapped waves
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Shallow structure of the Landers fault zone from explosion-generated trapped waves

机译：爆炸产生的捕获波在兰德斯断层带的浅层构造

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摘要

With fault-zone trapped waves generated by near-surface explosions within the fault zone of the 1992 Landers, California, earthquake and recorded by linear seismic arrays deployed along and across the fault, we have delineated the shallow seismic structure near the 30-km-long southern rupture on the Johnson Valley fault. The explosion-excited trapped waves with relatively large amplitude and long-duration wave train after the S waves are similar to those generated by aftershocks [Li et al., 1994a, b] but have lower frequencies and travel more slowly. Coda-normalized amplitude spectra of explosion-excited trapped waves show a maximum at approx 2 Hz, which decreases rapidly with the station offset from the fault trace on the cross-fault profiles. Normalized amplitudes of trapped waves on the along-fault profile also decreased with distance between the explosion and station, giving an apparent Q of approx 18 at 1-2 Hz in the fault zone for the shot near the profile. THe dispersion of trapped waves from 0.6 to 2.5 Hz recorded on this along-fault profile implies a shear velocity of approx 1.0 km/s for the fault zone and approx 1.8 km/s for the wall rock, while the data from the farther shot show an increase in velocity and Q with depth. Measured group velocities and Q values were used as constraints in the numerical modeling of trapped waves on cross-fault and along-fault profiles. Results reveal that the shallow Johnson Valley fault is marked by a zone 250 m wide where the shear velocity is 1 km/s and Q is 20. Calculation of finite difference synthetics for a depth-varying fault structure show that these model parameters apply to the depth of approx 1 km, below which the fault zone shear velocity increases to 1.9 km/s and Q increases to 30.
机译：利用1992年加利福尼亚州兰德斯地震的断层带内近地表爆炸产生的断层带捕获波，并通过沿断层带和跨断层部署的线性地震阵列进行记录，我们划定了30 km-附近的浅层地震结构约翰逊谷断裂带上长期的南部破裂。 S波后爆炸激发的陷波具有较大的振幅和较长的波列，类似于余震产生的陷波[Li等，1994a，b]，但频率较低，传播速度较慢。爆炸激发陷波的尾波归一化振幅谱在约2 Hz处显示最大值，并且随着站点从交叉故障剖面上的故障迹线偏移而迅速减小。沿断层剖面的捕获波的归一化幅度也随着爆炸和测站之间的距离而减小，在断层附近，对于剖面附近的散布，在1-2 Hz处的表观Q约为18。沿断层剖面记录的0.6至2.5 Hz陷波的频散表明，断层带的剪切速度约为1.0 km / s，围岩的剪切速度约为1.8 km / s，而远距离拍摄的数据表明速度和Q随着深度增加。在跨断层和沿断层剖面的陷波数值模拟中，将测得的群速度和Q值用作约束条件。结果表明，Johnson Valley浅层断层以250 m宽的区域为标志，剪切速度为1 km / s，Q为20。对深度变化型断层结构的有限差分合成计算表明，这些模型参数适用于大约1 km的深度，低于该深度时断层带的剪切速度增加到1.9 km / s，Q增加到30。

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