Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event
Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event
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DOI：
10.1785/bssa0800030507
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发表时间：
1990-06
影响因子：
3
通讯作者：
J. Mori;S. Hartzell
中科院分区：
文献类型：
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作者：
J. Mori;S. Hartzell
我们研究了短周期P波，以调查波形数据是否可以用来确定两个节面中的哪一个是加州Upland附近的一次小(ML4.6)地震的实际断裂面。我们通过选择一次小余震(ML 2.7)作为经验格林函数，消除了路径和位置的并发症。利用经验格林函数对主激波P波进行反卷积，产生简单的远场位移脉冲。我们用最小二乘法对这些脉冲进行了反演，得到了有限断层上的滑移分布。在不同破裂速度下，对震源机构的两个节面(走向125°，倾角85°和走向221°，倾角40°)进行了测试。西南向断层面比东南向断层面提供了更好的拟合解。我们测得的力矩为4.2×1022达因厘米。破裂速度和震源区不能很好地分辨，但如果我们假设合理的破裂速度是横波速度的0.87倍，我们得到的震源面积为0.97km2，应力降为38bar。南西向断层面的选择与横断岭前缘断裂带附近部分的走向一致，并指示了左旋运动。该方法为无地表破裂、余震位置无明显趋势的小震提供了一种确定断裂面的方法。
We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.