Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations
Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations
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DOI：
10.1029/2000jb000084
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发表时间：
2002-03
影响因子：
--
通讯作者：
F. Waldhauser;W. Ellsworth
中科院分区：
文献类型：
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作者：
F. Waldhauser;W. Ellsworth
[1]利用双差地震定位算法研究了加州海沃德断层沿线小规模地震活动与沿着大规模地壳断裂活动之间的关系。我们使用DD方法来确定1967年和1998年之间发生的地震活动的高分辨率震源位置。DD技术结合目录走时数据和来自波形互相关的相对P波和S波到达时间测量来解决事件之间的震源分离。重新定位的地震活动揭示了一个狭窄的，近垂直的断层带在大多数位置。这一地带沿着海沃德断层的北半部，然后在圣莱安德罗附近从它向东分叉，形成了Mission趋势。重新定位的地震活动性与卡拉维拉斯断层的滑动通过使命趋势转移到北方海沃德断层的想法一致。使命的趋势是没有明确的任何映射活动断层，因为它继续向南，并加入卡拉维拉斯水库的卡拉维拉斯断层。在某些位置，可以看到与主迹线相邻的离散结构，这些特征以前隐藏在网络位置的不确定性中。地震活动的精细结构表明，北方海沃德断层的断层面是弯曲的，或者地震发生在几个次级构造上。在圣莱安德罗附近，使命地震活动的更向西的趋势与（地震）南部海沃德断层的表面轨迹相交，地震活动在重新定位后仍然是分散的，相邻事件之间的震源机制变化很大，表明变形的高度断裂带。地震活动在空间上是高度有组织的，特别是在北方海沃德断层上，它形成水平的、滑动平行的震源条纹，宽度只有几十米，边界是几乎没有地震活动的地区。在1984年至1998年期间，当数字波形可用时，我们发现只有不到6.5%的地震可以被归类为重复地震，即同一断层片破裂一次以上的事件。这些最常见的是位于断层的浅蠕动部分，或在更深的条纹。在15年的观测期内，震级在M = 1.5左右的地震重复率很低，只有2 - 3次，这表明滑动速率很低或应力降很高。北方海沃德断裂面的大面积连续区域在15 - 10 km深度间隔内没有发生微地震，而这些深度处的地震活动集中表明，无震区要么被锁定，要么被延迟，并储存应变能，以便在未来的大规模地震中释放。
[1] The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggests that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital waveforms are available, we find that fewer than 6.5% of the earthquakes can be classified as repeating earthquakes, events that rupture the same fault patch more than one time. These most commonly are located in the shallow creeping part of the fault, or within the streaks at greater depth. The slow repeat rate of 2–3 times within the 15-year observation period for events with magnitudes around M = 1.5 is indicative of a low slip rate or a high stress drop. The absence of microearthquakes over large, contiguous areas of the northern Hayward Fault plane in the depth interval from ∼5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large-magnitude earthquakes.