Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California
Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California
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DOI：
10.1002/2017gl072612
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发表时间：
2017-06-16
影响因子：
5.2
通讯作者：
Yule, Doug
中科院分区：
文献类型：
--
作者：
Heermance, Richard V.;Yule, Doug
加利福尼亚州南部的圣戈戈尼奥山口(SGP)包含一个40公里长的构造复杂区域，圣安德烈亚斯断层(SAF)在这里分叉成一系列滑动历史未知的斜滑断层。我们结合了新的Be-10暴露年龄(Qt4：8600(+2100，-2200)年和Qt3：5700(+1400，-1900)年B.P.)放射性碳年龄(126060年B.P.)从晚全新世阶地与这些表面的陡峭位移，记录了两个断层的全新世滑动速率为5.7(+2.7，-1.5)毫米/年。我们的首选滑移率是SGP以外的SAF(即科切拉山谷和圣贝纳迪诺段)沿线平均滑移率的37-49%，这意味着应变在该地区从SAF转移出去。这里的地震最有可能发生在非常大的、贯穿SAF的事件中，其复发率低于SAF的其他地方，因此只有大约三分之一的SAF破裂穿透或起源于通道。简单语言摘要圣安德烈亚斯断层南部的地震有多大？这个问题的答案取决于地震是只沿着个别断层段，如棕榈泉以北的科切拉山谷段，还是跨越多个段，包括通过圣戈戈尼奥山口的区域。我们已经确定了圣戈戈尼奥山口内断层河流沉积的年龄和偏移量，以记录这些断层在过去1万年中的滑动速率。我们的结果表明，该地区的长期滑动速率接近6毫米/年，几乎是该地区东部和西部滑动速率的1/2。这些新的速率，再加上断裂的地貌表面，意味着大震级地震偶尔会导致圣安德烈亚斯断层从索尔顿海到莫哈韦沙漠300公里长的断裂。尽管沿着圣安德烈亚斯断层南部的许多地震(类似于65%)很可能不会穿过这个山口，但我们的新结果表明，圣安德烈亚斯断层南部可能发生7.5级大地震，可能每1000-1500年发生一次。
The San Gorgonio Pass (SGP) in southern California contains a 40km long region of structural complexity where the San Andreas Fault (SAF) bifurcates into a series of oblique-slip faults with unknown slip history. We combine new Be-10 exposure ages (Qt4: 8600 (+2100, -2200) and Qt3: 5700 (+1400, -1900)years B.P.) and a radiocarbon age (126060years B.P.) from late Holocene terraces with scarp displacement of these surfaces to document a Holocene slip rate of 5.7 (+2.7, -1.5)mm/yr combined across two faults. Our preferred slip rate is 37-49% of the average slip rates along the SAF outside the SGP (i.e., Coachella Valley and San Bernardino sections) and implies that strain is transferred off the SAF in this area. Earthquakes here most likely occur in very large, throughgoing SAF events at a lower recurrence than elsewhere on the SAF, so that only approximately one third of SAF ruptures penetrate or originate in the pass.Plain Language Summary How large are earthquakes on the southern San Andreas Fault? The answer to this question depends on whether or not the earthquake is contained only along individual fault sections, such as the Coachella Valley section north of Palm Springs, or the rupture crosses multiple sections including the area through the San Gorgonio Pass. We have determined the age and offset of faulted stream deposits within the San Gorgonio Pass to document slip rates of these faults over the last 10,000years. Our results indicate a long-term slip rate of similar to 6mm/yr, which is almost 1/2 of the rates east and west of this area. These new rates, combined with faulted geomorphic surfaces, imply that large magnitude earthquakes must occasionally rupture a 300km length of the San Andreas Fault from the Salton Sea to the Mojave Desert. Although many (similar to 65%) earthquakes along the southern San Andreas Fault likely do not rupture through the pass, our new results suggest that large >M-w 7.5 earthquakes are possible on the southern San Andreas Fault and likely occur every 1000-1500years.