EAR-PF: The spatiotemporal scales of transient slow slip on the San Andreas fault near San Juan Bautista, central California, and the implications for seismic hazard

EAR-PF：加利福尼亚州中部圣胡安包蒂斯塔附近圣安德烈亚斯断层上瞬态慢滑移的时空尺度及其对地震灾害的影响

• 批准号: 2053997
• 负责人: Heather Shaddox
• 金额: $ 17.4万
• 依托单位: Shaddox, Heather R
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2053997&HistoricalAwards=false
• 关键词: EAR; PF; spatiotemporal; scales; transient

Dr. Heather Shaddox has been awarded an NSF EAR Postdoctoral Fellowship to combine seismic and geodetic observations to characterize the nature of fault slip and earthquake hazard for the San Andreas fault near San Juan Bautista in central California. This work will be conducted at University of California Berkeley in collaboration with mentor Roland Burgmann. Slip on faults occurs as a spectrum, ranging from slow, continuous sliding (i.e., aseismic slip) to rapid movement during earthquakes (i.e., seismic failure). Aseismic slip can temporarily relieve stress on a fault but may also trigger large, damaging earthquakes on adjacent segments of the fault. Therefore, detecting and understanding this temporary release of stress (called aseismic slip transients) is key in seismic hazard evaluation and has direct societal impacts. Because aseismic slip transients do not generate seismic waves, geodetic instruments like land Global Positional System (GPS) stations with observational limits are required to detect these movements. This project will use related small earthquakes (microseismicity) to infer the location of aseismic slip transients, taking advantage of existing and newly installed instrumentation to create a catalog of seismicity at unprecedented resolution. The results of this project will provide information about spatial and temporal scales of fault slip and have implications for determining seismic hazard. This detailed analysis may also uncover answers to fundamental fault slip questions including how often aseismic slip precedes earthquakes and how often earthquakes trigger aseismic slip transients. We can also gain insights into other tectonic environments where direct observations are limited (e.g., the offshore portion of subduction zones) by studying this natural laboratory. This project also involves educational materials about earthquakes for elementary school students in the San Francisco Bay Area of California, a region with high seismic hazards. The general objective of this project is to study the spatiotemporal scales of transient aseismic slip on the San Andreas fault near San Juan Bautista in central California at unprecedented resolution to ultimately gain a broader understanding of the nature of fault slip. San Juan Bautista, located at the northwest boundary of the creeping section of the San Andreas fault and the southeast termination point of the Mw 7.9 1906 San Francisco earthquake, forms a creeping-to-locked transition of the fault. The dense instrumentation and historic record of transient aseismic slip near San Juan Bautista make it an excellent natural laboratory to study the interplay of seismic and aseismic slip. We will create a catalog of spontaneous and trigged aseismic slip transients on the San Andreas fault near San Juan Bautista by combining seismic (general seismicity, near-repeating earthquakes) and geodetic (cGPS, InSAR, borehole strainmeter, creepmeter) observations to help answer the following questions: What is the spatial scale, temporal scale, and magnitude of aseismic slip transients? How often and by what mechanism(s) does aseismic slip lead to small and moderate-sized earthquakes? How often do these earthquakes lead to aseismic slip? Based on the scales of transient aseismic slip, is the San Andreas fault near San Juan Bautista capable of large (Mw 6) earthquakes? We will further study the relationship between shallow and deep aseismic slip, spatiotemporal changes in creep rate in this locking transition, and evaluate the utility of near-repeating earthquakes as a proxy for transient aseismic slip. We additionally hope to gain insights into other tectonic environments, particularly the offshore portion of subduction zones where direct observations are limited, by studying this natural laboratory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Heather Shaddox 博士获得了 NSF EAR 博士后奖学金，以结合地震和大地测量观测来描述加利福尼亚州中部圣胡安包蒂斯塔附近圣安德烈亚斯断层的断层滑移和地震危险的性质。 这项工作将在加州大学伯克利分校与导师 Roland Burgmann 合作进行。断层上的滑动以一系列形式发生，从缓慢、连续的滑动（即抗震滑动）到地震期间的快速移动（即地震破坏）。抗震滑移可以暂时缓解断层上的应力，但也可能在断层的邻近部分引发大规模的破坏性地震。因此，检测和理解这种暂时的应力释放（称为抗震滑移瞬态）是地震危险性评估的关键，并且具有直接的社会影响。由于地震滑动瞬变不会产生地震波，因此需要具有观测限制的陆地全球定位系统 (GPS) 站等大地测量仪器来检测这些运动。该项目将利用相关的小地震（微震活动）来推断地震滑动瞬变的位置，利用现有和新安装的仪器以前所未有的分辨率创建地震活动目录。该项目的结果将提供有关断层滑动的空间和时间尺度的信息，并对确定地震危险性具有影响。这种详细的分析还可能揭示基本断层滑动问题的答案，包括地震发生前地震滑动的频率以及地震触发地震滑动瞬变的频率。通过研究这个自然实验室，我们还可以深入了解直接观测有限的其他构造环境（例如俯冲带的近海部分）。该项目还涉及为加利福尼亚州旧金山湾区（地震危险性较高的地区）的小学生提供有关地震的教育材料。 该项目的总体目标是以前所未有的分辨率研究加利福尼亚州中部圣胡安包蒂斯塔附近圣安德烈亚斯断层瞬态地震滑动的时空尺度，最终获得对断层滑动性质的更广泛的了解。圣胡安包蒂斯塔位于圣安德烈亚斯断层蠕变段的西北边界，也是1906年旧金山Mw 7.9地震的东南终点，形成了断层蠕变到锁定的过渡。圣胡安包蒂斯塔附近密集的仪器和瞬态地震滑动的历史记录使其成为研究地震和地震滑动相互作用的绝佳天然实验室。我们将通过结合地震（一般地震活动、近重复地震）和大地测量（cGPS、InSAR、钻孔应变计、蠕变计）观测，创建圣胡安包蒂斯塔附近圣安德烈亚斯断层上自发和触发的地震滑移瞬变目录，以帮助回答以下问题：地震滑动瞬变的空间尺度、时间尺度和震级是多少？地震滑动导致中小地震的频率和机制是什么？这些地震多久会导致抗震滑移？根据瞬态地震滑移的规模，圣胡安包蒂斯塔附近的圣安德烈亚斯断层是否能够发生大地震（Mw 6）？我们将进一步研究浅层和深层地震滑移之间的关系、锁定转变中蠕变速率的时空变化，并评估近重复地震作为瞬态地震滑移代理的效用。我们还希望通过研究这个自然实验室，深入了解其他构造环境，特别是直接观测有限的俯冲带近海部分。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值进行评估，被认为值得支持以及更广泛的影响审查标准。