Faults--Offshore of San Gregorio Map Area, California

This part of SIM 3306 presents data for the faults for the geologic and geomorphic map (see sheet 10, SIM 3306) of the Offshore of San Gregorio map area, California. The vector data file is included in "Faults_OffshoreSanGregorio.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSanGregorio/data_catalog_OffshoreSanGregorio.html. The offshore San Gregorio map area lies about 15 to 25 km southwest of the San Andreas Fault, the dominant structure in the distributed transform boundary between the North American and Pacific plates. The map area straddles the right-lateral San Gregorio Fault zone, a prominent structure west of the San Andreas Fault in the broader San Andreas Fault system. The San Gregorio Fault zone occurs predominantly in the offshore and extends 400 km from Point Conception on the south to Bolinas and Point Reyes on the north (Dickinson and others, 2005), coming onland at coastal promontories such as Pescadero Point in the map area and Pillar Point, a few km north of Half Moon Bay (sheet 9). In the offshore, the San Gregorio Fault system forms a distributed shear zone about 2 to 4 km wide that includes two main diverging fault strands. The western strand (also known as the Frijoles Fault) extends offshore from Pescadero Point. The eastern strand (also known as the Coastways Fault or Seal Cove Fault), is mostly onshore in this map area. Cumulative lateral slip on the San Gregorio Fault zone is thought to range from 4 to 10 mm/yr in this region (U.S. Geological Survey, 2010). The western strand of the San Gregorio Fault zone (i.e., Frijoles Fault) forms the eastern boundary of the Pigeon Point high. Faults were primarily mapped by interpretation of seismic reflection profile data (see sheet 8, SIM 3306). The seismic reflection profiles were collected between 2007 and 2010. References Cited Dickinson, W.R., Ducea, M., Rosenberg, L.I., Greene, H.G., Graham, S.A., Clark, J.C., Weber, G.E., Kidder, S., Ernst, W.G., and Brabb, E.E., 2005, Net dextral slip, Neogene San Gregorio-Hosgri fault zone, coastal California: Geologic evidence and tectonic implications: Geological Society of America Special Paper 391, 43 p.SIM 3306的本部分提供了加利福尼亚州圣格雷戈里奥近海制图区地质与地貌图（详见SIM 3306第10幅图）的相关断层数据。矢量数据文件收录于"Faults_OffshoreSanGregorio.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreSanGregorio/data_catalog_OffshoreSanGregorio.html获取。 圣格雷戈里奥近海制图区位于圣安德烈亚斯断层（San Andreas Fault）西南约15至25公里处，该断层是北美板块与太平洋板块之间分布型转换边界的主导构造。本制图区横跨右旋圣格雷戈里奥断层带（San Gregorio Fault zone）——这是广义圣安德烈亚斯断层系统中西侧的重要构造。圣格雷戈里奥断层带主要分布于近海区域，全长400公里，南起康塞普西翁角（Point Conception），北至博利纳斯（Bolinas）与雷耶斯角（Point Reyes）（Dickinson等，2005），在制图区内的佩斯卡德罗角（Pescadero Point）以及半月湾以北数公里的皮洛角（Pillar Point）等海岸岬角处出露于陆地（第9幅图）。 在近海区域，圣格雷戈里奥断层系统形成了宽约2至4公里的分布型剪切带，包含两条主要的分叉断层支。西侧支（又称弗里霍莱斯断层（Frijoles Fault））从佩斯卡德罗角向近海延伸。东侧支（又称海岸断层（Coastways Fault）或海豹湾断层（Seal Cove Fault））在本制图区内大多位于陆上。该区域圣格雷戈里奥断层带的累计侧向滑移速率据估算为4至10毫米/年（美国地质调查局（U.S. Geological Survey），2010）。圣格雷戈里奥断层带的西侧支（即弗里霍莱斯断层）构成了佩蒂戈角高地（Pigeon Point high）的东部边界。 断层填图主要通过地震反射剖面数据解译完成（详见SIM 3306第8幅图）。这些地震反射剖面采集于2007年至2010年间。 参考文献 Dickinson, W.R.、Ducea, M.、Rosenberg, L.I.、Greene, H.G.、Graham, S.A.、Clark, J.C.、Weber, G.E.、Kidder, S.、Ernst, W.G.、Brabb, E.E.，2005，加利福尼亚沿海新近纪圣格雷戈里奥-霍斯格里断层带的总右旋滑移量：地质证据与构造意义：美国地质学会特刊391，共43页。