Folds--Offshore of San Gregorio Map Area, California

This part of SIM 3306 presents data for the folds 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 "Folds_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. 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.本数据集隶属于SIM 3306系列，包含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）的褶皱相关数据。矢量数据文件收录于"Folds_OffshoreSanGregorio.zip"压缩包，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北美板块与太平洋板块间分布型转换边界的主导构造——圣安德烈亚斯断层西南约15至25公里处。该制图区横跨右旋圣格雷戈里奥断裂带，这是广义圣安德烈亚斯断层系统中位于圣安德烈亚斯断层西侧的重要构造单元。圣格雷戈里奥断裂带主要分布于近海海域，南起康塞普西翁角，北至博利纳斯与雷耶斯角，延伸总长约400公里（Dickinson等，2005），并在制图区内的佩斯卡德罗角以及半月湾以北数公里的皮勒角等海岸岬角处出露于陆地（详见SIM 3306第9幅图）。 在近海海域，圣格雷戈里奥断裂带形成宽度约2至4公里的分布型剪切带，包含两条主要的分叉断裂支脉。西侧支脉（亦称弗里霍莱斯断层）从佩斯卡德罗角向近海延伸。东侧支脉（亦称海岸步道断层或海豹湾断层）在本制图区内主要分布于陆上。该区域圣格雷戈里奥断裂带的累计侧向滑动速率据估算为4至10毫米/年（美国地质调查局，2010）。圣格雷戈里奥断裂带西侧支脉（即弗里霍莱斯断层）构成了鸽子高地的东部边界。 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., 及 Brabb, E.E., 2005, 《加利福尼亚海岸新近纪圣格雷戈里奥-霍斯格里断裂带的右旋净滑动：地质证据与构造意义》：美国地质学会特刊391，共43页。