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SIM 3306数据集的此部分，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）相关的褶皱数据。矢量数据文件收录于"Folds_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25千米处；圣安德烈亚斯断层是北美板块与太平洋板块之间分布型转换边界的主控构造。该制图区横跨右旋圣格雷戈里奥断裂带，该断裂带是广义圣安德烈亚斯断层系中圣安德烈亚斯断层西侧的标志性构造。圣格雷戈里奥断裂带主体分布于近海区域，整体延伸长度达400千米，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），并在制图区内的佩斯卡德罗角（Pescadero Point）以及半月湾以北数千米的柱石角（Pillar Point）等海岸岬角处出露陆地（详见第9幅图）。

在近海区域，圣格雷戈里奥断裂系形成了宽约2至4千米的分布型剪切带，包含两条主要的分支断裂。西侧分支（又称弗里霍莱斯断层（Frijoles Fault））从佩斯卡德罗角向近海延伸。东侧分支（又称海岸断层（Coastways Fault）或海豹湾断层（Seal Cove Fault））在本制图区内主体位于陆域。美国地质调查局（U.S. Geological Survey, 2010）认为，该区域内圣格雷戈里奥断裂带的累计侧向滑移速率介于4至10毫米/年之间。圣格雷戈里奥断裂带的西侧分支（即弗里霍莱斯断层）构成了鸽子点海隆（Pigeon Point High）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年，加利福尼亚沿海新近纪圣格雷戈里奥-霍斯格里断裂带的净右旋滑移：地质证据与构造意义：美国地质学会特刊391，共43页。