Faults--Offshore of Ventura, California

This part of SIM 3254 presents data for faults for the geologic and geomorphic map (see sheet 10, SIM 3254) of the Offshore of Ventura map area, California. The vector data file is included in "Faults_OffshoreVentura.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html.
The Offshore of Ventura map area is in the Ventura Basin, in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland (Fisher and others, 2009). This province has undergone significant north-south compression since the Miocene, and recent GPS data suggest north-south shortening of about 6 to 10 mm/yr (Larson and Webb, 1992; Donnellan and others, 1993). The active, north-verging Oak Ridge Fault and the south-verging Pitas Point-Ventura Fault are two of the structures on which this shortening occurs (for example, Sorlien and others, 2000; Fisher and others, 2005, 2009). High-resolution seismic-reflection profiles (sheet 8, SIM 3254) reveal that neither fault ruptures the surface; instead, the surface expression of each fault is a narrow, asymmetric fold that involves the uppermost Pleistocene and Holocene (less than 21 ka) sedimentary section. Both structures are inferred to be parts of long fault systems that extend for more than 100 km, representing important potential earthquake hazards (for example, Fisher and others, 2009). Shortening is also occurring on the Montalvo Fault and Anticline system along the southeast edge of the map area (part of the broader Oak Ridge Fault Zone; Yeats, 1998) and on the Rincon-Ventura Avenue Anticline (for example, Rockwell and others, 1988), which crosses the northwest edge of the map area.
References Cited
Donnellan, A., Hager, B.H., and King, R.W., 1993, Discrepancy between geologic and geodetic deformation rates in the Ventura basin: Nature, v. 346, p. 333?336.
Fisher, M.A., Greene, H.G., Normark, W.R., and Sliter, R.W., 2005, Neotectonics of the offshore Oak Ridge fault near Ventura, southern California: Bulletin of the Seismological Society of America, v. 95, p. 739?744.
Fisher, M.A., Sorlien, C.C., and Sliter, R.W., 2009, Potential earthquake faults offshore southern California from the eastern Santa Barbara channel to Dana Point, in Lee, H.J., and Normark, W.R., eds., 2009, Earth science in the urban ocean--The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 271-290.
Larson, K.M., and Webb, F.H., 1992, Deformation in the Santa Barbara Channel from GPS measurements 1987-1991: Geophysical News Letters, v. 19, p. 1,491-1,494.
Rockwell, T.K., Keller, E.A., and Dembroff, G.R., 1988, Quaternary rate of folding of the Ventura Avenue anticline, western Transverse Ranges, southern California: Geological Society of America Bulletin, v. 100, p. 850-858.
Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S., and Hopps, T.E, 2000, Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California: Geological Society of America Bulletin, v. 112, p. 1,080-1,090.
Yeats, R.S., 1998, North-vergent thick-skinned or south-vergent thin-skinned Oak Ridge fault--A view from the coast, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section and Coast Geological Society, Miscellaneous Publication 46, p. 143-152.

本数据集（SIM 3254）的此部分提供了加利福尼亚州文图拉近海制图区地质与地貌图（见SIM 3254第10幅）的断层相关数据。矢量数据文件存储于"Faults_OffshoreVentura.zip"压缩包中，可通过以下链接获取：http://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html。

文图拉近海制图区位于加利福尼亚大陆陆缘带以北的西横断山脉地质省（Western Transverse Ranges geologic province）南部的文图拉盆地内（Fisher等，2009）。该地质省自中新世以来经历了显著的南北向挤压作用，近期GPS监测数据显示其南北向缩短速率约为6~10毫米/年（Larson与Webb，1992；Donnellan等，1993）。活动的北逆冲橡树岭断层（Oak Ridge Fault）与南逆冲皮塔斯角-文图拉断层（Pitas Point-Ventura Fault）便是该挤压缩短作用所涉及的两类构造（如Sorlien等，2000；Fisher等，2005、2009）。高分辨率地震反射剖面（seismic-reflection profiles，SIM 3254第8幅）显示，上述两条断层均未破裂地表；其地表表现为狭窄的不对称褶皱，涉及上更新统至全新统（小于21千年）沉积层序。据推断，这两处构造均属于延伸长度超过100千米的大型断裂系统的组成部分，构成了重要的潜在地震灾害风险（如Fisher等，2009）。制图区东南边缘的蒙塔尔沃断层与背斜系统（属于更大范围的橡树岭断裂带的一部分；Yeats，1998）以及横穿制图区西北边缘的林孔-文图拉大道背斜（如Rockwell等，1988）同样存在挤压缩短作用。

参考文献
Donnellan, A., Hager, B.H. 与 King, R.W., 1993，文图拉盆地地质与大地测量变形速率间的差异：《自然》（*Nature*），第346卷，第333~336页。
Fisher, M.A., Greene, H.G., Normark, W.R. 与 Sliter, R.W., 2005，加利福尼亚南部文图拉近海橡树岭断层附近的新构造运动：《美国地震学会通报》（*Bulletin of the Seismological Society of America*），第95卷，第739~744页。
Fisher, M.A., Sorlien, C.C. 与 Sliter, R.W., 2009，从圣巴巴拉海峡东部至达纳角的南加州近海潜在地震断层：收录于Lee, H.J. 与 Normark, W.R. 主编的《城市海洋中的地球科学——南加州大陆陆缘区》，2009年，美国地质学会特刊第454号，第271~290页。
Larson, K.M. 与 Webb, F.H., 1992，1987-1991年GPS监测所得圣巴巴拉海峡区域变形：《地球物理新闻通讯》（*Geophysical News Letters*），第19卷，第1491~1494页。
Rockwell, T.K., Keller, E.A. 与 Dembroff, G.R., 1988，加利福尼亚南部西横断山脉文图拉大道背斜的第四纪褶皱速率：《美国地质学会通报》（*Geological Society of America Bulletin*），第100卷，第850~858页。
Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S. 与 Hopps, T.E., 2000，加利福尼亚州文图拉盆地陆上与近海区域橡树岭断层带褶皱与断裂晚新生代地层的图件恢复：《美国地质学会通报》（*Geological Society of America Bulletin*），第112卷，第1080~1090页。
Yeats, R.S., 1998，北逆冲厚皮构造还是南逆冲薄皮构造——橡树岭断层的海岸视角：收录于Kunitomi, D.S., Hopps, T.E. 与 Galloway, J.M. 主编的《加利福尼亚州圣巴巴拉海峡构造与石油地质》，美国石油地质学家协会太平洋分会与海岸地质学会，杂刊第46号，第143~152页。