Folds--Offshore of Ventura, California

This part of SIM 3254 presents data for folds 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 "Folds_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., 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.本部分为SIM 3254数据集，包含加利福尼亚州文图纳近海制图区地质与地貌图的褶皱数据（详见SIM 3254第10幅图）。矢量数据文件收录于"Folds_OffshoreVentura.zip"压缩包，可通过http://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html获取。 文图纳近海制图区位于文图纳盆地，地处加利福尼亚大陆边缘带以北的西横断山脉地质省（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，最新全球定位系统（GPS）数据显示其南北向构造缩短速率约为6~10 mm/yr（Larson与Webb，1992；Donnellan等，1993）。本次研究涉及的主要活动构造包括北倾奥克里奇断层（Oak Ridge Fault）与南倾皮塔斯角-文图纳断层（Pitas Point-Ventura Fault），上述南北向缩短作用即沿这两条断层发生（如Sorlien等，2000；Fisher等，2005、2009）。高分辨率地震反射剖面（SIM 3254第8幅图）显示，两条断层均未出露地表；其地表表现为窄幅不对称褶皱，涉及晚更新世最上部及全新世（小于21 ka）沉积层序。据推断，两条构造均属于延伸长度超过100 km的长距离断层系统，属于重要的潜在地震灾害隐患（如Fisher等，2009）。制图区东南部边缘的蒙塔尔沃断层与背斜系统（属于更广泛的奥克里奇断层带的一部分；Yeats，1998），以及横穿制图区西北部的林孔-文图纳大道背斜（如Rockwell等，1988）同样存在构造缩短作用。 参考文献 Donnellan, A., Hager, B.H. 与 King, R.W., 1993，文图纳盆地地质与大地测量变形速率的差异：《自然》（*Nature*），第346卷，第333~336页。 Fisher, M.A., Greene, H.G., Normark, W.R. 与 Sliter, R.W., 2005，加利福尼亚州南部文图纳近海奥克里奇断层的新构造活动：《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到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，《城市海洋中的地球科学——加利福尼亚南部大陆边缘带》：美国地质学会特刊454，第271-290页。 Larson, K.M. 与 Webb, F.H., 1992，1987-1991年圣巴巴拉海峡的GPS测量变形：《地球物理快讯》（*Geophysical News Letters*），第19卷，第1491~1494页。 Rockwell, T.K., Keller, E.A. 与 Dembroff, G.R., 1988，加利福尼亚州南部西横断山脉文图纳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，加利福尼亚州文图纳盆地陆上及近海奥克里奇断层带褶皱与断层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，北倾厚皮构造与南倾薄皮构造的奥克里奇断层——来自海岸的视角，收录于Kunitomi, D.S., Hopps, T.E. 与 Galloway, J.M. 主编，《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46，第143~152页。