Lenwood-Lockhart fault zone, Lenwood section (Class A) No. 111b
Last Review Date: 2000-09-20
Compiled in cooperation with the California Geological Survey
citation for this record: Bryant, W.A., compiler, 2000, Fault number 111b, Lenwood-Lockhart fault zone, Lenwood section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 05/11/2024 02:15 PM.
| Synopsis |
General:
Major Holocene active dextral strike-slip fault zone located in the Central Mojave Desert. Fault zone is divided into two sections for this compilation; the Lockhart and Lenwood sections. Detailed reconnaissance-level geologic and geomorphic mapping of the fault zone includes Dibblee (1958 #6627; 1960 #6628; 1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1968 #6631; 1970 #6640), Page and Moyle (1960 #6637), Morton and others (1980 #6636), Manson (1986 #6642), Bryant (1987 #6626), and Padgett (1994 #6643). Traces of the Lenwood fault at Soggy Lake had up to 5 cm of triggered dextral displacement associated with the 1992 Mw 7.3 Landers earthquake (Hart and others, 1993 #3356). Minor historic fault creep has been reported on the northern Lenwood fault in the town of Lenwood (D. Morton and C. Gray, personal communication in Manson, 1986 #6642), although Manson (1986 #6642) was not able to verify evidence of systematic fault creep. Padgett (1994 #6643) excavated two fault normal trenches across traces of the Lenwood fault at Soggy Lake and exposed evidence of 3 paleoearthquakes in the past 8.2 ka. Padgett's (1994 #6643) event chronology identified large surface-faulting events 1.8±0.2 ka and 8.2±0.2 ka, suggesting a recurrence interval of about 6,000 yrs. An additional event at 6.4±0.2 ka was interpreted by Padgett to be a small displacement event, probably similar to the triggered slip observed along the Lenwood fault after the 1992 Landers earthquake. Padgett (1994 #6643) concluded that the Lenwood fault ruptures in 3-m displacement events and estimated a Holocene slip rate of about 0.5 mm/yr. Petersen and Wesnousky (1994 #6024) estimated a preferred long term slip rate of 0.8 mm/yr (0.05–1.5 mm/yr), based on 1.5–3.0 km dextral offset of the Kane Springs fault and initiation of slip between 2 Ma and 20 Ma. Sections: This fault has 2 sections. There is insufficient data to designate seismogenic segments. Petersen and others (1996 #4860)(1996) combined the Lockhart, Lenwood, and Old Woman Springs [117] faults as a single seismic source and termed this the Lenwood-Lockhart fault zone. This nomenclature is adopted in this compilation, but the Old Woman Springs [117] is considered separately. The section boundary between the Lockhart fault to the north and the Lenwood fault to the south is located near the town of Lenwood. Southeast of Lenwood, the Lenwood-Lockhart fault zone strikes about N. 30° W. and is delineated by generally well defined geomorphic evidence of Holocene dextral displacement. Northwest of Lenwood the fault zone strikes N. 55–60° W. and, though locally there is geomorphic evidence of Holocene dextral slip, the fault zone generally lacks geomorphic evidence of Holocene displacement (Manson, 1986 #6642; Bryant, 1987 #6626). |
| Name comments |
General: Lenwood fault was first mapped (partly) by Vaughn (1922 #5801) and first named and completely mapped by Dibblee (1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1970 #6640). Lockhart fault was first mapped and named by Dibblee (1958 #6627; 1960 #6628; 1968 #6631). Petersen and others (1996 #4860) modeled a Mw 7.3 earthquake along the Lenwood, Lockhart, and Old Woman Springs [117] faults and termed this fault zone the Lenwood-Lockhart fault zone. Lenwood-Lockhart fault zone in this compilation includes the North Lockhart fault (Dibblee, 1968 #6631) and an unnamed fault on west side of Harper Lake (Bryant, 1987 #6626). Section: Lenwood section proposed in this compilation, based on fault source modeling by Petersen and others (1996 #4860). Section extends from the town of Lenwood southeast to the northern front of the San Bernardino Mountains. Fault ID: Refers to numbers 381 (Lenwood fault), 365 (Lockhart fault), and 366 (unnamed fault west side Harper Lake) of Jennings, (1994 #2878). |
| County(s) and State(s) |
SAN BERNARDINO COUNTY, CALIFORNIA |
| Physiographic province(s) |
BASIN AND RANGE |
| Reliability of location |
Good Compiled at 1:62,500 scale. Comments: Locations based on digital revisions to Jennings (1994 #2878) using original mapping by Dibblee (1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1970 #6640) at 1:62,500; geomorphic mapping by Morton and others (1980 #6636) and Manson (1986 #6642) at 1:24,000.
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| Geologic setting |
Holocene active dextral strike slip fault zone located in the central Mojave Desert. The northwest-striking Lenwood-Lockhart fault zone is part of a series of subparallel dextral strike-slip faults in the central Mojave Desert and is part of the eastern California shear zone (Dokka and Travis, 1990 #3188). The Lenwood-Lockhart fault zone extends from about 17 km southeast of Fremont Valley (Garlock fault zone [69]) southeast across the Mojave River, along the northeastern side of Stoddard Valley, through the central Ord Mountains, and terminates about 1 km north of the northern San Bernardino Mountains where it probably complexly merges with the North Frontal thrust system [109]. Cumulative dextral displacement along the Lenwood fault is about 1.5–3 km, based on displacement of Miocene detachment (Dokka and Travis, 1990 #3188). Garfunkel (1974 #6633) estimated about 15–20 km dextral offset along the Lenwood fault, based on modeling.
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| Length (km) | This section is 74 km of a total fault length of 142 km. |
| Average strike | N31°W |
| Sense of movement |
Right lateral
Comments: Dibblee (1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1970 #6640). Dokka and Travis (1990 #3188) documented 1.5 to 3 km of dextral displacement of Miocene detachment terrane.
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| Dip Direction |
V
Comments: Dibblee (1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1970 #6640)
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| Paleoseismology studies |
Site 111-1 by Padgett (1994 #6643) involved the excavation of two fault normal trenches across the trace of the Lenwood fault at the Soggy Lake playa in order to constrain the timing and size of past large surface faulting earthquakes. The size of prior surface rupture events was estimated based on surveying of dextrally offset stream channels. Eleven detrital charcoal samples were dated using AMS 14C methods and dendrochronologically corrected.
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| Geomorphic expression |
Lenwood fault is delineated by moderately to well defined geomorphic features indicative of Holocene dextral slip such as dextrally offset drainages, linear drainages, sidehill benches, shutter ridges, closed depressions, linear scarps and vegetation contrasts on late Pleistocene and Holocene alluvium, and offset alluvial fans (Bull, 1978 #6613; Morton and others, 1980 #6636; Manson, 1986 #6642; Padgett, 1994 #6643).
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| Age of faulted surficial deposits | Fault offsets Mesozoic crystalline basement rocks, Miocene sedimentary rocks, Pleistocene and Holocene alluvium (Dibblee, 1960 #6638; 1964 #1249; 1964 #6639; 1967 #6614; 1970 #6640). Padgett (1994 #6643) identified offset Holocene and late Holocene deposits (1.8 ka to 8.2 ka) along the Lenwood fault at the Soggy Lake paleoseismic site (111-1). |
| Historic earthquake | |
| Most recent prehistoric deformation |
latest Quaternary (<15 ka)
Comments: Padgett (1994 #6643) identified the most recent paleoevent as occurring 1.8±0.2 ka. The penultimate event occurred 6.4±0.2 ka, but probably was a triggered slip event similar to the slip observed on the Lenwood fault following the 1992 Mw7.3 Landers earthquake (Padgett, 1994 #6643).
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| Recurrence interval |
about 6 k.y.
Comments: Padgett (1994 #6643) identified 3 paleoevents at the Soggy Lake paleoseismic site (111-1) in the past 8.2 k.y., not including the 5 cm dextral triggered slip from the 1992 Landers earthquake (Hart and others, 1993 #3356). The event chronology interpreted by Padgett (1994 #6643) is: Historic 5 cm triggered slip associated with 1992 Mw 7.3 Landers earthquake Event 1 1.8±0.2 ka Event 2 6.4±0.2 ka Event 3 8.2±0.2 ka Events 1 and 3 were large surface rupturing earthquakes and Padgett (1994 #6643) interpreted Event 2 to be a triggered slip event similar to the 1992 Landers event. An approximately 6,000 yr recurrence interval for large surface-rupturing earthquakes is indicated |
| Slip-rate category |
Between 0.2 and 1.0 mm/yr
Comments: Padgett (1994 #6643) estimated Holocene slip rate of about 0.5 mm/yr. This is based on the recurrence interval of about 6 k.y. and estimated slip per event of 3 m. The slip per event is based on surveys of 7 dextrally offset stream channels. These displacement values clustered at 3 m, with additional poorly constrained slip values clustering at 6 m, 9 m, and 15 m. Petersen and Wesnousky (1994 #6024) estimated a preferred long-term slip rate of 0.8 mm/yr (0.05 mm/yr to 1.5 mm/yr), based on 1.5 km to 3.0 km dextral offset of Kane Springs fault and initiation of slip between 2 Ma and 20 Ma. Slip rate assigned by Petersen and others (1996 #4860) for probabilistic seismic hazard assessment for the State of California was 0.6 mm/yr (with minimum and maximum assigned slip rates of 0.2 mm/yr and 1.0 mm/yr, respectively. |
| Date and Compiler(s) |
2000
William A. Bryant, California Geological Survey |
| References |
#6626 Bryant, W.A., 1987, Recently active traces of the Blackwater, Harper, Lockhart and related faults near Barstow, San Bernardino County: California Division of Mines and Geology Fault Evaluation Report FER-189, microfiche copy in California Division of Mines and Geology Open-File Report 90-14, 17 p., scale 1:24,000. #6613 Bull, W.B., 1978, Tectonic geomorphology of the Mojave Desert: Technical report to U.S. Geological Survey Earthquake Hazard Reduction Program, Reston, Virginia, under Contract 14-08-001-G-394, 176 p. #6627 Dibblee, T.W., Jr., 1958, Geologic map of the Boron quadrangle, Kern and San Bernardino Counties, California: U.S. Geological Survey Mineral Investigations Field Studies Map MF 204, scale 1:62,500. #6628 Dibblee, T.W., Jr., 1960, Geologic map of the Hawes quadrangle, San Bernardino County, California: U.S. Geological Survey Mineral Investigations Field Studies Map MF 226, scale 1:62,500. #6638 Dibblee, T.W., Jr., 1960, Geologic map of the Barstow quadrangle, San Bernardino County, California: U.S. Geological Survey Mineral Investigations Field Studies Map MF 233, scale 1:62,500. #1249 Dibblee, T.W., Jr., 1964, Geologic map of the Ord Mountains quadrangle San Bernardino County, California: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-427, 6 p. pamphlet, 1 sheet, scale 1:62,500. #6639 Dibblee, T.W., Jr., 1964, Geologic map of the Rodman Mountains quadrangle, San Bernardino County, California: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-430, scale 1:62,500. #6614 Dibblee, T.W., Jr., 1967, Geologic map of the Old Woman Springs quadrangle, San Bernardino County, California: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-518, scale 1:62,500. #6631 Dibblee, T.W., Jr., 1968, Geology of the Fremont Peak and Opal Mountains quadrangles, California: California Division of Mines and Geology Bulletin 188, scale 1:62,500. #6640 Dibblee, T.W., Jr., 1970, Geologic map of the Daggett quadrangle, San Bernardino County, California: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-592, scale 1:62,500. #3188 Dokka, R.K., and Travis, C.J., 1990, Late Cenozoic strike-slip faulting in the Mojave Desert, California: Tectonics, v. 9, p. 311-340. #6633 Garfunkel, Z., 1974, Model for the late Cenozoic tectonic history of the Mojave Desert, California and for its relation to adjacent areas: Geological Society of America Bulletin, v. 85, p. 1931-1944. #3356 Hart, E.A., Bryant, W.A., and Treiman, J.A., 1993, Surface faulting associated with the June 1992 Landers earthquake, California: California Geology, v. 46, p. 10-16. #2878 Jennings, C.W., 1994, Fault activity map of California and adjacent areas, with locations of recent volcanic eruptions: California Division of Mines and Geology Geologic Data Map 6, 92 p., 2 pls., scale 1:750,000. #6642 Manson, M., 1986, Lenwood, Old Woman Springs fault, and Silver Reef fault, San Bernardino County: California Division of Mines and Geology Fault Evaluation Report FER-177, microfiche copy in California Division of Mines and Geology Open-File Report 90-14), 13 p., scale 1:24,000. #6636 Morton, D.M., Miller, F.K., and Smith, C.C., 1980, Photoreconnaissance maps showing young-looking fault features in the southern Mojave Desert, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1051, 7sheets, scale 1:24,000 and 1:62,500. #6643 Padgett, D.C., 1994, Paleoseismology of the Lenwood fault, Mojave Desert, San Bernardino County, California: Los Angeles, CA, California State University, unpublished M.S. thesis, 90 p., 3 appendices. #6637 Page, R.W., and Moyle, W.R., Jr., 1960, Data on water wells in the eastern part of the middle Mojave Valley area, San Bernardino County, California: California Department of Water Resources Bulletin 91-3, 223 p., 2 pls. #6024 Petersen, M.D., and Wesnousky, S.G., 1994, Fault slip rates and earthquake histories for active faults in southern California: Bulletin of the Seismological Society of America, v. 84, no. 5, p. 1,608-1,649. #4860 Petersen, M.D., Bryant, W.A., Cramer, C.H., Cao, T., Reichle, M.S., Frankel, A.D., Lienkaemper, J.J., McCrory, P.A., and Schwartz, D.P., 1996, Probabilistic seismic hazard assessment for the State of California: California Department of Conservation, Division of Mines and Geology Open-File Report 96-08 (also U.S. Geological Open-File Report 96-706), 33 p. #5801 Vaughn, R.E., 1922, Geology of San Bernardino Mountains north of San Gorgonio Pass: Berkeley, California, University of California Publications in Geological Sciences, v. 13, no. 9, p. 319-411. |