Shallow seismic imaging of folds above the Puente Hills blind‐thrust fault, Los Angeles, California

Pratt, Thomas L.; Shaw, John H.; Dolan, James F.; Christofferson, Shari A.; Williams, Robert A.; Odum, Jack K.; Plesch, Andreas

doi:10.1029/2001gl014313

Cited by 34 publications

(33 citation statements)

References 15 publications

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“…Bedding parallel flexural slip formed by both coseismic and postseismic motion as documented in the La Laja area where 30 cm of this movement was produced along a period of weeks after the main earthquake [ Castellanos , 1944; Groeber , 1944]. Surface deformation is apparently dominated by folding [ Kadinsky‐Cade et al , 1985; Krugh , 2003; Meigs et al , 2007] similar to other well‐documented blind thrust earthquakes such as those in the Los Angeles Basin [e.g., Yeats and Huftile , 1995; Shaw and Suppe , 1996; Pratt et al , 2002]. …”

Section: Discussionmentioning

confidence: 95%

Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas‐Precordillera interaction

et al. 2007

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We document a new model of crustal structure of the Andean front in Argentina where numerous historic earthquakes destroyed the cities of Mendoza in 1861 (Ms = ∼7) and San Juan in 1944 (Mw = 7.0). The Cerro Salinas anticline is formed above the west directed Cerro Salinas thrust. An east facing monocline with an amplitude of about 2 km folds the Cerro Salinas thrust and overlying Neogene succession. This monocline is formed above a blind crustal thrust in the basement. Its dip of 14° west is inferred from fold geometry. This thick‐skinned east directed blind thrust and the thin‐skinned west directed Cerro Salinas thrust define a tectonic wedge; the wedge tip occurs at a depth of 5.4 km. Growth of the monocline after ∼8.5 Ma is revealed on multichannel seismic (MSC) profile 31017 (Repsol‐YPF). Rates of Cerro Salinas thrust displacement are of the order of 1 mm/yr, whereas vertical uplift of ∼0.45 mm/yr results from the combined displacement on the Cerro Salinas thrust and growth of east facing monocline. The lateral extent of the east directed crustal blind ramp corresponds with the along‐strike extent of the Eastern Precordillera. When combined with the low displacement rate, a long earthquake recurrence interval is implied. Smaller magnitude earthquakes, however, indicate that segments of the blind thrust ramps ruptured in historic events. If all the segments of the blind thrust ruptured together the fault area is ∼7000 km2 and could produce a Mw ∼ 7.7 earthquake. The crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region.

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Section: Discussionmentioning

confidence: 95%

Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas‐Precordillera interaction

et al. 2007

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“…2). A similar seismogenic structural wedge underlies Wheeler Ridge in the southern San Joaquin Valley (Medwedeff, 1992) and the Coyote Hills segment of the Puente Hills blind-thrust fault in the Los Angeles basin (Pratt et al, 2002). According to faultbend fold theory (Suppe, 1983), the total shortening on the wedge thrust is equal to the 6-km width of the kink fold between the active axial surface A1 and the inactive axial surface A2 (Figs.…”

Section: Revised Structural Model For the Seattle Fault Zonementioning

confidence: 99%

Earthquakes generated from bedding plane-parallel reverse faults above an active wedge thrust, Seattle fault zone

Kelsey

Sherrod

Nelson

et al. 2008

Geological Society of America Bulletin

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A key question in earthquake hazard analysis is whether individual faults within fault zones represent independent seismic sources. For the Seattle fault zone, an upper plate structure within the Cascadia convergent margin, evaluating seismic hazard requires understanding how north-side-up, bedding-plane reverse faults, which generate late Holocene fault scarps, interact with the north-vergent master-ramp thrust and overlying backthrust of the fault zone. A regional uplift at A.D. 900-930 involved an earthquake that nucleated at depth and included slip on both the master-ramp thrust and the backthrust. This earthquake also included slip on some of the <6-km-deep north-side-up, bedding-plane reverse faults. At locales where the north-side-up reverse faults intersect the Puget Sound coast, an earthquake a few centuries earlier than the A.D. 900-930 regional uplift only uplifted areas within hundreds of meters north of the reverse faults. We infer that the bedding-plane reverse faults are seismogenic because shore platforms near the reverse faults have been abruptly uplifted during earthquakes when other shorelines in the Seattle fault zone were unaffected. Faults of the Seattle fault zone therefore can both produce regional uplift earthquakes, with or without surface displacement on the reverse faults, and produce earthquakes that rupture the bedding-plane reverse faults causing fault scarps and uplift localized to hundreds of meters north of these faults. This latter type of earthquake has occurred at least twice and perhaps three times in the late Holocene, and all these earthquakes preceded the regional coseismic uplift of A.D. 900-930. To account for the paleoseismic observations, we propose that the Seattle fault zone is a wedge thrust, with the leading edge being a fault-bend, wedge thrust fold. The active axial surface of the wedge thrust fold is pinned at the tip of the wedge, and a steeply north-dipping sequence of Tertiary sediment forms the south limb of the wedge thrust fold. Some of these steeply north-dipping, bedding-plane surfaces are seismogenic reverse faults that produce scarps. Earthquakes on the wedge thrust produce the regional coseismic uplift events, and earthquakes within the faultbend fold cause the local uplift earthquakes. Thus, bedding-plane faults can rupture during earthquakes when the wedge thrust does not rupture but instead continues to accumulate seismic energy.

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“…1). We began this project fully aware that seismic surveying of active blind faults and folds can be a daunting task (Pratt et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

First seismic imaging results of tectonically complex structures at shallow depths beneath the northwest Canterbury Plains, New Zealand

Dorn

Carpentier

Kaiser

et al. 2010

Journal of Applied Geophysics

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Shallow seismic imaging of folds above the Puente Hills blind‐thrust fault, Los Angeles, California

Cited by 34 publications

References 15 publications

Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas‐Precordillera interaction

Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas‐Precordillera interaction

Earthquakes generated from bedding plane-parallel reverse faults above an active wedge thrust, Seattle fault zone

First seismic imaging results of tectonically complex structures at shallow depths beneath the northwest Canterbury Plains, New Zealand

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