The San Andreas fault (California, USA) is near vertical at shallow (< 10 km) depth. Geophysical surveys along the San Andreas fault reveal that, at depths of 10–20 km, it dips ~50–70° to the southwest near the Western Transverse Ranges and dips northeast in the San Gorgonio region. We investigate the possible origin of along-strike geometric variations of the fault using a three-dimensional thermomechanical model. For two blocks separated by transpressional faults, our model shows that viscous lower crustal material moves from the high-viscosity block into the low-viscosity block. Fault plane-normal flow in the viscous lower crust rotates the fault plane due to the simple shear flow at the brittle-ductile transition depth. This occurs irrespective of initial fault dip direction. Rheological variations used to model the lower crust of Southern California are verified by independent observations. Block extrusion due to lower crustal viscosity variation facilitates the formation of the Garlock Fault and sustains the geometric complexity of the fault.
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Research Article|
June 21, 2022
Crustal transpressional fault geometry influenced by viscous lower crustal flow
Haibin Yang;
Haibin Yang
1
Research School of Earth Sciences, Australian National University, Canberra ACT 2600, Australia2
School of Earth Sciences, University of Melbourne, VIC 3010, Australia
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Louis N. Moresi;
Louis N. Moresi
1
Research School of Earth Sciences, Australian National University, Canberra ACT 2600, Australia
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Mark Quigley;
Mark Quigley
2
School of Earth Sciences, University of Melbourne, VIC 3010, Australia3
Seismology Research Centre, Richmond, VIC 3121, Australia
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Metin Kahraman;
Metin Kahraman
4
Eurasia Institute of Earth Sciences, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
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Doğan Kalafat
Doğan Kalafat
5
Kandilli Observatory and Earthquake Research Institute, Boğaziçi University, 34684 Çengelköy, Istanbul, Turkey
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Geology (2022)
Article history
received:
21 Jan 2022
rev-recd:
28 Apr 2022
accepted:
01 May 2022
first online:
21 Jun 2022
Citation
Haibin Yang, Louis N. Moresi, Mark Quigley, Metin Kahraman, Doğan Kalafat; Crustal transpressional fault geometry influenced by viscous lower crustal flow. Geology 2022; doi: https://doi.org/10.1130/G50061.1
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