A model for Neogene crustal rotations, transtension, and transpression in southern California

Luyendyk, Bruce P.

doi:10.1130/0016-7606(1991)103<1528:amfncr>2.3.co;2

Cited by 191 publications

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“…these results consistent with the tectonic model of Luyendyk [1991], who proposed continuous counterclockwise rotation of the oblique segment since Miocene. Unlike the velocity field, which is not so sensitive to the grid design [Li, 1994], the strain rate field is sensitive to the size of the grid area as well as the grid design (see equation (1)).…”

Section: Strain Rate Deficitssupporting

confidence: 81%

Contemporary kinematics of the western United States determined from earthquake moment tensors, very long baseline interferometry, and GPS observations

Shen-Tu¹,

Holt²,

Haines³

1998

J. Geophys. Res.

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Abstract. Using moment tensors from earthquakes between 1850 and 1995, we determine the horizontal velocity gradient tensor field associated with the seismic deformation in the western U.S. plate boundary zone. The velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5 ø of the NUVEL-1A PacificNorth American plate motion direction. The magnitude of the earthquake-related velocity is 62% of the NUVEL-1A total Pacific-North American plate motion. If earthquake occurrence is a random, Poisson-like process, then the large formal errors associated with the model velocity estimates are an indication that the 144-year interval is too short to define the longterm seismic moment release rate to within an uncertainty less than the deficit between the observed seismic moment release rate and the total long-term moment release rate associated with both the seismic and aseismic deformation. To spatially resolve the deficit of the earthquake moment release in the last 144 years, we have also estimated the total long-term horizontal velocity gradient tensor field using seismic strain rate tensors and recent geodetic velocities, both with and without the NUVEL-1A Pacific-North American rigid plate motion constraint. We find a systematic difference between the Southern California Earthquake Center (SCEC) geodetic velocity map and NUVEL-1A North American reference frames with a pole at (38.8øN, 124.2øW, 0.33 ø m.y.-1). This difference is significant at the 99% confidence level and indicates that 4-7 mm/yr of NE-SW convergence is absorbed in offshore areas of southern California if both the SCEC velocity map and NUVEL-1A correctly describe the relative motion between the Pacific and North America plates. Deficit strain rates calculated from comparison of observed seismic strain rates over the last 144 years with long-term model strain rate tensors are largest in areas east of San Francisco Bay, in the Transverse Ranges, and along the southern San Andreas fault and San Jacinto fault. The deficit in each 100 by 50 km grid area within these regions is equivalent to an accumulation of strain in the last 144 years that would be released by an Mw > 7 earthquake. Elsewhere the accumulated strain in the last 144 years is small, except in northern Mojave Desert, along the Garlock fault, and in the region southwest of the southern San Andreas-San Jacinto fault zone. Within each 100 by 50 km grid area in these regions the accumulated strain is equivalent to that released by an Mw -6.5-7.0 earthquake. Introduction Deformation in the western

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Section: Strain Rate Deficitssupporting

confidence: 81%

Contemporary kinematics of the western United States determined from earthquake moment tensors, very long baseline interferometry, and GPS observations

Shen-Tu¹,

Holt²,

Haines³

1998

J. Geophys. Res.

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“…An eclogitic root forms a gravitationally metastable layer within the lithosphere that, in the Sierra Nevada, delaminated only after extension began in the adjacent Basin and Range province. Adjacent extension could also be the trigger for delamination of the lithosphere beneath the Peninsular Range, but extension began earlier at 15 -20 Ma in the Borderlands region [Luyendyk, 1991;Bohannon and Geist, 1998] before switching eastward to the Gulf of California, so delamination may have begun sooner and progressed further. Perhaps upwelling of the asthenosphere replacing the delaminated lithosphere has ceased at shallow levels, or never reached as shallow as the Sierra Nevada detachment, because we do not see the pronounced low-velocity anomalies that are present beneath the eastern edge of the Sierra Nevada at 50 to 70 km.…”

Section: Peninsular Range Drip and Mojave Anomalymentioning

confidence: 99%

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Yang¹,

Forsyth²

2006

J. Geophys. Res.

142

192

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[1] We use Rayleigh waves to invert for shear velocities in the upper mantle beneath southern California. A one-dimensional shear velocity model reveals a pronounced lowvelocity zone (LVZ) from 90 to 210 km. The pattern of velocity anomalies indicates that there is active small-scale convection in the asthenosphere and that the dominant form of convection is three-dimensional (3-D) lithospheric drips and asthenospheric upwellings, rather than 2-D sheets or slabs. Several of the features that we observe have been previously detected by body wave tomography: these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern Sierra Nevada and Walker Lane region; sinking lithosphere beneath the southern Central Valley; upwelling beneath the Salton Trough; and downwelling beneath the Transverse Ranges. Our new observations provide better constraints on the lateral and vertical extent of these anomalies. In addition, we detect two previously undetected features: a high-velocity anomaly beneath the northern Peninsular Range and a low-velocity anomaly beneath the northeastern Mojave block. We also estimate the azimuthal anisotropy from Rayleigh wave data. The strength is $1.7% at periods shorter than 100 s and decreases to below 1% at longer periods. The fast direction is nearly E-W. The anisotropic layer is more than 300 km thick. The E-W fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms: pure shear in the lithosphere due to N-S tectonic shortening and simple shear in sublithosphere mantle due to mantle flow.

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“…• of ongoing clockwise rotation of the Transverse Ranges (Atwater 1989;Luyendyk 1991;Crouch & Suppe 1993). The formation of the left step 'big bend' in the San Andreas fault occurred 12-4 Myr ago (Crowell 1968;Atwater 1970;Stock & Hodges 1989;Wright 1991) and is the most likely source of oblique convergence in southern California (Crowell 1968).…”

Section: Introductionmentioning

confidence: 99%

Anisotropy from SKS splitting across the Pacific-North America plate boundary offshore southern California

Ramsay¹,

Kohler²,

Davis³

et al. 2016

Geophys. J. Int.

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S U M M A R YSKS arrivals from ocean bottom seismometer (OBS) data from an offshore southern California deployment are analysed for shear wave splitting. The project involved 34 OBSs deployed for 12 months in a region extending up to 500 km west of the coastline into the oceanic Pacific plate. The measurement process consisted of removing the effects of anisotropy using a range of values for splitting fast directions and delay times to minimize energy along the transverse seismometer axis. Computed splitting parameters are unexpectedly similar to onland parameters, exhibiting WSW-ENE fast polarization directions and delays between 0.8 and 1.8 s, even for oceanic plate sites. This is the first SKS splitting study to extend across the entire boundary between the North America and Pacific plates, into the oceanic part of the Pacific plate. The splitting results show that the fast direction of anisotropy on the Pacific plate does not align with absolute plate motion (APM), and they extend the trend of anisotropy in southern California an additional 500 km west, well onto the oceanic Pacific plate. We model the finite strain and anisotropy within the asthenosphere associated with density-buoyancy driven mantle flow and the effects of APM. In the absence of plate motion effects, such buoyancy driven mantle flow would be NE-directed beneath the Pacific plate observations. The best-fit patterns of mantle flow are inferred from the tomography-based models that show primary influences from foundering higher-density zones associated with the history of subduction beneath North America. The new offshore SKS measurements, when combined with measurements onshore within the plate boundary zone, indicate that dramatic lateral variations in density-driven upper-mantle flow are required from offshore California into the plate boundary zone in California and western Basin and Range.

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A model for Neogene crustal rotations, transtension, and transpression in southern California

Cited by 191 publications

References 0 publications

Contemporary kinematics of the western United States determined from earthquake moment tensors, very long baseline interferometry, and GPS observations

Contemporary kinematics of the western United States determined from earthquake moment tensors, very long baseline interferometry, and GPS observations

Rayleigh wave phase velocities, small‐scale convection, and azimuthal anisotropy beneath southern California

Anisotropy from SKS splitting across the Pacific-North America plate boundary offshore southern California

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