Developments in Understanding the Tectonic Evolution of the California Continental Borderland

Legg, Mark R.

doi:10.2110/pec.91.09.0291

Cited by 40 publications

(50 citation statements)

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“…Our model also shows low-velocity anomalies associated with the offshore basins, such as in the Santa Monica Basin, the San Pedro Basin, the Catalina Basin, the Gulf of Catalina, and the San Diego Trough. The intermediate-to high-velocity anomaly on the Santa Catalina Island might be associated with the uplifted Catalina Schist [e.g., Woodford, 1924;Bailey, 1941;Platt, 1975;Legg, 1991]. In the Mojave Desert, our model shows lower velocities in the Antelope Valley than CVM-S4 and CVM-H11.9.…”

Section: Model Descriptionmentioning

confidence: 74%

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

et al. 2014

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We have successfully applied full-3-D tomography (F3DT) based on a combination of the scattering-integral method (SI-F3DT) and the adjoint-wavefield method (AW-F3DT) to iteratively improve a 3-D starting model, the Southern California Earthquake Center (SCEC) Community Velocity Model version 4.0 (CVM-S4). In F3DT, the sensitivity (Fréchet) kernels are computed using numerical solutions of the 3-D elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process. More than half-a-million misfit measurements made on about 38,000 earthquake seismograms and 12,000 ambient-noise correlagrams have been assimilated into our inversion. After 26 F3DT iterations, synthetic seismograms computed using our latest model, CVM-S4.26, show substantially better fit to observed seismograms at frequencies below 0.2 Hz than those computed using our 3-D starting model CVM-S4 and the other SCEC CVM, CVM-H11.9, which was improved through 16 iterations of AW-F3DT. CVM-S4.26 has revealed strong crustal heterogeneities throughout Southern California, some of which are completely missing in CVM-S4 and CVM-H11.9 but exist in models obtained from previous crustal-scale 2-D active-source refraction tomography models. At shallow depths, our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike-slip and dip-slip faults. At middle to lower crustal depths, structural features in our model may provide new insights into regional tectonics. When combined with physics-based seismic hazard analysis tools, we expect our model to provide more accurate estimates of seismic hazards in Southern California.

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Section: Model Descriptionmentioning

confidence: 74%

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

et al. 2014

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“…Removal of an additional 32 km of oblique extension across San Diego Trough juxtaposes Thirtymile Bank against Coronado Bank (Fig. 2b), and positions Catalina and Navy craters as possible sources for volcanic and volcaniclastic rocks in the middle Miocene Rosarito Beach basin (Legg 1991 (Luyendyk et al 1998).…”

Section: Regi O N a L G E O L O G Y T E C T O N I C S A N D E V E N mentioning

confidence: 99%

Large enigmatic crater structures offshore southern California

Legg

Nicholson

Goldfinger

et al. 2004

Geophysical Journal International

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S U M M A R YDigital mosaics of swath and conventional bathymetry data reveal large, distinct near-circular crater structures in the Inner Continental Borderland offshore southern California. Two have maximum crater diameters that exceed 30 km and a third has a crater diameter of approximately 12 km. All three features exhibit the morphology of large complex craters (raised outer rim, ring moat and central uplift) yet their exact origin remains a mystery. Preliminary analyses of available seismic, gravity and magnetic data over these structures reveal both similarities and distinct differences in geometry, structure and geophysical signature to known impact sites. All three crater structures, however, occur within the Catalina terrane, a highly extended volcanic and metamorphic province floored by Catalina schist basement. A likely alternative origin may thus involve explosive volcanism, caldera collapse and resurgent magmatism, and/or possibly plutonism and schist remobilization associated with the Catalina terrane. No single model for crater formation, whether impact, caldera or pluton, fully accounts for all of the present observations regarding the morphology, internal structure and known geology of these nearcircular features. Timing of crater formation post-dates the initial rifting and rotation of the western Transverse Ranges, and appears to predate major right slip along the San Clemente and San Diego Trough fault systems-or approximately 18 to 16 Ma. Regardless of their origin, these complex craters represent some of the largest structures of their kind in western North America and provide a unique opportunity to better understand the development of unusual crater structures in a submarine environment.

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“…The California Continental Borderland is a vigorous and complex component of the Pacific-North America plate boundary that has experienced subduction, rifting and transform faulting in the relatively short interval between the Oligocene (36 Ma) and the present. Over time, geometrical irregularities of the plate boundary have forced large crustal blocks to rotate, producing both contraction and extension within postulated microplates caught between the Pacific and North American plates proper (Legg 1991; Legg & Kennedy Although the California Continental Borderland is an active part of a plate boundary, the complexity of its geodynamic evolution and the difficulties involved in collecting submarine geological data have limited the resolution of its tectonic traits 1991). The Borderland contains many faults and compressive geological structures that accommodate both compressional and strike-slip components of Pacific-North America plate motion.…”

Section: Introductionmentioning

confidence: 99%

Progressive growth of San Clemente Island, California, by blind thrust faulting: implications for fault slip partitioning in the California Continental Borderland

Ward

Valensise

1996

Geophysical Journal International

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We find that the genesis of San Clemente Island and its surrounding submarine platform is consistent with progressive slip on two, southeast‐striking, southwest‐dipping, blind thrust fault segments. Since their inception 2 to 5 Ma, 3 km of compression normal to the N150°E fault strike has been accommodated with 1700 m of domal uplift of the San Clemente Anticlinorium. The existence of an extensive suite of Pleistocene marine terraces provides evidence that slip and uplift are continuing today. Based on direct terrace fossil age determinations and correlations of terrace heights with global sea‐level curves, we estimate that San Clemente Island is currently uplifting at between 0.2 and 0.5 mm yr−1. This translates into 0.6–1.5 mm yr−1 of thrusting on the causative blind thrusts beneath the island. Unlike the situation at nearby Palos Verdes, where a simple twist in a regional strike‐slip fault accommodated both fault‐parallel and fault‐normal motions, the shallow dips of the thrusts suggest that, if regional strike‐slip motion on the San Clemente Fault exists, it must be partitioned onto through‐going surfaces distinct from the thrusts. Current GPS data are sparse and equivocal, but they indicate that 1–4 mm yr−1 of compression and 4–7 mm yr−1 of strike slip are absorbed in the California Continental Borderland. With the Palos Verdes Fault taking some 3 mm yr−1 from the strike‐slip budget, 1–4 mm yr−1 of motion could be present on a through‐going San Clemente Fault. When translated into an annual moment release rate using Kostrov's formula, GPS strains predict that between 2.5 and 4.9 times 1017 N m yr−1 of earthquake potential is available offshore from San Diego to the Santa Barbara Channel. Distribution of this moment budget among various earthquake magnitudes is arguable, but we predict that M > 6 quakes in the Borderland could recur between 30 and 80 years, and M > 7 quakes might be found every 310 to 580 years.

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Developments in Understanding the Tectonic Evolution of the California Continental Borderland

Cited by 40 publications

References 0 publications

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

Large enigmatic crater structures offshore southern California

Progressive growth of San Clemente Island, California, by blind thrust faulting: implications for fault slip partitioning in the California Continental Borderland

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