Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific‐North America plate boundary through the San Bernardino Mountains, California

Abstract

Campaign GPS data collected from 2002 to 2014 result in 41 new site velocities from the San Bernardino Mountains and vicinity. We combined these velocities with 93 continuous GPS velocities and 216 published velocities to obtain a velocity profile across the Pacific-North America plate boundary through the San Bernardino Mountains. We modeled the plate boundary-parallel, horizontal deformation with 5-14 parallel and one obliquely oriented screw dislocations within an elastic half-space. Our rate for the San Bernardino strand of the San Andreas Fault (6.5 ± 3.6 mm/yr) is consistent with recently published latest Quaternary rates at the 95% confidence level and is slower than our rate for the San Jacinto Fault (14.1 ± 2.9 mm/yr). Our modeled rate for all faults of the Eastern California Shear Zone (ECSZ) combined (15.7 ± 2.9 mm/yr) is faster than the summed latest Quaternary rates for these faults, even when an estimate of permanent, off-fault deformation is included. The rate discrepancy is concentrated on faults near the 1992 Landers and 1999 Hector Mine earthquakes; the geodetic and geologic rates agree within uncertainties for other faults within the ECSZ. Coupled with the observation that postearthquake deformation is faster than the pre-1992 deformation, this suggests that the ECSZ geodetic-geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the timescale of an earthquake cycle, rather than a redistribution of plate boundary slip at a timescale of multiple earthquake cycles or longer.

Short-term variations in slip rate and size of prehistoric earthquakes during the past 2000 years on the northern San Jacinto fault zone, a major plate-boundary structure in southern California

“…Recent geodetic studies seem to favor the San Jacinto-dominated scenario when looking specifically at the northern San Jacinto fault and San Bernardino segment of the San Andreas fault (e.g., Meade and Hager, 2005;Spinler et al, 2010;Loveless and Meade, 2011;McGill et al, 2014). These studies, which use elastic models of geodetic data, consistently suggest slower slip rates on the San Bernardino segment of the San Andreas fault than along the San Andreas in Coachella Valley, most likely due to faults of the Eastern California shear zone accommodating some of the displacement north of Coachella Valley.…”

Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California

“…The San Jacinto section diverges from the San Bernardino section and reaches a slip rate of ~15 mm/yr at the Quincy site [see Onderdonk et al , , and references therein]. Geodetic rates for the San Jacinto Fault (12–21 mm/yr) are comparable to inferred geologic rates [ Fay and Humphreys , ; Spinler et al , ; McGill et al , ]. The San Bernardino strand at the SGP may terminate, be overridden by thrust faults, or merge with the SGP fault zone, complicating our understanding of fault zone continuity [e.g., Yule and Sieh , ].…”

“…The San Bernardino section has a well‐documented slip‐rate decrease from ~25 mm/yr at Cajon Pass to ~8 mm/yr at Burro Flats [see McGill et al , , and references therein]. Geodetic strain rates across this section also appear to decrease to <10 mm/yr due to the southward transfer of slip onto the San Jacinto section [ Meade and Hager , ; Becker et al , ; Spinler et al , ; Loveless and Meade , ; McGill et al , ]. The San Jacinto section diverges from the San Bernardino section and reaches a slip rate of ~15 mm/yr at the Quincy site [see Onderdonk et al , , and references therein].…”

How fault evolution changes strain partitioning and fault slip rates in Southern California: Results from geodynamic modeling

“…The present‐day slip rates on many of these faults in Southern California have been well constrained by space geodetic measurements; exceptions are the blind faults in western Transverse Ranges, the diffuse faults across the Mojave Desert, and the offshore faults where GPS measurements are sparse [ Becker et al ., ; McCaffrey , ; Meade and Hager , ; Spinler et al ., ; Loveless and Meade , ; Johnson , ; McGill et al ., ; Zeng and Shen , ]. However, the slip rates constrained from geodetic data differ from geological estimates on many faults [ Oskin et al ., ; Bird , ; Chuang and Johnson , ; Loveless and Meade , ; Lindsey and Fialko , ; Tong et al ., ; Zeng and Shen , ; McGill et al ., ; Evans et al ., ]. The discrepancies may arise from the uncertainty of geodetic inversion methods [ Johnson , ], or geological measurements [ Bird , ; Zechar and Kurt , ], or both; but some of the discrepancies are likely due to the different timescales of the geodetic and geological data, the latter reflect longer timescales during which the fault slip rates may have changed by the initiation of new faults in the plate boundary zone [ Morton and Matti , ; Bennett et al ., ].…”

“…The fault evolution in Southern California implies continuous changes of strain partitioning across the plate boundary zone and slip rates on all faults in the system. The present‐day slip rates on many of these faults in Southern California have been well constrained by space geodetic measurements; exceptions are the blind faults in western Transverse Ranges, the diffuse faults across the Mojave Desert, and the offshore faults where GPS measurements are sparse [ Becker et al ., ; McCaffrey , ; Meade and Hager , ; Spinler et al ., ; Loveless and Meade , ; Johnson , ; McGill et al ., ; Zeng and Shen , ]. However, the slip rates constrained from geodetic data differ from geological estimates on many faults [ Oskin et al ., ; Bird , ; Chuang and Johnson , ; Loveless and Meade , ; Lindsey and Fialko , ; Tong et al ., ; Zeng and Shen , ; McGill et al ., ; Evans et al ., ].…”