Locking depths estimated from geodesy and seismology along the San Andreas Fault System: Implications for seismic moment release

Abstract

[1] The depth of the seismogenic zone is a critical parameter for earthquake hazard models. Independent observations from seismology and geodesy can provide insight into the depths of faulting, but these depths do not always agree. Here we inspect variations in fault depths of 12 segments of the southern San Andreas Fault System derived from over 1000 GPS velocities and 66,000 relocated earthquake hypocenters. Geodetically determined locking depths range from 6 to 22 km, while seismogenic thicknesses are largely limited to depths of 11-20 km. These seismogenic depths best match the geodetic locking depths when estimated at the 95% cutoff depth in seismicity, and most fault segment depths agree to within 2 km. However, the Imperial, Coyote Creek, and Borrego segments have significant discrepancies. In these cases the geodetically inferred locking depths are much shallower than the seismogenic depths. We also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates (1.5-1.8 × 10 13 Nm/yr/km) along the Mojave and Carrizo segments and low rates (∼0.2 × 10 13 Nm/yr/km) along several San Jacinto segments. The largest difference in seismic moment between models is calculated for the Imperial segment, where the moment rate from seismic depths is a factor of ∼2.5 larger than that from geodetic depths. Such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated.Citation: Smith-Konter, B. R., D. T. Sandwell, and P. Shearer (2011), Locking depths estimated from geodesy and seismology along the San Andreas Fault System: Implications for seismic moment release,

Estimation of present-day inter-seismic deformation in Kopili fault zone of north-east India using GPS measurements

“…The best-fit elastic loading curve estimates a right lateral slip of 2.62 § 0.79 mm/yr and a shallow locking depth (3 § 2 km), which is consistent with the slip reported by Vernant et al (2014). To better constrain the locking depth, we require dense GPS sites within one half of the actual locking depth (Smith-Konter et al 2011). We have only two pairs of sites adjacent to strike of the Kopili fault on opposite sides which are not sufficient to resolve the locking depth to sufficient accuracy.…”

The vertical fingerprint of earthquake cycle loading in southern California

“…Note that earthquake cycle effects 44,45 , as well as a smooth transition from locked to unlocked fault 46 , are known to complicate estimations of true locking depth. Apparent locking depths range between 0 and 22 km, and are primarily consistent with seismicity depths 47,48 and provide a root-mean-square residual velocity model misfit of less than 2 mm yr −1 (ref. 11).…”

Block‐like plate movements in eastern Anatolia observed by InSAR

“…Our estimation appears to be robust and not driven by any particular data set, as similar shallow locking depth values are obtained when using any of the three different InSAR data sets alone in the estimation. A deeper locking depth is found along the EAF further to the west ( 15 km) [Walters, 2013], indicating that there are significant locking depth variations along the fault, as have been identified along some other faults [Smith-Konter et al, 2011], including along the NAF [Kaneko et al, 2013].…”