Uplift of the Western Transverse Ranges and Ventura Area of Southern California: A Four‐Technique Geodetic Study Combining GPS, InSAR, Leveling, and Tide Gauges

Abstract

We estimate the rate of vertical land motion (VLM) in the region around the Western Transverse Ranges (WTR), Ventura, and Big Bend of the San Andreas Fault (SAF) of southern California using data from four geodetic techniques: GPS, interferometric synthetic aperture radar (InSAR), leveling, and tide gauges. We use a new analysis technique called GPS Imaging to combine the techniques and leverage the synergy between (1) high geographic resolution of InSAR, (2) precision, stability, and geocentric reference frame of GPS, (3) decades long observation of VLM with respect to the sea surface from tide gauges, and (4) relative VLM along dense leveling lines. The uncertainty in the overall rate field is ~1 mm/yr, though some individual techniques have uncertainties as small as 0.2 mm/yr. The most rapid signals are attributable to subsidence in aquifers and groundwater changes. Uplift of the WTR is geographically continuous, adjacent to the SAF and appears related to active crustal contraction across Pacific/North America plate boundary fault system. Uplift of the WTR and San Gabriel Mountains is ~2 mm/yr and is asymmetrically focused west of the SAF, consistent with interseismic strain accumulation across thrust faults in the Ventura area and Santa Barbara channel that accommodate contraction against the near vertical SAF.

Structural modeling of the Western Transverse Ranges: An imbricated thrust ramp architecture

“…The low dip that we infer for the underlying thrust ramp in our model predicts that a geodetic uplift signal should be observable to the north of the Santa Ynez range, contrary to that from the steeper dips inferred for other models (Sorlien and Nicholson, 2015;Nicholson et al, 2017). Our model is consistent with the geodetic uplift signal north of the Santa Ynez range (Hammond et al, 2018), which indicates that the deep thrust related to the shortening at the brittleductile transition zone is in the same area as we predict.…”

Tracking California’s sinking coast from space: Implications for relative sea-level rise

“…S4 and S5). Again, disagreement with other longterm vertical rates derived for this region (34,40,42,43) reenforces that this uplift is indeed an aquifer recharge signal. Tectonics also likely contribute to this region's deformation pattern.…”

“…We also see subsidence in the Ventura basin, likely related to groundwater extraction, which agrees with results from Hammond et al . ( 34 ).…”

Submerged paleoshoreline mapping using high-resolution Chirp sub-bottom data, Northern Channel Islands platform, California, USA

“…The NCI are considered part of the Transverse Range province, which experiences increased uplift due to transpressional deformation along the Big Bend of the San Andreas Fault. Uplift rates for this province vary, but have been measured as high as 6–7 mm/yr onshore at Ventura, California (Rockwell et al, 2016), and 2 mm/yr in the Western Transverse Range and San Gabriel Mountains (Hammond et al, 2018). The lower uplift rates of the NCI identified here align better with regional uplift rates for San Diego County and other offshore islands within the California Continental Borderlands (Kern and Rockwell, 1992; Haaker et al, 2016), which has implications for the tectonic evolution of the southern California region.…”

“…The lower uplift rate estimates for the islands are more consistent with regional uplift rates from southern California of 0.13–0.27 m/ka (Ku and Kern, 1974; Kern and Rockwell, 1992; Grant et al, 1999; Mueller et al, 2009; Haaker et al, 2016) than with uplift rates within the onshore Transverse Range province (Muhs et al, 2014; Rockwell et al, 2016). Recent measurements of vertical motion on SCI and SRI using GPS stations north of the SCIF and SRIF show a slight (< 0.5 mm/yr) subsidence (Hammond et al, 2018).…”