Mountain Rivers Reveal the Earthquake Hazard of Geologic Faults in Silicon Valley

Abstract

The 1989, Mw = 6.9 Loma Prieta earthquake resulted in tens of lives lost and cost California almost 3% of its gross domestic product. Despite widespread damage, the earthquake did not clearly rupture the surface, challenging the identification and characterization of these hidden hazards. Here, we show that they can be illuminated by inverting fluvial topography for slip‐and moment accrual‐rates—fundamental components in earthquake hazard assessments—along relief‐generating geologic faults. We applied this technique to thrust faults bounding the mountains along the western side of Silicon Valley in the San Francisco Bay Area, and discovered that these structures may be capable of generating a Mw = 6.9 earthquake every 250–300 years based on moment accrual rates. This method may be deployed broadly to evaluate seismic hazard in developing regions with limited geological and geophysical information.

Climate aridity delays morphological response of Andean river valleys to tectonic uplift

“…With these boundary conditions, tribemx uses Green's functions (Meade, 2007) to calculate, firstly, the slip vector, with its corresponding strike and dip slip components, at the centroid of each triangular element (e.g., Aron et al, 2022). Secondly, a displacement vector and its horizontal and vertical components on a regular 10 km grid on the Earth's surface.…”

“…We used the 8400 m grid as the final output and average the results of the seismic and interseismic model runs. The Green's functions are used to calculate vertical displacement as a percentage of the total convergence rate (e.g., Aron et al, 2022). Using two control points on the Earth's surface we scaled these dimensionless rock uplift values, x: Xnorm = x -rmin/ rmax -rmin (tmax -tmin)+tmin where rmin and rmax are understood to be the minimum and maximum modelled values of x, and tmin and tmax are minimum and maximum values of xnorm.…”

“…Without independent constraint on the spatial distribution of fault motion across the Argentinian cordillera, relatively high rock uplift rates would have been overlooked in this region and would not have been interpreted by classical river profile inversion techniques (e.g. Goren et al, 2014;Aron et al, 2022).…”

“…Many field studies have focused on modelling this observation with stream power geomorphic incision rules in tectonically active landscapes (e.g. Goren et al, 2014;Kirby and Whipple, 2001;Leonard and Whipple, 2021;Racano et al, 2021;Aron et al, 2022). This detachment-limited style model implicitly assumes river profiles evolve to maintain a transport capacity equal to its sediment flux, such that the bed resistance to detachment by the flow controls the incision rate.…”

“…In this way, channel steepness (the steepness of a channel normalised by its drainage area) is considered an indicator of the vertical incision rate and dependent on the tectonic and climatic boundary conditions acting on the landscape (Kirby and Whipple, 2012;Hilley et al, 2019). Where channel steepness can be normalised by a uniform value of profile concavity, spatial patterns in steepness are being increasingly used to map spatial variability in tectonic uplift or bedrock erodibility (Kirby and Whipple, 2001;Goren et al, 2014;Leonard and Whipple, 2021;Racano et al, 2021;Aron et al, 2022), assuming erosion has kept pace with uplift and is time-invariant (Perron and Royden, 2013). This assumption that erosion has kept pace with uplift, however, is limiting in many settings and is particularly restrictive when exploring the impact of climate on river channel networks.…”