Bridging earthquakes and mountain building in the Santa Cruz Mountains, CA

Abstract

Relative crustal motions along active faults generate earthquakes, and repeated earthquake cycles build mountain ranges over millions of years. However, the long-term summation of elastic, earthquake-related deformation cannot produce the deformation recorded within the rock record. Here, we provide an explanation for this discrepancy by showing that increases in strain facilitated by plastic deformation of Earth’s crust during the earthquake cycle, in conjunction with isostatic deflection and erosion, transform relative fault motions that produce individual earthquakes to geologic deformations. We focus our study on the data-rich Santa Cruz Mountains, CA, USA and compare predicted and observed quantities for rock uplift, apatite (U-Th)/He thermochronology, topographic relief, 10 Be-based erosion rates, and interseismic surface velocities. This approach reconciles these disparate records of mountain-building processes, allowing us to explicitly bridge decadal measures of deformation with that produced by millions of years of plate motion.

Space Geodetic Evidence of Basement‐Involved Thick‐Skinned Orogeny and Fault Frictional Heterogeneity of the Papuan Fold Belt, Papua New Guinea

“…However, due to the mechanical coupling between elastic coseismic slip and off‐fault deformation (i.e., fold growth), it is difficult to distinguish quantitively the folding‐related contribution during large earthquake, which should be considered in the fault kinematics inversion and deserves further study to illustrate more realistic earthquake deformation processes in fold and thrust belts. Numerical modeling of short‐term and long‐term deformation with elastoplastic rheologies, using the finite element method, is one approach to tackle this kind of coupled problem (e.g., Baden et al., 2022).…”

Flexural Response to Erosional Unloading of Continental Margins: An Example From the Bering Sea, USA

“…Flexural isostasy incorporates the elastic properties of the lithosphere, which vary laterally and vertically, necessitating a spatially averaged value. Using the approach of Baden et al (2022), we calculate the three-dimensional flexural response to a volume load by solving the two-dimensional, thin-plate flexure equation:…”

“…Using the approach of Baden et al. (2022), we calculate the three‐dimensional flexural response to a volume load by solving the two‐dimensional, thin‐plate flexure equation: $$$D\,{\nabla }^{4}w-{\rho }_{m}gw=\left({\rho }_{c}-{\rho }_{w}\right)g{\increment}H$$$ where w is the deflection of the ocean bottom, $${\rho }_{m}$$, $${\rho }_{c}$$, and $${\rho }_{w}$$ are the densities of the mantle, crust, and water, respectively, g is gravitational acceleration, $${\increment}H$$ is the change in elevation of the seafloor due to erosion or deposition, and D is the flexural rigidity, defined as: $$$D=\frac{E{T}_{e}^{3}}{12\left(1-{\nu }^{2}\right)}.$$$ Where E is the Young's modulus of the crust, ν is Poisson's Ratio, and T e is the effective elastic thickness of the crust. This equation is solved using a Fourier Transform approach (Hodgetts et al., 1998).…”

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

“…This configuration is used to construct Greens functions relating plate motion to vertical displacement rates ($$\boldsymbol{U}$$ [L/t]) at all channel points. By explicitly prescribing the surfaces of the FTB faults for modeling topographic growth and crustal deformation along the plate boundary, we provide an alternative strategy to others that account for strain‐hardening, plastic yielding, and isostatic and flexural compensation, in the absence of relief‐bounding, subsidiary faults (e.g., Baden et al., 2022). Next, the publicly available, 10‐m‐resolution National Elevation Data set Digital Elevation Model (DEM) was used to route flow over the topography by filling internal sinks before calculating watershed area ($$A$$ [L 2 ]), which is in turn used to identify all measured channel elevation points ($${z}_{m}$$ [L]) in the SA, defined as having catchment areas >0.1 km 2 (see Supporting Information ; Figure S3; Data Set S2 in Supporting Information ).…”

“…These reverse faults have apparently formed due to an ∼11° left-bend in the San Andreas Fault, which converts shearing into contraction (Anderson, 1990(Anderson, , 1994Aydin & Page, 1984) and leads to the construction of the >1.2-km-high Southern Santa Cruz Mountains or Sierra Azul (hereafter referred to as SA) (Figure 1). While the Pacific Block has been advected through the restraining bend, the North American (Bay) Block has remained relatively immobile (Baden et al, 2022). The most recent recorded significant earthquake that may have occurred along these structures, of M = 6.5, was in 1865 A.D. (Ellsworth, 1990;Tuttle & Sykes, 1992;Yu & Segall, 1996).…”