Finite element model predictions of static deformation from dislocation sources in a subduction zone: Sensitivities to homogeneous, isotropic, Poisson‐solid, and half‐space assumptions

Abstract

[1] Dislocation models can simulate static deformation caused by slip along a fault. These models usually take the form of a dislocation embedded in a homogeneous, isotropic, Poisson-solid half-space (HIPSHS). However, the widely accepted HIPSHS assumptions poorly approximate subduction zone systems of converging oceanic and continental crust. This study uses three-dimensional finite element models (FEMs) that allow for any combination (including none) of the HIPSHS assumptions to compute synthetic Green's functions for displacement. Using the1995 M w = 8.0 Jalisco-Colima, Mexico, subduction zone earthquake and associated measurements from a nearby GPS array as an example, FEM-generated synthetic Green's functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface. Loading a forward HIPSHS model with dislocation distributions, estimated from FEMs that sequentially relax the HIPSHS assumptions, yields the sensitivity of predicted displacements to each of the HIPSHS assumptions. For the subduction zone models tested and the specific field situation considered, sensitivities to the individual Poisson-solid, isotropy, and homogeneity assumptions can be substantially greater than GPS measurement uncertainties. Forward modeling quantifies stress coupling between the M w = 8.0 earthquake and a nearby M w = 6.3 earthquake that occurred 63 days later. Coulomb stress changes predicted from static HIPSHS models cannot account for the 63-day lag time between events. Alternatively, an FEM that includes a poroelastic oceanic crust, which allows for postseismic pore fluid pressure recovery, can account for the lag time. The pore fluid pressure recovery rate puts an upper limit of 10 À17 m 2 on the bulk permeability of the oceanic crust.INDEX TERMS: 1242 Geodesy and Gravity: Seismic deformations (7205); 3230 Mathematical Geophysics: Numerical solutions; 3260 Mathematical Geophysics: Inverse theory; 7215 Seismology: Earthquake parameters; 7223 Seismology: Seismic hazard assessment and prediction; KEYWORDS: finite element models, pororelastic theory, static deformation, stress coupling, material properties, tectonic hazards Citation: Masterlark, T., Finite element model predictions of static deformation from dislocation sources in a subduction zone: Sensitivities to homogeneous, isotropic, Poisson-solid, and half-space assumptions,

Pyroclastic Flow Deposits and InSAR: Analysis of Long-Term Subsidence at Augustine Volcano, Alaska

“…Numerical modeling has proven highly effective in estimating deformation, particularly when geometric data, such as deposit thickness from repeated DEMs, are unavailable [20]. Modeling, however, may require significantly simplifying assumptions, and be valid only for individual field situations [66]. The results from our study, such as deposit thickness and deformation, can provide an important method to numerical modeling and help increase the reliability and precision of geophysical estimates.…”

Impact of megathrust geometry on inversion of coseismic slip from geodetic data: Application to the 1960 Chile earthquake

“…The matrix G integrates geometry, material properties and meshing of the FEM model, constructed following the technique of Masterlark [2003]. In doing so, a forward model runs as many times as the number of nodes on the fault.…”

“…It has been well recognized that inversion procedures may affect the slip distribution solution [Beresnev, 2003]. Incorrect assumptions about fault geometries [Lee et al, 2006], crustal structure [Savage, 1987;Masterlark, 2003], and smoothing constraints [Du et al, 1992] may significantly affect the predicted slip distribution. Moreover, the spatial heterogeneity of the model resolution may lead to artifacts in poorly resolved areas of the fault plane [Page et al, 2009].…”

Contributions of poroelastic rebound and a weak volcanic arc to the postseismic deformation of the 2011 Tohoku earthquake

“…Migration of fluids thus causes the pore fluid pressure to evolve towards an equilibrium condition in which the earthquake-induced fluid flow has completed, commonly referred to as 'drained' condition. This time-dependent process (e.g., Jónsson et al, 2003;Masterlark, 2003) is controlled by the variable viscosities of fluids, the rock properties, and the complex permeability structure of the lithosphere. A common way to predict the deformation resulting from the completed poroelastic rebound is to consider only the difference in elastic coseismic deformation between the undrained condition immediately after the earthquake and the fully relaxed equilibrium condition long after the earthquake (e.g., Masterlark, 2003;Jónsson et al, 2003).…”

“…This time-dependent process (e.g., Jónsson et al, 2003;Masterlark, 2003) is controlled by the variable viscosities of fluids, the rock properties, and the complex permeability structure of the lithosphere. A common way to predict the deformation resulting from the completed poroelastic rebound is to consider only the difference in elastic coseismic deformation between the undrained condition immediately after the earthquake and the fully relaxed equilibrium condition long after the earthquake (e.g., Masterlark, 2003;Jónsson et al, 2003). This is accomplished by differencing coseismic deformation models in which portions of the lithosphere where earthquake-induced fluid flow is believed to occur are modeled with undrained and equilibrium values of Poisson's ratio.…”