SCEC Community Stress Model (CSM)

The SCEC Community Stress Model (CSM) is a group of models of stress and stressing rate within the southern California crust and lithosphere, compiled by the CSM Working Group of the Southern California Earthquake Center (SCEC).  

“Stress” models are models of the 3-D symmetric stress tensor (6 components), describing the forces present within a continuous volume.  “Stressing rate” models are models of how the 3-D stress tensor changes over time, for example due to stress accumulating along a tectonic plate boundary.

The CSM is one of several SCEC Community Models, but differs in that it does not attempt to provide a single consensus model of stress or stressing rate.  Instead, the intention is to compile a set of models of stress and stressing rate.  The current version of the CSM includes 11 distinct models: 6 of stress, and 5 of stressing rate.  The model techniques, assumptions, and input datasets vary, so no two models provide the exact same result.  Table 1, in the README file, provides a summary of some of the basic attributes of each model contribution.  In some cases, the contributed models have been published in a peer reviewed journal.  In other cases, the methods or datasets were previously published in a peer reviewed journal, but the exact contributed model is not published. 

For the six stress models, the orientation of the stress tensor is mostly derived from the inversion of earthquake focal mechanisms.  Three of the models are based solely on earthquake focal mechanisms, and thus do not provide information on stress magnitude.  One model provides an estimate of the deviatoric stress required to support existing topography.  Two models provide an estimate of the full absolute stress tensor, based on forward physics-based modeling of the tectonic loading of the southern California fault system.  Note that even when sampled “on” a major fault surface, these model values should be regarded as estimates of stress in the adjacent continuum rather than estimates from “within” fault gouge zones.

The five stressing rate models are mostly based on kinematic or mechanical models constrained by geodetic data.  Some are based on estimates of velocity field or strain rate that are then translated into stressing rate.  Others involve forward physics-based modeling of tectonic loading of the fault system, but focus on deriving stressing rate rather than the absolute stress tensor.

Each of the models was contributed by an author or group of authors, the earliest in 2012, the most recent in 2017.  Values in the crust (≤ 25 km depth) are reported for a uniform grid of latitude and longitude points, covering southern California at a resolution of ~2 km (0.0180º latitude, 0.0217º longitude), for a total of 72,325 unique points.  Values in the deeper lithosphere (≥ 50 km) are reported for a uniform grid with a resolution of ~5 km (0.0450º latitude, 0.0543º longitude), for a total of 11,493 unique points.  Depths are reported every 2 km from 1 km to 25 km depth, and then every 25 km to 100 km depth, for a total of 16 unique depths.  Points that lie outside the defined volume for a particular model, given its assumptions and available data, are omitted from that model’s file.
 
The model contributions include the 6-component cartesian stress tensor (in East, North, Up, tension positive) at each grid point, and then several values calculated from the tensor components that describe different aspects of the orientation or magnitude of the 3-D tensor.  For visualization of these models, see the CSM web viewer on the SCEC CSM homepage, https://www.scec.org/research/csm.

From 2012 - 2016, the CSM working group undertook a series of comparison exercises to understand where the models agree and disagree about the orientation and magnitude of stress and stressing rate.  Broadly, stress models tend to agree in orientation but disagree about magnitude.  Stressing rate models tend to agree along major fault segments, but disagree in secondary fault or off-fault areas.  For details see the SCEC CSM homepage,
https://www.scec.org/research/csm.