Oiler

Note: This project is still in rapid development and not sufficiently tested by those other than me.

Oiler is a program for modeling tectonic block motions on a sphere, in particular for solving for best-fit, kinematically-consistent fault slip rates given both geologic fault slip rate estimates and GNSS-type geodetic velocities. The primary motivation is in estimating a complete and internally- consistent set of fault slip rates for all faults in a region for seismic hazard assessment, though of course more traditional earth-science research may find use here as well. Because of this motivation, Oiler is fault-first in that it directly uses fault data (traces and other geometry, slip rates, kinematics) produced by geologic investigation and required to build fault-source models for seismic hazard analysis.

Oiler aims to be fast and (sort of) interactive, so that a scientist can progressively build a fault and block network in a GIS program, quantifying fault slip rate estimates given data and network details, and adjusting weights, slip rates, fault connectivity and block geometry iteratively based on rapid modeling results from Oiler. Once the workflow and IO are streamlined, more details on this will be available.

Foundationally, Oiler solves for the poles and rates of rotation between adjacent blocks separated by faults, constrained by relative velocities between blocks, through the relation

V = Omega x RP

where V represents the velocity of a point P relative to some block, Omega is the rotation vector (pole and rate) describing relative block motion, and RP is the Cartesian representation of the location P. If three or more blocks are present in a model, velocity closures are imposed so that all velocities in the solution are internally consistent.

Oiler treats both fault slip rate estimates and GNSS data as velocities V, differing only in two aspects: Fault slip rates may only constrain motions between adjacent blocks separated by the fault (though any number of faults may separate two blocks), while GNSS velocities may constrain the motions between any block and the geodetic reference frame (which may or may not be an actual block in the model). GNSS data are also subject to earthquake-cycle velocity perturbations (i.e., the effects of interseismic fault locking) that geologic fault velocities are not.

The use of both velocity data types allows relative velocities between blocks to be estimated regardless of whether any or all blocks contain GNSS stations, which allows the modeler to incorporate many more faults and honor fault network geometry, particularly in remote and poorly-studied areas where GNSS data are sparse to nonexistent.

Oiler draws heavily from the previous research into plate/block theory and to a lesser extent, previous implementations. The mathematical formulations of Meade and Loveless (2009), Chase (1972), and Cox and Hart (1986) were extremely helpful, and I am very grateful to those authors for their careful and thorough explanations. Additionally, implementation details of certain parts of the code here, particularly fault locking or earthquake cycle effects, were modeled after the Blocks code by Meade and Loveless. I double thank Meade and Loveless for making their code public and with a permissive license.

Installation

To install Oiler, first install the Julia language.

Then, in a Julia terminal, hit the ] button to get into the package manager command line. Then type add https://github.com/cossatot/Oiler/src/Oiler.jl