# US 2012/0239298 A1 · Geological Stress Inversion Using Fault Displacement and Slip Tendency

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- Number: US 2012/0239298 A1
- Document ID: US20120239298A1
- Status: Published application
- Kind: A1
- Application number: 13/047,704
- Filed: 2011-03-14
- Published: 2012-09-20
- Earliest claimed: 2011-03-14
- Assignees: Southwest Research Institute
- Inventors: Alan P. Morris; David A. Ferrill; John M. McFarland
- Web page: https://patentgrep.com/patent/US20120239298A1

## CPC

- G01V 20/00: Geomodelling in general
- G01V 1/01: Measuring or predicting earthquakes
- G01V 2210/642: Faults
- G01V 2210/663: Modeling production-induced effects
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

A computer-implemented method of determining the stress state associated with a geological fault is described. The source data comprises measured fault displacement values, or proxy displacement values, associated with the fault. An error function calculates error as a function of normalized fault displacement and normalized slip tendency. Candidate stress states are used to determine slip tendency values, which are used in the error function to calculate an error value. This value is minimized to determine the “best” candidate stress state.

## Claims

### Claim 1

A computer-implemented method of determining the stress state associated with a geological fault, comprising:
storing a dataset representing fault displacement values, or proxy displacement values, associated with the fault;
storing an error function that calculates error as a function of normalized fault displacement and normalized slip tendency;
selecting principal stress values for a stress state;
calculating the slip tendency for that stress state for each measurement in the data set;
calculating an error value for the data set, using the error function, the slip tendency, and the displacement or the proxy displacement values;
repeating the selecting and calculating steps for a number of stress states; and
determining the stress state that minimizes the error value.

### Claim 2 (depends on 1)

The method of claim 1, wherein the proxy displacement values are fault area values.

### Claim 3 (depends on 1)

The method of claim 1, wherein the proxy displacement values are seismic focal values.

### Claim 4 (depends on 1)

The method of claim 1, wherein the proxy values are earthquake magnitude values.

### Claim 5 (depends on 1)

The method of claim 1, wherein the error function is conditionally calculated depending on whether the displacement value or proxy displacement value is greater than the slip tendency.

### Claim 6 (depends on 5)

The method of claim 5, wherein the error function is further conditionally calculated depending on whether the displacement value or proxy displacement value is zero.

### Claim 7 (depends on 1)

The method of claim 1, wherein the error function is conditionally calculated such that the error measure is large if the displacement is large relative to slip tendency, but small if the displacement is small relative to slip tendency.

### Claim 8 (depends on 1)

The method of claim 1, wherein the step of calculating an error value is performed by means of a sum of squares function.

### Claim 9 (depends on 1)

The method of claim 1, wherein the step of determining the stress state that minimizes the error value is performed using a nonlinear regression method.