Who is working on this?
Andreas Plesch, Kristian Bergen,
John Shaw

In collaboration with:
SCEC, USGS, CGS

Fig. 1: Map view of the CFM-R in which regions for which an additional, alternative fault models is available are highlighted with colored outlines of the fault patches.

Abstract

CFM-R is a simplified, rectilinear version of CFM, the SCEC Community Fault Model. It tracks the releases of CFM in parallel.

Method

Each fault was subdivided into 5km or longer patches. The downdip sides of each patch are parallel to each other and perpendicular to the strike line (the fault trace in map view). The lower corner points are at the depth of the seismogenic thickness surface used in CFM. Coordinates in all files are given in the UTM zone 11, NAD 27 projection.

Processing and file format

For each patch a triangulated gocad tsurf description exists. This description includes markers for the vertices of the corner points. In a first processing step the vertex locations of all corner points for each patch along with the name of the patch were extracted from the gocad description. The vertices were then sorted according to depth. The lower and upper corner point pair were also reordered according to their easting. This sorting results in most cases in the downdip sides of each polygon being defined by the 1st and 3rd, and 2nd and 4th point. At this point both the upper and lower pair has variable depths for each corner. An additional calculation averages these depths for each pair but does not modify the easting and northing. Finally the dip for each side is calculated given the corner point sorting.

Each resulting data file has all data for each polygon on one line, in this order:
name dipA dipB depthA depthB topA topB xdA xdB xtA xtB ydA ydB ytA ytB

where
name: gocad name of fault
dipA: dip at side A
dipB: dip at side B
depthA: depth at side A
depthB: depth at side B
topA: top elevation at side A
topB: top elevation at side B
xdA: X coordinate (x) at deep (d) corner of side A (A)
xdB: X coordinate (x) at deep (d) corner of side B (B)
xtA: X coordinate (x) at top (t) corner of side A (A)
xtB: X coordinate (x) at top (t) corner of side B (B)
ydA: X coordinate (y) at deep (d) corner of side A (A)
ydB: X coordinate (y) at deep (d) corner of side B (B)
ytA: X coordinate (y) at top (t) corner of side A (A)
ytB: X coordinate (y) at top (t) corner of side B (B)

Alternative representations

In order facilitate use of alternative fault representation which are included in CFM, 4 regions were defined which each have 2 alternative fault models:

1. Los Angeles basin (LA)
2. Ventura basin (VN)
3. Santa Barbara channel (SB)
4. Death Valley (DV)

The fault model file for each region plugs seamlessly into the main fault model file. One can mix and match all combinations of alternative models for a total of 16 different combinations.

Fig. 2 : First alternative fault model of the Santa Barbara
           channel region.

Downloads

For simplicity all data files are archived in one compressed tar file:

cfm2.5-r_alt_regions.tar.gz

This archive contains:

cfm2.5-r_dv_alt1.4cad
cfm2.5-r_dv_alt1.4cvd
cfm2.5-r_dv_alt2.4cad
cfm2.5-r_dv_alt2.4cvd
cfm2.5-r_la_alt1.cad
cfm2.5-r_la_alt1.cvd
cfm2.5-r_la_alt2.cad
cfm2.5-r_la_alt2.cvd
cfm2.5-r_main.4cad
cfm2.5-r_main.4cvd
cfm2.5-r_sb_alt1.4cad
cfm2.5-r_sb_alt1.4cvd
cfm2.5-r_sb_alt2.4cad
cfm2.5-r_sb_alt2.4cvd
cfm2.5-r_vn_alt1.4cad
cfm2.5-r_vn_alt1.4cvd
cfm2.5-r_vn_alt2.4cad
cfm2.5-r_vn_alt2.4cvd

where:

cfm2.5-r:

CFM-R derived from CFM 2.5

dv:

Death Valley region

la:

Los Angeles basin region

main:

all other regions

sb:

Santa Barbara channel region

vn:

Ventura basin region

alt1:

first alternative fault model

alt2:

second alternative fault model

4cvd:

four corner data file with variable depths

4cad:

four corner data file with average depths

This data files were generated from tsurf files which are available in this compressed tar archive:

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Copyright 2005 Harvard University
Structural Geology and Earth Resources Group