SCEC CBM - Mojave trial

The SCEC Community Block Model is assembled from a subset of CFM faults and from 3 horizons - the topography, the depth of the seismogenic crust and the Moho. These elements divide the crust into two layers with 10 blocks each. The blocks are named A, B, C, D, E, F, G, H, I and J followed by an "u" for blocks in the upper layer or a "l" for blocks in the lower layer. All names in TSurf file headers are prefixed with "cbm".

Fig. 1. CBM horizons: topography, depth of seismogenic crust and Moho. The crust is subdivided into 10 blocks A to J.

There are 3 representations of the blocks derived from the CFM fault represenations:

raw blocks: from crosscutting, trimming and reassembling CFM
remeshed blocks: from retriangulating, crosscutting and reassembling
regular grid: brick volumes from sampling rectangular grid with blocks

The raw and remeshed block representation is provided with TSurfs, in the CFM file format. The regular grid representation is provided in an ASCII file which contains the location of each brick in a block.

Raw Blocks

As a result of the widely varying resolution of the original CFM TSurfs, the sizes and shapes of the triangles in the block meshes varies widely as well. The crosscutting procedure additionally can produce extreme aspect ratios and even degenerate triangles with zero area. Each block is defined by an upper and lower surface and segments of faults. The blocks are provided in two ways: as an assembly of TSurfs in a file archive and as a specification of which fault segments define the blocks. The fault segments and the lower and upper surfaces are contained in separate files. Here is a figure which shows the fault segments and their names:

Fig. 2. CBM faults and model boundaries: They are numbered 1 to 12 and each is subdivided into up to 5 block faces a to e.

In the raw blocks tar archive there are 3 TSurf files which contain the horizons as upper and lower surface for each block, topo.ts, seis.ts and moho.ts. The names for the individual TSurfs for each block are cbmTA to cbmTJ in topo.ts, cbmSA to cbmSJ in seis.ts and cbmMA to cbmMJ in moho.ts. The fault segments are contained in faults.ts and are named cbmNNxi where NN can be 1 to 12, x "a" to "e" and i "u" or "l".

Here is the list which specifies which fault segments compose a block:


block	fault	segment
A	1	a
	8	a
	3	a
	2
	10	a
B	3	a
	8	b
	4	a
	4	b
	10	c
	3	b
C	4	a
	8	c
	5
	9	a
D	5
	8	d
	6	a
	9	b


block	fault	segment
E	6	a
	8	e
	7
	12	c
	6	b
F	2
	3	b
G	10	b
	4	b
	9	a
	9	b
	6	b
	12	b
	11	b
	4	c
H	1	b
	10	a
	10	b
	10	c
	4	c
	11	a


block	fault	segment
I	1	c
	11	a
	4	d
J	1	d
	4	d
	11	b
	12	a

In addition, the archive contains two more sets of files. cbmblAi to cbmblJi where "i" can be "u" or "l" are TSurfs which contain all faces for each block A to J. cbmAi to cbmJi are TSurfs for which all surfaces of each block were joined together into a single continuous surface which may have defects such as small holes.

Remeshed Blocks

The remeshed blocks differ from the raw blocks in that triangle size are much less varied with a goal of 1km size. Also, triangles with high aspect ratios are restricted to the borders and are exclusively a result from crosscutting triangulated meshes.

Fig. 3. Typical triangle sizes (1km) and shapes at block faces and edges.

The remeshed blocks archive is organized in much the same way as the raw blocks archive and the naming convention is in parallel. There are TSurfs cbmAi to cbmJi for which all faces of each block were joined into a continuous single surface. These meshes have less defects than the raw joined meshes.

Regular Grid

This block representation consists of a sampling of a rectangular volume in regular intervals with the remeshed blocks. The interval is 1km in each dimension and the dimensions are oriented North-South, East-West and Up-Down. The regular grid archive contains just 1 file with entries for all of the blocks. The blocks are named gridAi to gridJi. The file lists in the first column the block name and in the following columns the locations of the centerpoints of the 1km cubes which are inside this block.

Fig. 4. CBM blocks in a regular 1kmx1kmx1km grid. Block H is removed in this figure.

Download

Here are the three representations for download in tar archives:

raw blocks: cbm_mo_raw.tar.gz
remeshed blocks: cbm_mo_remeshed.tar.gz
regular grid: cbm_mo_raw.tar.gz