China Active Faults

This is a repository containing the data and script necessary to run a joint geodetic/geologic block inversion to get slip rates for HimaTibetMap v.2.0, and the results (as of the most recent commit).

Running the inversion

The block inversion uses Oiler. Please see that repository for installation instructions.

Once Oiler has been installed, go into the scripts/ directory, start a julia interpreter in the terminal, and type julia include chn_blocks.jl

First, the code will compile, then the inversion will run.

Accessing the results

The results are stored in the results directory. There are three files:

• block_vels.csv, which is a CSV file that contains the predicted block velocities relative to stable Eurasia. The fields are fid (the block index), lon and lat (the coordinates of the block centroid), and the velocity components with 1-sigma uncertainties, ve, vn, ee, en, and the covariance cen.

• chn_gnss_results.csv, which is a CSV file that contains the predicted GNSS velocities (which are the sum of the block motions and earthquake cycle effects). The fields are lon and lat (the geographic coordinates of each GNSS station), name, fix (the index of the reference frame, 1111 for all, indicating stable Eurasia, mov (the fid of the block), and a number of fields with self-explanatory names denoting the observed, predicted and residual GNSS velocities with 1-sigma uncertainties.

• chn_faults_out.geojson, which is a LineString (polyline) GIS file with the fault traces, additional geometric information, estimated slip rates, and some other metadata.

The chn_faults_out.geojson file has the following attributes:

• fid: the ID of the feature (the fault trace).
• dip: the average dip of the fault. Note that 89 is the max, so that hw and fw are defined.
• dip_dir: the cardinal direction the fault dips in.
• usd: the upper seismogenic locking depth (km) in the inverison.
• lsd: the lower seismogenic locking depth (km) in the inversion.
• hw: the fid of the block in the hanging wall.
• fw: the fid of the block in the footwall.
• name: the name of the fault, if known (may be empty).
• dextral_rate: the dextral slip rate of the fault, in mm/yr. Sinistral negative.
• dextral_err: the 1-s.d. uncertainty of the dextral slip rate, in mm/yr.
• extension_rate: the extensional slip rate of the fault, in mm/yr. Contraction is negative. Note that this is also the horizontal extension rate across the fault.
• extension_err: the 1-s.d. uncertainty of the extensional slip rate, in mm/yr.
• cde: the covariance of the dextral_err and extension_err.
• net_slip_rate: the vector magnitude of the slip rate, in mm/yr.
• net_slip_rate_err: the 1-s.d. uncertainty of the net_slip_rate.

Visualizing the block motions with the interactive web viewer

The best way to understand the block results is to use an interactive viewer that is provided. This uses a web browser and requires the user to start a web server; if the user has Python installed, this should work without further configuration.

In a terminal, go into the web_viewer/ and type

bash python -m http.server

and a web server should start from this directory, serving pages at localhost:8000. Then, type localhost:8000 in the browser to see the page.

A blank globe (latitude and longitude lines) should pop up, and there should be a button that says 'Draw Blocks', and a slider that says 'Ma'. Click on 'Draw Blocks', and after a little while (a minute or two, for the first time), the block model should appear on the globe. You can click on it and move it around, zoom in and out with the mouse, etc. Perhaps more importantly, you can move the 'Ma' slider back and forth to simulate instantaneous block motions projected forward or backward 5 million years in time. Please note this is not meant to be a real reconstruction or project, but simply a way to visualize the current block motions better!