Earthquake Explorer goes 3D: A Browser-Based Tool for Interactive Earthquake Visualization

The moment tensor of an earthquake describes the force couples acting at the source location as a symmetric 3x3 matrix, and provides information on orientation and slip direction of the fault failure. Shear failure is represented by a double-couple, for which the trace of the moment tensor is zero and the intermediate eigenvalue is zero, with the corresponding eigenvector termed the neutral axis. In the seismology literature, this tensor is typically visualized in a two-dimensional beachball diagram, a lower-hemisphere projection of a three-dimensional sphere split into four quadrants by two perpendicular great circles oriented according to the eigenvectors of the matrix, such that the neutral axis points to the intersection of the two circles, and the other two eigenvectors point to the centre of each quadrant.

In this contribution we present a new browser-based tool to visualize the moment tensors of earthquakes not just as a two-dimensional projection but as three-dimensional objects. Concretely we show an earthquake as a magnitude-scaled sphere, textured according to its moment tensor, and located at its hypocenter. We provide options to visualize only the double-couple part of the moment tensor, to color the spheres by depth only and to also show earthquakes for which no moment tensor solution has been derived. Additional context is provided by the SLAB2 model of the subduction zones of the earth as well as raster and vector map layers loaded via OGC compliant APIs (WMS/WFS).

The tool runs entirely in a user’s web browser and fetches earthquake data from an FDSN Web Services (FDSNWS) events endpoint in QuakeML format, thus using a standardized API widely-used in the seismology community. While our deployment is currently integrated into the GFZ Earthquake Explorer, using the GEOFON network, it is also compatible with other station networks that provide data via FDSNWS. The visualization is built using the open-source library CesiumJS with custom WebGL shaders that implement the coloring of the spheres as beachballs.

The fact that no specialized software packages are needed also makes the tool suitable for a more general audience beyond scientists from the seismology community.