SCEC Award Number 14060 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Forecasting focal mechanisms and assessing their skill
Investigator(s)
Name Organization
David Jackson University of California, Los Angeles Yan Kagan University of California, Los Angeles
Other Participants
SCEC Priorities 2a, 2b, 2d SCEC Groups Seismology, CSEP, EFP
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Forecasts of the focal mechanisms of future earthquakes are important for seismic hazard estimates and other models of earthquake occurrence. The method was originally proposed by Kagan & Jackson in 1994. An important problem is how to evaluate the skill of the focal mechanism forecast and optimize this forecast. In our recent paper (Kagan & Jackson, 2014) we started to investigate this problem. In previous publications we reported forecasts of 0.5 degrees spatial resolution, covering the latitude range from -75 to +75 degrees, based on the Global Central Moment Tensor earthquake catalog. In this project we perform a high-resolution global forecast of earthquake rate density as a function of location, magnitude, and focal mechanism. In these forecasts we've improved the spatial resolution to 0.1 degrees and the latitude range from pole to pole. Our focal mechanism estimates require distance-weighted combinations of observed focal mechanisms within 1000 km of each grid point. Simultaneously we calculate an average rotation angle between the forecasted mechanism and all the surrounding mechanisms. This average angle reveals the level of tectonic complexity of a region and indicates the potential accuracy of the prediction. Thus deformation complexity displays itself in the average rotation angle and in the Gamma-index. Initially we have used the GCMT catalog, which has a significant number of shallow earthquakes, that allow us to test forecast verification procedures. However, the large number of parameters needed to evaluate future focal mechanisms makes such work time-intensive. We constructed a simple tentative solution but extensive additional theoretical and statistical analysis is needed.
Intellectual Merit Our ultimate objective is to construct a model for computing
and testing the probability that an earthquake of any
size will occur within a specified region and time and determine its
possible focal mechanism.
The advantage of such our approach is that earthquake rate
prediction can be adequately combined with focal mechanism
forecast, if both are based on the likelihood scores,
resulting in a general forecast optimization.
These aims correspond specifically to SCEC research objectives.
Broader Impacts Evaluating the future rate of earthquake occurrence in
time-space-magnitude-focal mechanism orientation in any given region is
important for designing critical facilities, for comparing earthquake and
tectonic moment rates, and for understanding the relationship of earthquakes to
stress, material properties, fault and plate geometry, and many other features
which might affect earthquake rupture. The developed method can be used by
engineers and decision makers to estimate earthquake hazards. This project
provided technical experience and training to UCLA graduate students Anne
Strader.
Exemplary Figure Figure 1

Distribution of rotation angles
for shallow (depth 0--70~km) earthquakes
in the GCMT catalog, 1977--2007/2008--2012, = 6$~km,
latitude range $[ 75^\circ S-75^\circ N ]$, earthquake number
=1069$.
Scatterplot of interdependence of the predicted $\Phi_1$ and
observed $\Phi_2$ angles (Eqs.~\ref{eq0},\ref{eq-1}).
Both angles are calculated for the cells in which earthquakes
of the test period occurred.
Blue lines from top to bottom are 75\%, 50\%, and 25\%
$\Phi_2$ quantiles for a $\Phi_1$ angle subdivision with equal
number of events in 10 subsets.