SCEC Project Details
SCEC Award Number  14060  View PDF  
Proposal Category  Collaborative Proposal (Integration and Theory)  
Proposal Title  Forecasting focal mechanisms and assessing their skill  
Investigator(s) 


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 highresolution 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 distanceweighted 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 Gammaindex. 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 timeintensive. 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 timespacemagnitudefocal 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 070~km) earthquakes in the GCMT catalog, 19772007/20082012, = 6$~km, latitude range $[ 75^\circ S75^\circ N ]$, earthquake number =1069$. Scatterplot of interdependence of the predicted $\Phi_1$ and observed $\Phi_2$ angles (Eqs.~\ref{eq0},\ref{eq1}). 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. 