1. AGU fall meeting, December 5-9, 2011, San Francisco INGV Spatial organization of foreshocks as a tool for forecasting large earthquakes E. Lippiello 1, W. Marzocchi 2, L. De Arcangelis 3, C. Godano 1 1- Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy 2- Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 3- Dipartimento Scienze Geologiche, Università "Roma TRE", Rome, Italy The research was developed partially within the Strategies and tools for Real-Time Earthquake Risk Reduction (REAKT; http://www.reaktproject.eu). REAKT is funded by the European Community via the Seventh Framework Program for Research (FP7),with contract no.282862 Lippiello et al, 2012; Scientific Reports, 2, 846

2. AGU fall meeting, December 5-9, 2011, San Francisco INGV Aim of the talk The aim is to investigate if foreshocks of large earthquakes have distinctive features with respect to regular seismic sequences. If so, could we profitably use these features to improve our forecasting capabilities? The two parts of the talk 1. Analysis of the foreshocks and aftershocks sequences of “small” mainshocks in Southern California (SOCAL). 2. Application of the results of point 1 to forecast M>6 earthquakes in SOCAL

3. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks The catalog: we use the Shearer et al (2005) seismic catalog for Southern California (1984-2002). Very accurate epicenter location (<0.1Km) and low completeness magnitude (mc=2) The mainshocks: we use the Felzer & Brodsky (2006) selection criterion. We analyze three mainshock classes M2 maisnhocks with 2<M<3 (black color) M3 maisnhocks with 2<M<3 (red color) M4 maisnhocks with 2<M<3 (green color)

4. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks Is the method to identify mainshocks reliable? A perfect model would require that some earthquakes are “really” mainshocks. If not, all mainshock selections will be necessarily model-dependent. Two questions: 1. Are the mainshocks identified compatible with what we generally consider typical features of a mainshock? (e.g., the time-distribution of foreshocks and aftershocks) 2. Are the results found “real”? Or do they depend on the mainshock selection model?

5. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks Typical temporal features of aftershocks and foreshocks

6. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks LINEAR DENSITY DISTRIBUTION in the real Catalog

7. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks LINEAR DENSITY DISTRIBUTION in the real Catalog

8. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks LINEAR DENSITY DISTRIBUTION in the real Catalog

9. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks LINEAR DENSITY DISTRIBUTION in ETAS simulated catalogs

10. AGU fall meeting, December 5-9, 2011, San Francisco INGV 1. Foreshocks & aftershocks The mainshock magnititude is encoded in the foreshocks' spatial organization

11. AGU fall meeting, December 5-9, 2011, San Francisco INGV 2. Forecasting M>6 earthquakes Daily probability for M6+ earthquakes is given by the combination of ETAS probabilities (Zhuang et al., 2004, 2005, 2008) and a factor who takes into account the spatial organization of foreshocks We use the results of point 1 to forecast the six M>6 earthquakes in the SOCAL seismic catalog

12. AGU fall meeting, December 5-9, 2011, San Francisco INGV 2. Forecasting M>6 earthquakes Comparison of the forecasting performances versus RI model (Rundle et al., 2002) Model Equivalent Confidence level=99% Average gain = 50.7

13. AGU fall meeting, December 5-9, 2011, San Francisco INGV 2. Forecasting M>6 earthquakes Comparison of the forecasting performances versus ETAS (Zhuang et al., 2004, 2005, 2008) Average gain = 4.5

14. AGU fall meeting, December 5-9, 2011, San Francisco INGV 2. Forecasting M>6 earthquakes DAILY OCCURRENCE PROBABILITY of M>6 earthquakes within a cell 0.04 o x0.04 o

15. AGU fall meeting, December 5-9, 2011, San Francisco INGV 2. Forecasting M>6 earthquakes DAILY OCCURRENCE PROBABILITY of M>6 earthquakes within a cell 0.04 o x0.04 o

16. AGU fall meeting, December 5-9, 2011, San Francisco INGV Final remarks  The organization in space of seismicity before a mainshock contains information about the magnitude of the mainshock itself.  The capability to forecast M6+ earthquakes is significantly improved with respect to a pure ETAS model when the spatial organization of foreshocks is included. The future...  Verifying the forecasting performances in Japan and Italy (keeping the same rules)  Implementing the code into a formal CSEP testing laboratory