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Lippiello et al, 2012; Scientific Reports , 2 , 846 . 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

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Lippiello et al, 2012; Scientific Reports, 2, 846

Spatial organization of foreshocks as a tool for forecasting large earthquakes

E. Lippiello1, W. Marzocchi2, L. De Arcangelis3, C. Godano1

1- IstitutoNazionalediGeofisicaeVulcanologia, Rome, Italy

2- IstitutoNazionalediGeofisicaeVulcanologia, 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

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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

Analysis of the foreshocks and aftershocks sequences of “small” mainshocks in Southern California (SOCAL).

Application of the results of point 1 to forecast M>6 earthquakes in SOCAL

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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 completenessmagnitude (mc=2)

The mainshocks: weuse the Felzer & Brodsky (2006) selectioncriterion. We analyze three mainshock classes

M2maisnhockswith2<M<3 (black color)

M3maisnhockswith2<M<3 (red color)

M4maisnhockswith2<M<3 (green color)

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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?

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1. Foreshocks & aftershocks

Typical temporal features of aftershocks and foreshocks

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1. Foreshocks & aftershocks

LINEAR DENSITY DISTRIBUTION in the realCatalog

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1. Foreshocks & aftershocks

LINEAR DENSITY DISTRIBUTION in the realCatalog

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1. Foreshocks & aftershocks

LINEAR DENSITY DISTRIBUTION in the realCatalog

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1. Foreshocks & aftershocks

LINEAR DENSITY DISTRIBUTION in ETAS simulatedcatalogs

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1. Foreshocks & aftershocks

The mainshockmagnititudeisencoded in the foreshocks' spatialorganization

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2. Forecasting M>6 earthquakes

Weuse the resultsofpoint1toforecast the sixM>6earthquakes in the SOCAL seismiccatalog

Dailyprobabilityfor M6+ earthquakesisgivenby the combinationof ETAS probabilities (Zhuanget al., 2004, 2005, 2008) and a factorwhotakesinto account the spatialorganizationofforeshocks

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2. Forecasting M>6 earthquakes

Comparisonof the forecastingperformances versus RI model (Rundleet al., 2002)

Average gain = 50.7

ModelEquivalent

Confidence level=99%

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2. Forecasting M>6 earthquakes

Comparisonof the forecastingperformances versus ETAS (Zhuanget al., 2004, 2005, 2008)

Average gain = 4.5

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2. Forecasting M>6 earthquakes

DAILY OCCURRENCE PROBABILITY ofM>6earthquakeswithin a cell 0.04ox0.04o

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2. Forecasting M>6 earthquakes

DAILY OCCURRENCE PROBABILITY ofM>6earthquakeswithin a cell 0.04ox0.04o

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Final remarks

  • The organization in spaceofseismicitybefore a mainshockcontains information about the magnitudeof the mainshockitself.
  • The capabilitytoforecast M6+ earthquakesissignificantlyimprovedwithrespectto a pure ETAS modelwhen the spatialorganizationofforeshocksisincluded.
  • The future...
  • Verifying the forecastingperformances in Japan and Italy (keeping the samerules)
  • Implementing the code into a formal CSEP testinglaboratory