The 2009 Mw6.1 L'Aquila normal fault system imaged by 64,051 high-precision foreshock and aftershock locations.

The earthquake catalogue is composed by 64,051 high-precision foreshock and aftershock recorded during the Mw6.1 2009 L'Aquila (Central Italy) normal faulting seismic sequence. The catalog includes events occurred between 1st of January and 31st December 2009. The completeness magnitude is 0.7. Earthquake locations were obtained by combining an automatic picking procedure for P and S waves, together with cross-correlation and double-difference location methods. 

Seismic data were recorded at a very dense local network composed of 67 three-component seismic stations (20 permanent stations of the Italian National Network located within 80 km from the epicentral area and 47 temporary stations installed soon after the occurrence of the main shock [Margheriti et al., 2011]). 

Earthquakes were extracted by the continuous recordings by applying a detection algorithm to all stations, based on the classical STA/LTA coincidence-sum algorithm applied to the trace of the 3C covariance matrix. To these events, we applied an automatic picking algorithm (Manneken Pix) [Di Stefano et al., 2006] able to provide about 1.9 million P-wave and 503,000 S-wave accurate readings, with an estimation of the measurement errors. 

We applied a time domain cross-correlation method (Schaff and Waldhauser, 2005) to all event pairs with separation distances ≤ 5 km at all stations that recorded the pair. Seismograms were filtered in the 1-15 Hz frequency range using a 4 pole, zero phase band‐pass Butterworth filter. We selected measurements with correlation coefficients greater than 0.85, resulting in a total of ~190 million P and ~85 million S-wave delay times. 

Earthquakes were located following a two steps procedure. Initial locations for 133,236 events were computed with the Hypoellipse code [Lahr , 1989] using a 1D P-wave gradient velocity model optimized for the area [Chiaraluce et al., 2011]. In the second step, we computed relative locations by applying the large scale double-difference method described in Waldhauser and Schaff, (2008) to the catalog picks and phase delay times measured from waveform cross correlation. The entire dataset was sub-divided in 84 rectangular overlapping boxes, containing a maximum of 3000 earthquakes, orthogonal to the mean strike of the seismic sequence. Resulting relative locations from all boxes were combined into a single catalog, computing the weighted mean of double hypocenters in the overlapping regions (Waldhauser and Schaff, 2008). 

The final double-difference catalog includes 64,051 events. A subset made of 51,271 earthquakes (i.e., 80% of the whole dataset) indicates highly correlated earthquakes, having at least 10 P-waves and 5 S-waves correlated phases with at least one other event. Highly correlated events (flag=1 in the attached file) mostly occur on the major fault segments, while poorly correlated earthquakes (flag=0 in the attached file) mostly occur in the volume around the major faults.

The attached file is a plain text with ";" separator and .csv extension.

Here below the header is explained.

id_dd: the hypoDD unique event identifier

origin_time: date of the origin time in the format YYYY-MM-DD[T]hh:mm:ss.msec

lat: hypocenter latitude expressed in degrees 

lon: hypocenter longitude east of Greenwich, expressed in degrees

dep: hypocenter depth expressed in km 

mag: magnitude (pure number)

flag: 1 for highly correlated earthquakes; 0 for poorly correlated earthquakes.