Fine-scale structure of the 2016-2017 Central Italy Seismic Sequence from data recorded at the Italian National Network

Data Set 

Catalog of 33,983 earthquakes located during the 2016-2017 Central Italy seismic sequence. The velocity model used is the 1D gradient P- and S-wave velocity models (after Carannante et al., 2013). We used the highest quality P- and S-wave arrival times manually picked by analysts of the National Institute of Geophysics and Volcanology (INGV) seismic monitoring room, having an uncertainty lower than 0.6 s.  

Events were located by means of a 2-step procedure: the INGV routine absolute locations computation for all events with ML ≥ 1.5 that occurred in the study area between August 2016 and January 2018, using the method described in Chiaraluce et al. (2017); the determination of relative locations by applying the HypoDD code (Waldhauser, 2001) to the catalog picks and phase delay times measured from waveform cross correlation.

The time domain cross-correlation method (Schaff et al., 2004; Schaff and Waldhauser, 2005) was applied to seismograms of all pairs of events separated by 3 km or less and recorded at common stations.  Seismograms were filtered in the 1-15 Hz frequency range using a 4 pole, zero phase band‐pass Butterworth filter. The correlations measurements were performed on 0.7 s long window for P-waves and 1 s windows for S-waves. Only measurements with correlation coefficients greater than 0.7 were kept, resulting in a total of ~4.4 million P and ~1.1 million S wave delay times. 

We sub-divided the entire dataset in 18 rectangular boxes, containing a maximum of 6000 earthquakes, orthogonal to and centered on the mean strike of the seismic sequence. The overlap between neighboring boxes is 50% with respect to the NW-SE extension. HypoDD is run separately on each box. 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 33,982 events occurring between 24th of August 2016 and 18th of January 2018.

The catalog is in csv format, semicolon separator, ordered by origin time and the header content is the following:

Id-ingv: ingv eventid, useful to link to the QuakeML phase file through the INGV fdsnws/event webservice (http://webservices.ingv.it/swagger-ui/dist/?url=https://ingv.github.io/openapi/fdsnws/event/0.0.1/event.yaml) and to the reported magnitude;

Latitude(°) expressed in decimal degrees;

Longitude(°) expressed in decimal degrees;

Depth(km) hypocentral depth expressed in kilometers;

Year of origin time in the format yyyy;

Month of origin time in the format mm;

Day of origin time in the format dd; 

Hour of origin time in the format hh;

Minute of origin time in the format min;

Second of origin time in the format ??.?????? s;

Magnitude: the value available at the phases downloading time (see Id-ingv fdsnws/event)