Bragato, P. L.

Gentili, S.

Pesaresi, D.

Snidarcig, A.

Earth-prints Repository

 FAAS and Antelope: two automatic earthquake location systems in the 
northeastern Italy and surrounding areas
1 1 1,2 1
S. Gentili ,  P. L. Bragato , D. Pesaresi  and  A. Snidarcig
(1) Ist. Naz. di Oceanografia e di Geofisica Sperimentale (OGS), (2) Ist. Naz. Di Geofisica e Vulcanologia (INGV)
Location: regarding the accuracy in location, the systematic error of both FAAS and 
Antelope relative to the OGS bulletin (m in figures 13-18) is of the order or smaller than 1 
km. Using the same method described above for the picks and considering the small 
area monitored by FAAS, we have estimated the absolute variance of the locations in the 
2
three data sets referred to the real, unknown epicenters: var (Antelope)=30km  
LONG ,
2 2 2 2
var (Antelope)=16 km , var (FAAS)=7 km var (FAAS)=4 km ,v ar (OGS)=0 km , 
LAT LONG , LAT LONG  
2.
var (OGS)=2 km
LAT
The variance is much higher for Antelope due to the low grid resolution.
Magnitude: In order to understand if the M  and M of the three system are coherent, we 
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plot the comparison among the magnitude of the different databases. The OGS bulletin 
reports M , which is also computed by FAAS. Figures 19 shows how FAAS underestimates 
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M  by about 0.2 (Gentili et al. 2006), which is within the standard calibration deviation 
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(about 0.3). Both Antelope and FAAS compute M  (Figure 20): the latter tends to 
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underestimate M  and such result is mainly related to the use of a different attenuation 
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law. 
Event detection: the capability of detecting earthquakes depending on their magnitude has been analyzed (maps in the Figures 4-6 and histograms in the Figures 7-18). For the two systems we have 
considered the area monitored by FAAS (coordinates: LON=[12-14],LAT=[45.5-47]). For Antelope we have also considered  the larger trans-national area of interest for the INTERREG project (coordinates: 
LON=[12.1-15.7], LAT=[44.5-47.3]). It emerges that for the smaller area, the maximum magnitude of not detected earthquakes is 2.7 for FAAS and 2.9 for Antelope. For the larger area, the maximum 
magnitude of the events lost by Antelope is 3.3.
Fig 19 Fig 20
Picking: P waves picking times of FAAS and Antelope have been compared with those in the OGS database. From the Figures 
2 and 3 it is possible to see that both FAAS and Antelope pick some hundredth of seconds after the OGS database. The 
mean and the variance have been calculated considering the entire data set and after eliminating the outliers (picks 
farther than 1s from the corresponding manual ones). Besides the variance relative to the manual picks, following Gentili 
and Bragato (2006) we have estimated the absolute variance of the three data sets (i.e. the variance of the difference 
between the real, unknown arrival times and the picked ones). In general, given two independent data sets A and B, it holds 
the relation var(A-B)=var(A)+var(B). Combining in a system the three equations derived for the available data sets, we have 
obtained:
2 2 2
var(Antelope)=0.018s ,   var(FAAS)=0.016s ,   var(OGS)=0,011s
Fig 2 Fig 3
Fig 6
Fig 4
Fig 5
Fig 10Fig 7
Fig 8 Fig 11
Fig 9 Fig 12 Fig 15
Fig 14
Fig 13
Fig. 18
Fig 17
Fig 16
Centro di Ricerche
Sismologiche
ISTITUTO NAZIONALE
DI OCEANOGRAFIA E
DI GEOFISICA SPERIMENTALE
Fig. 1
Since 1996 at the Centro di Ricerche Sismologiche (CRS, http://www.crs.inogs.it) of the Istituto Nazionale di Oceanografia e di Geofisica 
Sperimentale (OGS) it is active the Friuli Automatic Alert System which monitors the Friuli-Venezia Giulia region (NE Italy) and  surrounding 
areas based on 21 short period stations (red triangles in Fig.1, Priolo et al.; 2005). 
Since 2002 the CRS is involved in the EU Interreg IIIA project “Trans-national seismological networks in the South-Eastern Alps” together to 
other four institutions monitoring the area (Bragato et al, 2003): DST of Trieste University and Civil Protection of Regione Autonoma Friuli-
Venezia Giulia (Italy), ARSO (Slovenia), and ZAMG (Austria). The Antelope software suite has been chosen as the common basis for real-time 
data exchange, rapid earthquakes location and alerting. Each institution has an instance of the system running at its data center and 
acquires data in near real-time from its stations and those of the other partners (Fig.1).   
In this poster, the FAAS and Antelope performances are analyzed. Their procedures for picking, earthquake detection, location and 
magnitude estimation are shortly described and the results compared with the manually revised data available in the NEI (North Eastern 
Italy) network bulletin (OGS database) from December 2005 to July 2006. We analyze the detection capabilities, quality of time arrival picks 
and locations and the differences among the various magnitudes (M  and M ). In particular, for pickings and locations we furnish an 
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absolute estimation of the error in respect to the real, unknown values.
Processing steps. FAAS detects events by a STA/LTA trigger on remote stations. If there is a coincidence between at least 4 stations, the event is analyzed by picking P and S arrivals. The location is 
performed by Hypo71 program, while two magnitude values are supplied: the duration magnitude M  by using the formula of Rebez and Renner (1991) and the local magnitude M  according to the 
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formula by Bakun and Joyner (1984).
Antelope detects events by STA/LTA algorithm and the association is based on location by grid search; only P arrivals are used. The location is performed by grid search over 87x81 nodes for an extension 
o o
of 7x6.4 degrees (corresponding to cells of 8.9 km in longitude and 8.7 km in latitude) centered in Lat=46.26 , Lon=13.28  with depth steps at 0, 2, 4, 6, 8, 10, 12, 14, 16, 20 and  24 km, using the 1D 
uniform velocity model IASPEI91. The location procedure has been set-up and tuned mainly at DST in Trieste. The magnitude M  is estimated using the program “orbampmag” developed by Nikolaus 
L
Horn at ZAMG in Vienna.
References Bragato P.L., Costa G., Horn N., Michelini A., Mocnic G. And Zivcic M.; 2003: Real-time data and network integration in the southern Alps, Geoph. 
Res. Abstracts, 5, paper number 08690.
Gentili S. and Bragato P.L.; 2006: A neural-tree-based system for automatic location of earthquakes in Northeastern Italy, Journal of 
Seismology, Vol 10, No. 1, pp. 73-89


FAAS and Antelope: two automatic earthquake location systems in the Northeastern Italy and surrounding areas

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FAAS and Antelope: two automatic earthquake location systems in the Northeastern Italy and surrounding areas

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