Outcomes from application of Regional and Onsite Early Warning systems to the 2016,

August 24, Central Italy earthquakeA. Zollo, A. Caruso, M. Cattaneo, S. Colombelli, L. Elia, G. Festa, C. Martino, S. Marzorati, M. Picozzi and RISSCLab Group.

In this short presentation we analyze the performance of the two software for earthquake early warning developed by the research group at the Seismological Laboratory of the Dept. of Physics, University of Naples: the network-based PRESTo (Probabilistic and Evolutionary EW System) and the onsite SAVE (On Site Alert Level) in occasion of the 2016, August 24, Amatrice Earthquake. We applied on-line and off-line the methods to seismic waveforms recorded by the network operated by INGV and to that operated by DPC.

PRESTo & SAVE EEW

EEW systems are under testing at Italian NFOsIrpinia and TABOO

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Alert at distantsites(blind zone > 15 km)

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In this slide, the time history of the alerts issued by the network-based method (PRESTo) and the on-site method (SAVE) are shown. In PRESTo the alert results from the analysis of signals recorded by a network of stations and the prompt estimation of location, magnitude and ground shaking prediction through specific GMPEs. In SAVE the alert is obtained from a single station analysis and it is based on the direct estimation of the predicted intensity at the site as given by the measure of the first P-wave amplitude. The blind zone is the region within which the strong shaking waves arrive before the alert. The onsite method allows to drastically reducing the blind zone. The two systems are operated at the Near Fault Observatories (NFOs) in Italy of Irpinia and TABOO.

PRESTo – Real Time @ANCONAFirst Alert at 01:36:46.3 UTC

• 11.4 seconds after 1st pick (near Amatrice)• 14.3 seconds after origin time (INGV)• 6 picks required (orange stations)

Comparison to INGV bulletinLocation• 1.8 km from real epicenterMagnitude:• -0.2 from real magnitude

Latency (3-4 seconds, up to 10-20 sec)coupled with the low density of data inthe epicentral area

Since July 2015, PRESTo runs at the INGV network control center of Ancona, to investigate the performances of the EEW system both at the NFO TABOO and on the part of the national network located in Central Italy. This activity was promoted in the framework of the EPOS project. The software was connected to the real-time data streaming from the INGV stations and was set to declare an event if 6 picks would occur within 3 seconds. The system was running during the Amatrice Earthquake and provided an alert 11.4 s after the first P-pick and 14.3 s after the origin time. The estimated location is very close to the one released by the INGV bulletin (epicentral distance < 2 km), while the magnitude was underestimated by 0.2, as the system provided an initial M = 5.8. The final estimation from PRESTo was instead M = 6.1. The large delay in the alert was due to the latency introduced by data packetization (2-3s) and data transmission (up to 20s for some stations connected to the control center via Wireless and Satellite), and because some data was not usable (clipped signals).

PRESTo – Playback RAN

This slide presents the performance of PRESTo running on the RAN, the national accelerometric network operated by the Civil Protection Department (DPC). The accelerometric network is not currently providing data in real-time mode. Therefore, the analysis has been carried out offline, that is to say, the playback of PRESTo with the RAN recordings simulates the real-time analysis, but without delays due to the data transmission. Playback animation available here: http://isnet.fisica.unina.it/reports/Central_Italy_2016_RISSC_Early_Warning.gif

Performances of PRESTo @ RAN

First Alert at 01:36:38.6 UTC

• 3.8 seconds after 1st pick (at Amatrice)• 6.6 seconds after origin time (INGV)• 5 picks required (orange stations)

Comparison to INGV bulletinLocation• 1.7 km from real epicenter

Magnitude:• -0.2 from real magnitude

In terms of location and magnitude estimates, the performance of PRESTo on the RAN is similar to the real-time performance with the INGV network. It is interesting to note that in the ideal condition of no delay for data transmission, the first alert is released 3.8 seconds after the 1st pick at Amatrice, and only 6.6 seconds after the origin time.

PRESTo – prediction error

Evaluation of prediction error on PGV and Intensity (IMM) at the recording sites. A description of the ground shaking would have been available after 6-7 s after OT

What would have been the accuracy of PRESTo in predicting the instrumental intensity (IMM) at the sites of the network? Here the analysis, with the plot (on the left) of the prediction error of PGV, which is the proxy parameter used to estimate the IMM. The prediction error of PGV, shown as a function of distance (left-plot), is computed as the difference between observed and predicted logarithmic peak motion amplitude. The prediction error by PRESTo remains stable with distance, and generally distributed around 0 (mean value 0.06, solid line), showing a maximum variability of ±0.33 (dashed lines), which is comparable to fluctuations observed for standard GMPEs (e.g. Akkar and Bommer, 2010). On the right figure, a map showing the performance of the system in terms of correct predictions (dark and light green), underestimated predictions (red) and overestimated predictions (yellow). The map shows that, in the epicentral area, most of intensities are correctly estimated, with relatively small percentages of underestimated alarms (about 13%) and overestimated alarms (about 15%)

SAVE – playback RAN

In the next two slides we show the analysis and performance of the onsite system SAVE. This is a playback of the seismic record acquired at the station AMT of the RAN. The onsite method estimates the intensity through the predicted PGV at the site, the latter parameter related to the P-wave peak displacement. The joint measurement of the P-peak displacement and the predominant period allows getting estimations of the magnitude and distance, which are provided according to a broad classification, given the expected uncertainty on these parameters as obtained from a single station. Finally the alert level (e.g. Zollo et al, 2010) is given by the combination of the measured peak displacement and predominant period. You can see in the screenshot that SAVE detects the event and, after only three seconds form the P-wave arrival time, the event is classified as near to the site, with moderate magnitude and an expected Intensity of VIII (i.e. IMM is estimated by the predicted PGV through the Faenza L. and A. Michelini [2010] relationship). The provided alert level is the highest.

11oE 12oE 13oE 14oE 15oE 41oN

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Alert Performance (IMM >= VI)

Damage

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Missed AlertFalse AlertAlert IMM > damageAlert IMM < damage

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maxlt PGV alertT T T= −

Lead time analysis

Here we show the performance of the onsite system SAVE as obtained from an off-line analysis of RAN records of the Amatrice mainshock. The performance of the SAVE system is evaluated by setting a threshold for the instrumental intensity (IMM>=VI). The correct intensity prediction is obtained in 83% of the cases, while 12% are the false alarms and only 4% the missed alarms. The number of false alerts is low and the map shows that they are close to the epicentral area, which leads them to be in favor of security. The few missed alerts are observed along the rupture directivity direction and at a relatively large distance, at sites where anyhow no significant damage was observed. The lead times are defined as the difference between the time at which the peak motion is observed minus the time of the alert. The Time vs. Distance plot shows that within 20 km the available lead time is between 1 and 4 seconds, while for sites at distances larger than 40 km it increases above 10 seconds