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SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY) Istituto Nazionale di Geofisica e Vulcanologia, sezione Milano - Pavia Istituto.

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Presentation on theme: "SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY) Istituto Nazionale di Geofisica e Vulcanologia, sezione Milano - Pavia Istituto."— Presentation transcript:

1 SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY) Istituto Nazionale di Geofisica e Vulcanologia, sezione Milano - Pavia Istituto Nazionale di Geofisica e Vulcanologia 30° convegno nazionale GNGTS, Trieste, novembre 2011 Luzi L., Massa M., Puglia R., Pacor F.

2 30° convegno nazionale GNGTS, Trieste, novembre 2011 SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY) Earthquakes data set from January to April 2009 Spectral analyses on noise and seismic events Detection of surface waves and polarization phenomena DPC-S4 Project , coordinated by INGV-MI Anomalous response of ITACA sites Active geophysical surveys Passive seismic investigations (in collaboration to GFZ, Potsdam, Germany)

3 30° convegno nazionale GNGTS, Trieste, novembre 2011 Seismic hazard for Norcia (OPCM 3519, 28/04/2006) 10% of probability (T 475 yr) to exceede PGA (on rock site) in the next 50 yr between and g (http://esse1- gis.mi.ingv.it/) Historical seismicity (Io >= 6) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

4 30° convegno nazionale GNGTS, Trieste, novembre 2011 Several RAN stations were installed in the basin. On the basis of EC8 provisions the installation sites were classified as B,C or D NRC (since 1979) -> EC8 B category m/s (Vs30) Di Alessandro et al., 2008 CL-VII Luzi et al., 2011 F-1 (HVSR amplitude 1.1 (+/- 0.5) between station error/between station sigma evaluated introducing different site classification schemes in ad-hoc developped GMPE ( from Bindi et al., BEE 2011 ) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

5 30° convegno nazionale GNGTS, Trieste, novembre 2011 Passive seismic investigation 1 microtremor array close to station 12 (15 Mark-1s, inter-distance from 4.6 to 83 m, sampling 200 Hz, 2h) Temporary velocimetric network (15 Mark-1s coupled to 24 bits Earth Data Logger, sampling 100 Hz) Active geophysical survey 2 seismic reflection surveys 1 down-hole test close to station 14 (depth of 60 m) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

6 30° convegno nazionale GNGTS, Trieste, novembre 2011 Down-hole (Vs30 = 664 m/s) Reflection profile Microtremor array (Vs30 = 557 m/s) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

7 30° convegno nazionale GNGTS, Trieste, novembre 2011 Temporary seismic network (January-April 2009) 15 velocimeters 15 Mark-1s coupled to 24 bits Earth Data Logger Data set About 200 selected (S2N > 2.5) seismic events with 2 < ML < 5.9 and epicentral distance up to 100 km SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

8 30° convegno nazionale GNGTS, Trieste, novembre 2011 Data processing Location and ML were obtained from Automatic procedure to select the events based on STA/LTA Deconvolution of signal using the sensor response Filtering using a 2 nd order a-causal Butterworth filter, Hz Manual picking to select P and S arrivals Selection of S-coda (twice the S wave travel time) FFT were calculated and smoothed using Konno and Omachi (1998) with b=40 SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

9 30° convegno nazionale GNGTS, Trieste, novembre 2011 Signals : N = noise ; C = S-coda ; S = S phase Stations: 04 = plain ; 01 = plain ; 11 = reference SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

10 30° convegno nazionale GNGTS, Trieste, novembre 2011 SSR on S-phase for the stations installed in the basin (0.8 Hz, direction N°140) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

11 30° convegno nazionale GNGTS, Trieste, novembre 2011 SSR on S-phase for the stations installed on alluvial fan (2 Hz, direction N°140) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

12 Vertical SSR for station installed in the basin Vertical SSR for station installed on alluvial fan 30° convegno nazionale GNGTS, Trieste, novembre 2011 SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

13 30° convegno nazionale GNGTS, Trieste, novembre 2011 SSR vs. HVSR and S-phase vs. coda S-pahse Amplitude Coda amplitudeHVSR Amplitude Amplitude SSR (H) f 0 Coda f 0 S-phase f 0 Coda SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

14 30° convegno nazionale GNGTS, Trieste, novembre 2011 Example of S-Transform for stations 1 and 5, installed in the basin (02:37:04) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

15 30° convegno nazionale GNGTS, Trieste, novembre 2011 Example of S-Transform for stations 6 and 11, installed on alluvial fan and limestone respectively (02:37:04) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

16 30° convegno nazionale GNGTS, Trieste, novembre 2011 Esempio di Lag Cross Correlation da definire SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

17 30° convegno nazionale GNGTS, Trieste, novembre 2011 SSRs for the stations installed in the basin (1,4,5,10,12) evidence an amplification peak around 0.8 Hz, with preferential direction of amplification N140° SSRs for the station installed on alluvial fan (3,6,13,14,15) evidence a first amplification peak at 2 Hz (N140°) and a second peak around 6 Hz (N30°) Due to vertical amplifications HVSRs and are not able to well highlight the amplification peak at low frequancy Polarization effects appear more scattered if we consider results on coda Also vertical SSRs highlight amplification for stations installed in the basin, even if at frequency slightly higher (1.5 Hz vs. 0.8 and 3.5 Hz vs. 2) Selecting a sub set not including LAquila events the low frequancy peak (0.8 Hz) is presenr again but it is characterized by low amplitude values The ananlyses computed by S-Transform highlight that the surface waves have a large contribution of Love wave (non torna con quello che dice GFZ) SEISMIC SITE EFFECTS IN NORCIA BASIN (CENTRAL ITALY)

18 Thank you for the attention ! 30° convegno nazionale GNGTS, Trieste, novembre 2011

19 Extra slides

20 HVSR for the reference stations (on S-phase)

21


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