Earthquakes of and successive. A. Caporali and L. Ostini Department of Geosciences University of Padova 2012 EUREF Symposium, Paris France

Transcription

1 Earthquakes of and successive A. Caporali and L. Ostini Department of Geosciences University of Padova 22 EUREF Symposium, Paris France

2 Historical Seismicity: 234 M 5.8 +/-.2 near Ferrara 57 M 5.5 Ferrara 99 M 5.5 Lower Po plain

3 Tectonic setting Two concurrent active processes: counterclockwise rotation of the Apennines related to the opening of the Thyrrenian sea Northwards convergence of the Adria microplate towards the stable European foreland

4 Pressure and Tension axes of the Fault Plane Solution indicate a reverse faulting: coherent with structural setting

5 Time series of permanent GPS stations vertical lines in the time series indicate occurrence of seismic event LEGN (Legnago) MODE (Modena) SGIP (San Giovanni Persiceto)

6 Table of displacements as a function of distance from epicenter of the event Longitudine Latitudine Delta Est (m) Delta Nord (m) DeltaVerticale (m) distanza da epicentro Stazione SGIP SBPO LEGN MODE BTAC LDNS ROVI TEOL VR VICE CGIA epicentro

7 Table of displacements as a function of distance from epicenter of the event Longitudine Latitudine Delta Est [m] Delta Nort [m] Delta Verticale [m] Distanza da epicentro (km) Stazione LEGN LDNS BTAC SGIP MODE VR ROVI TEOL VICE CGIA epicentro

8 Latitude (degree) For both events Rupture area 2x8 km Updip slip.25.3 m m 44.2 (constrained to keep the seismic moment) Dip angle ca 3 deg Depth km Use GPS to adjust coordinates of epicenter Longitude (degree) Coulomb Jun-22 22:9: _gps.inp Map view grid Depth:. km

9 Modeling surface displacement in terms of elastic dislocation at depth U a d W 3 N u E d 2 d L h d d Single rectangular fault 2 x 8 km, ca 8 km deep A constant dislocation of 35 cm along the fault plane in reverse direction generates the observed pattern of GPS displacements at the surface

10 Y (km) Y (km) Y (km) Apriori model from seismology (left); improved model with GPS data (center); difference (right): how to make seismology and GPS working together event m -. m X (km) Coulomb May-22 5:29: _gfz.inp Map view grid Depth: 4.89 km 5 5 X (km) Coulomb May-22 5:27:4 2522_onlyGPS.inp Map view grid Depth: 4.89 km 5 5 X (km) Coulomb May-22 :: i Map view grid Depth: 4.89 k

11 Y (km) Expected vertical model (to be validated with DInSAR data) Vertical displacement (m) x -4 mm uplift expected: not large because fault is probably at low dip angle (3 deg) m 5 5 X (km) Coulomb May-22 6:8: _onlyGPS.inp Vertical displacement Depth:. km -8

12 Depth(km) In conclusion: what happened at depth? Displacement of ca. 35 cm updip, along a 3 deg south dipping plane LxW 2 x7 km, km depth of the center. On the 29.5 the fault and displacement were very similar. A Displacement projected onto cross section B m Distance(km) Coulomb May-22 6:5:7 2522_onlyGPS.inp A(93.75,-53.4) --- B(2.49,24.5)

13 Y (km) How much stress was transferred to Depends an assumed friction coefficient (.4) Could be of the order of a few bar (or few kpa) within few tens of km Sufficient to trigger the May 29 Mw=5.9 event? Could the events of the 2 and 29 jointly transfer to nearby faults sufficient stress to trigger additional events? Should we concentrate on reverse faults or consider also sinistral strike slip faults, which do exist in the area? Were the faults to the East of the May 2 fault unloaded? nearby faults? Load added at the fault of the May event? m Coulomb stress change (bar) 5 5 X (km) Sigma- Sigma-2 Sigma-3 Coulomb May-22 6:4: _onlyGPS.inp Opt. thrust faults Depth: - km Friction:

14 Westwards drift of the seismicity B B

15 Summary Event in a seismic region, among the highest intensity if not the most intense; large replica 9 days later: receiver fault activated by Coulomb stress transfer? GPS stations give crucial data within few hours (processing on Sunday!): fault plane solution can be better constrained with GPS data than with seismological data alone. Daily updates using IGS rapid orbits. Georeferencing coherent with Datum from Class A EPN stations No discontinuity observed in EPN stations. MEDI unreliable. Uplift model ready for DInSAR data: validation very important Good practice for readiness in case of future events