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Seismic Characterization and Scenarios in Nice Region

This project aims to identify active faults, estimate kinematics and mechanics, and develop seismic scenarios for the Nice region. It includes seismo-tectonic investigations, waveform analysis, and study of deformation rates.

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Seismic Characterization and Scenarios in Nice Region

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  1. WP2 - Source characterization and Determination of earthquake scenarios WP-2-1: Seismo-tectonic investigationPI: Christophe Larroque, GEOAZUR and Oona Scotti, IRSNWP-2-2: Seismic source characteristicsPI: Martin Vallée, GEOAZUR Laboratories involved: GEOAZUR, IRSN, CEREGE QSHA WP2 Status report

  2. Long term objectives • Identification of potentially seismically active faults • Estimates of the kinematics (slip rate, if possible) and mechanics (fault plane solution) of the active faults • Identification of seismotectonic zones with « homogeneous seismic potential» • List of potential seismic scenarios to be used by ground motions modelers QSHA WP2 Status report

  3. Progress report ( June 2006) 13 janvier 2006: Meeting in Nice: L. Siame, O. Bellier +Géoazur 9 March 2006: Meeting in Paris: O. Scotti and C. Larroque 27 april 2006: Meeting in Nice: J. Angelier, N. Béthoux, B. Delouis, A. Deschamps, C. Larroque, M. Régnier, M. Vallée QSHA WP2 Status report

  4. WP2.1 Work plan • Seismic scénarios for the Nice region (2006/2007) • Seismotectonic investigations (2006-2008) • Regional studies of long/short term deformation rates (2006-2008) QSHA WP2 Status report

  5. WP2.1 1. Seismic scénarios for the Nice region QSHA WP2 Status report

  6. WP2.1.1 Seismic scénarios for the Nice region Actions proposed in 2006 Scénario 1: based on the magnitude, location and depth estimates deduced for the two most important historical seismic events (1887, 1564) .....................................................D. Baumont and O. Scotti Scénario 2:For the 1887 event, an attempt will be made to calculate the focal mechanisms .............stage M2R UNSA with C. Larroque, M. Ioualalen, O. Scotti Scénario 3: Based on the recent study of the Blausasc fault: ..............F. Courboulex, C. Larroque, A. Deschamps et C. Sansorny Scénario 4: Based on the future study of the « Var » fault ......................................................C. Larroque + B. Delouis QSHA WP2 Status report

  7. WP2.1.2 Seismotectonic investigationsActions proposed for the Nice region in 2006 Characterizing the source of recent moderate earthquakes (Magnitude, location, depth and where possible focal mechanism)...................................................... B. Delouis Application of a new inversion method to compute the present-day stress field – identification of the « active » fault plane through a comparison with the prevalent direction of the nearest « active » faults................................................B. Delouis, J. Angelier Study of the quaternary stress field through a systematic analysis of alluvial and conglomeratic plio-quaternary outcrops of the Var valley and at Cap d’Ail ......................Angelier, B. Delouis, C. Larroque Waveform analysis of moderate ligurian earthquakes..........WP2.2 QSHA WP2 Status report

  8. WP2.1.3 Regional long/short term deformation rate estimatesActions proposed in 2006 • Study of the relationship between • the plio-quaternary long term uplift of the Var valley • the present-day strike-slip nature of the « Var » fault • and the evidence for important extensive processes active up till the Pliocene L. Siame, JC Hyppolite, G. Clauzon, O. Bellier CEREGE B. Delouis, C. Larroque GEOAZUR QSHA WP2 Status report

  9. Deliverables WP2.1 • Draft of potential seismic scenarios for the city of Nice (M, distance and most likely fault plane solution) based on seismotectonic arguments.......................................2006 • Draft of potentially active faults with a description of their kinematics...................................................2007/2008 • Dating of terraces in the Var valley.........................2008 • Identify the driving mechanism of compressional and extensional processes ( role of gravity?)......................2008 QSHA WP2 Status report

  10. WP2.2 Work plan • Objectives for the three years • Depth • Focal mechanism • Source duration • of well instrumented events (M>3) of the last 10 years • in the region of Nice (Southern Alps) F. Courboulex, B. Delouis, M. Vallée, F Courboulex, A. Deschamps, M. Régnier, N. Béthoux QSHA WP2 Status report

  11. WP2.2.1 Hypocentral location techniques • Beuil earthquake (M=3.8 on 2005/12/20 at 23 :57 :32.591). • located (44.120°, 6.988°): • 3 seismological regional arrays (TGRS, SISMALP and DISTER (Italie)) • and two national arrays (RAP and RENASS). • good azimutal coverage. • 1D velocity model used for location procedure is chosen very simple. • Hypocentral location is found very stable, with RMS 0.2 sec • Depth: 0 and 2 km. • Five stations are located less than 20 km from epicenter • The shallowness of focal depth is confirmed by a conic wave • arriving first at close stations. QSHA WP2 Status report

  12. WP2.2.1 Deliverable 2006+ • estimate the range of likely focal depths as a function of the location and tectonic context of the earthquakes QSHA WP2 Status report

  13. WP2.2.2 (FM) Polarity analysis of direct and refracted P waves • stations between 10 and 150 km • very dependent on the velocity model (Moho depth for refracted waves) QSHA WP2 Status report

  14. WP2.2.2 (FM) Waveform-fitting- • few close stations (accelerometers or broad band stations) • model complete wavefield (near, intermediate and far-field) • less dependent on the assumed crustal structure than Polarity analysis QSHA WP2 Status report

  15. Deliverables WP2.2 2006+ • extend these methods to significant past earthquakes of the regions to better constrain the most likely seismic scenarios. • Polarity analysis method will also be used more specifically for recent earthquakes recorded by OBS, in order to get better information for simulation of an offshore earthquake close to Nice QSHA WP2 Status report

  16. WP2.2.3 Source duration Using the Empiral Green function (EGF) analysis QSHA WP2 Status report

  17. Deliverable WP2.2 2006+ • Objectif: Thanks to the good sensitivity of the local networks • find for most of the M>3 earthquakes one or several suitable EGFs • correlate the source duration of the earthquakes with their magnitude • confront with classical scaling laws • extrapolate towards bigger magnitudes, relevant for seismic scenarios • Correlate source duration and depth/focal mechanism QSHA WP2 Status report

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