Réunion PARIS 29/06/2006 QSHA WP2 Status report 1 WP2 - Source characterization and Determination...

QSHA WP2 Status report

1Réunion PARIS 29/06/2006

WP2 - Source characterization and Determination of earthquake scenarios

WP-2-1: Seismo-tectonic investigation

PI: Christophe Larroque, GEOAZUR and Oona Scotti, IRSN

WP-2-2: Seismic source characteristics

PI: Martin Vallée, GEOAZUR

Laboratories involved: GEOAZUR, IRSN, CEREGE



• 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

Long term objectives



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



WP2.1 Work plan

1. Seismic scénarios for the Nice region (2006/2007)

2. Seismotectonic investigations (2006-2008)

3. Regional studies of long/short term deformation rates (2006-2008)



WP2.1 1. Seismic scénarios for the Nice region



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



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



WP2.1.3 Regional long/short term deformation rate estimates

Actions proposed in 2006

Study of the relationship between

1. the plio-quaternary long term uplift of the Var valley

2. the present-day strike-slip nature of the « Var » fault

3. 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



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



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



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.



WP2.2.1 Deliverable 2006+

estimate the range of likely focal depths as a function of the

location and tectonic context of the earthquakes



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)



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



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



WP2.2.3 Source duration

Using the Empiral Green function (EGF) analysis



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

Réunion PARIS 29/06/2006 QSHA WP2 Status report 1 WP2 - Source characterization and Determination...

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