Seismic microzonation of the Accumoli municipality (Rieti, Italy) after the August 24 th earthquake: preliminary considerations.

Transcription

1 Seismic microzonation of the Accumoli municipality (Rieti, Italy) after the August 24 th earthquake: preliminary considerations. C. Comina, M. Della Seta, C. Esposito, L. Falconi, S. Foti, L. M. Giannini, S. Hailemikael, L. Lenti, G. Martini, S. Martino, A. Paciello, F. Passeri, M. Proposito, C. Puglisi, S. Rivellino, Romeo R.W., L. Sambuelli, G. Scarascia Mugnozza, L. V. Socco, F. Troiani, C. Varone, V. Verrubbi

2 Study area: Macroarea2 Accumoli and villages - The study area is located less then 10 km far from to the epicenter of the 24 th August 2016 earthquake (M w 6.0) - It is located in the Latium Region and in the Rieti administrative zone - According to ISTAT the area includes 16 administrative villages and 682 inhabitants (ISTAT, 2013) - It is extended from the Mts of Laga to the Mts Sibillini, including part of the Tronto River valley at elevations varying from 700 up to 1750 m a.s.l.. Page 2

3 Geological setting: general view Cherty limestone group Marne a Fucoidi Scaglia Rossa Scaglia Cinerea Bisciaro MESO-CENOZOIC CARBONATIC DOMAIN Valle Tronto (lower zone) Grisciano 2 - Tino 3 - Illica 4 - Accumoli 5 - Fonte del Campo 6 - Poggio Casoli 7 - Villanova 8 - S.Giovanni 9 - Terracino Carbonatic ridge zone Valle Tronto (high zone) 3 Pre-evaporitic members: - arenaceous - arenaceous-pelitic - pelitic arenaceous CENOZOIC LAGA FLYSCH ZONE Marne con Cerrogna Marne a Pteropodi Flysch ridge zone Page 3

4 Geological setting: Tronto River valley (lower zone) - Alluvial fan deposits overlying or interlayered with coarse-size alluvial deposits - «V-shape» valley Page 4

5 Geomorphological features: Tronto River valley (lower zone) - Different generations of alluvial fan deposits overlying and interlayered each other - Heterogeneity of alluvial deposits due to fans overlying alluvia Page 5

6 Geophysical investigations: Tronto River valley (lower zone) Page 6

7 Geophysical investigations: Tronto River valley (lower zone) SARA SL06 Page 7

8 Geophysical investigations: Tronto River valley (lower zone) Page 8

9 Geophysical investigations: Tronto River valley (lower zone) GRI1 GRI3 GRI3 GRI2 GRI1 GRI2 Page 9

10 Geophysical investigations: Tronto River valley (lower zone) A Manual picking and seismic tomography are obtained by the commercial software RAYFRACT. B A Distance (m) GRI1 Possible water table D D C C B GRI2 Page 10

11 Geophysical investigations: Tronto River valley (lower zone) The inversion performed by the first resonance mode does not fit completely the low frequency behavior higher modes are probably requested to obtain a better fitting Vs 30 evaluation is very well constrained and the distribution obtained for the 24 equivalent models shows a central value at 350 m/s. Page 11

12 Geophysical investigations: Tronto River valley (lower zone) A A Manual picking and seismic tomography are obtained by the commercial software RAYFRACT. B Strada di accesso GRI3 GRI3 B Vs 30 evaluation is very well constrained and the distribution obtained for the 136 equivalent models shows a central value at 520 m/s. Page 12

13 Geological setting: Tronto River valley (upper zone) - Alluvial fan deposits overlaying and interlayered with coarse-grained alluvial deposits - «V shape» valley - Alluvial deposits at river confluence - Ridges with normally oriented slopes Page 13

14 Geomorphological features: Tronto River valley (upper zone) - Different generations of alluvial fan deposits overlyed and interlayered each other - Heterogeneity of alluvial deposits due to fans overlying alluvial deposits Page 14

15 Geophysical investigations: Tronto River valley (upper zone) Page 15

16 Geophysical investigations: Tronto River valley (upper zone) Page 16

17 Geophysical investigations: Tronto River valley (upper zone) Page 17

18 Geophysical investigations: Tronto River valley (upper zone) FCAMP Page 18

19 Geophysical investigations: Tronto River valley (upper zone) falda Manual picking and seismic tomography are obtained by the commercial software RAYFRACT. bedrock FCAMP The dispersion curves were obtained by merging MASW, REMI and circular arrays. The circular array data were processed by the fkbeamforming approach. Also in this case the fitting will be improved by considering upper modes and not only the first one. Vs 30 evaluation is very well constrained and the distribution obtained for the 278 equivalent models shows a central value at 530 m/s. Page 19

20 Geophysical investigations: Tronto River valley (upper zone) Preliminary results in terms of HVSR from the recorded weak motions show a significant amplification in the 5-7Hz frequency range, ascribable to the resonance of alluvial deposits Page 20

21 Geophysical investigations: Tronto River valley (upper zone) Page 21

22 Geophysical investigations: Tronto River valley (upper zone) Page 22

23 Geological setting: carbonatic ridge zone - Debris cover overlying a stiff bedrock - Cataclastic belt along the thrust zone - Different jointing conditions of the outcropping rock masses Page 23

24 Geomechanical characterization: carbonatic ridge zone Meso-cenozoic carbonatic domain Cenozoic emipelagic domain Villanova village Page 24

25 Geomechanical characterization: carbonatic ridge zone Page 25

26 Geophysical investigations: carbonatic ridge zone Villanova S.Giovanni Terracino Page 26

27 Geological setting: flysch ridge zone Cassino - Narrow ridges in the arenaceous and pelitic members of the Laga Flysch, elongated almost NE- SW and EW Collespada Colleposta Page 27

28 Geological setting: flysch ridge zone 24 August 2016 Page 28

29 Already existing MOPS (I SM level) map More detail is requested to describe the intense jointing of the cataclastic belt along the thrust zone More details is requested to describe the geometrical setting among different alluvial deposits More detailed mapping of debris and weathered covers is requested More details is requested to describe the geometrical setting among different alluvial deposits Topographic features responsible for possible topographic amplification effects should be mapped Page 29

30 Slope Instabilities: PARSIFAL approach to III level SM PARSIFAL (Probabilistic Approach for Rating Seismically Induced slope FAiLures), is a comprehensive approach aiming at quantifying the hazard related to earthquakeinduced landslide at municipality as well as at regional scale Ongoing activities ismica.it/it/attivita/terremotocentro-italia/49-applicazione-dellapproccio-parsifal-nell-areacolpita-dal-sisma-del-24-agosto Page 30

31 - Detection of areas without wood cover - Detection of main connection lines (roads, tracks.) - Use of buffers to allow stability analysis of man-made trenches along roads Slope analysis: preliminary results Page 31

32 Geomechanical survey of jointed rock masses - Geomechanical survey of jointed rock masses, prelimirary to rock mass zonation and kinematic tests for evaluating the suitability of different failure mechanisms Page 32

33 Slope analysis: preliminary results - Half-basin morphometry analysis for carrying on slope stability for first time shallow landslides - Geomechanical survey to perform a lithotecnical zoning of debris and weathered covers Page 33

34 Inventorying of already existing landslides - Use of the LIDAR DEM available from CNR for the Maroarea2 territory - Landslide inventorying from IFFI+PAI+MS1 (where existing) and validation of the mapping criteria - Design of a geodatabase for already existing landslides Page 34

35 Geomechanical survey of already existing landslides Page 35

36 Timeschedule and State of Art Page 36

37 Macroarea2 Accumoli and villages: preliminary conclusions - The Macroarea2 zone is characterized by local seismic amplification, mainly related to the alluvial deposits of the Tronto river valley - Minor amplification effects are measured somewhere in debris due to weathered rock masses, landslides or taluses - Topographic amplification effects can be supposed up to now even if numerical and instrumental data are still necessary to demonstrate and better constrain them - Both 1D and 2D conceptual models for local seismic response can be considered in the Macroarea2 zone; these models will represent the start-point for planning boreholes and DH tests as well as numerical modelling Page 37

38 Thanks for your attention GeoslopestabSPZ Geo-slopestability "Sapienza" Pagina 38