Seismic Hazard Assessment Study for the Eastern Caribbean Islands

Transcription

1 Seismic Hazard Assessment Study for the Eastern Caribbean Islands Port of Spain, Trinidad May 2nd 2011 Walter Salazar Richard Robertson Lloyd Lynch Joan Latchman Elisa Zuccolo Francesca Bozzoni Mirko Corigliano Carlo Lai Laura Scandella

2 Outline The Studied Area Critical Review of the Past Seismic Hazard Assessment Studies Probabilistic Seismic Hazard Analysis (PSHA) Methods of calculation - Classical Cornell-McGuire approach - Zone-free approach by Woo (1996) Construction of the Earthquake Catalogue Identification of Seismic Zones Processing of the Catalogue Attenuation Relationships PSHA analysis and results Compatibility with IBC 2009/ASCE 7-05 Vertical component Influence of seismogenic zone Practical application 2

3 Probabilistic Seismic Hazard Analysis (PSHA) Identification of seismogenic zones (Cornell-McGuire approach) 3

4 Definition of Seismogenic Sources WE NEED TO SEPARATE THE EVENTS LISTED IN THE CATALOGUE IN SEISMOGENIC ZONES ACCORDING TO THE TECTONIC-GEOLOGICAL INFORMATION

5 Used instruments In-depth investigation of the scientific publications regarding the seismotectonic setting of the Eastern Caribbean region Analysis of transversal sections Compatibility analyses between the proposed seismic delimitation and the Catalogue events using ArcGIS 5

6 Seismogenic sources Proposed geometric delimitation Zone 1: Volcanic Island-arc. Zone 2-5: Subduction in the Lesser- Antilles. Zones 6-8: Puerto Rico and Virgin Islands. Transition Zones 9 and 10A. Zone 10B: East of Trinidad. Zone 11: North of Paria Peninsula. Zone 12: Trinidad Faults. Zones 13 and 14: El Pilar fault. Zone 15: South of Trinidad. 6

7 Zone 1: Volcanic Island-arc. Zone 1 covers the area from north of Martinique to Anguilla, including the Leeward Islands. These islands are volcanic in origin. The strong (maximum historical magnitude of about 6.6 M W occurred in 1897) shallow earthquakes typical of this zone are not necessarily associated with volcanic eruptions and frequently occur in clusters with no discernible mainshock (swarms). 7

8 Zone 1: Volcanic Island-arc. Seismicity is concentrated within the uppermost 35 km of the Caribbean plate in the Lesser Antilles; the epicenters are concentrated in a nearly continuous belt 100 km wide, which develops along both the axis of the principal active volcanoes and the inland and offshore shallow faults which run parallel to the Subduction Trench. The fault plane solutions in this zone yield both normal and strike-slip focal mechanisms. 8

9 McCann (1985): - position of Volcanic Arc - dimension of Volcanic Arc; 9

10 Zone 2-5: Subduction in the Lesser-Antilles. The volcanic island-arc lies about 300 km from the Eastern Caribbean Trench, where the North American plate begins to subduct beneath the Caribbean plate, reaching depths of 200 km below the islands and generating large earthquakes of magnitude up to 8.0 M W. SZ2 and SZ3 include all the shallow focus earthquakes (depth 50 km) along the inclined inter-face seismic zone that yields underthrust focal mechanisms (Byrne et al., 1988). Convergence between the Caribbean and North American plates occurs at a rate of about 37 mm/yr (Sykes et al., 1982; McCann, 1985). 10

11 (Byrne, Davis and Sykes, 1988) Interface and Intraplate subduction and Volcanic island arc seismicity (McCann, 1985) 11

12 Upper Crustal seismicity and inter and intra-plate subduction seismicity Transversal Trasversal section USGS/PDE ( ) Long (km) Dep (km) (12-14 N) 12

13 Zone 2-5: Subduction in the Lesser-Antilles. Focal mechanisms of deeper intra-plate events (>50 km) indicate that normal faulting is due to the initial flexure of the downgoing Atlantic slab (SZ4 and SZ5) with an average westward dipping of 50 degrees (Bengoubou-Valeruis et al., 2008). SZ2 and SZ3 have been distinguished as well as SZ4 and SZ5, since SZ2 and SZ4 are characterized by a higher seismic activity if compared with SZ3 and SZ5. 13

14 14

15 Bengoubou-Valeruis et al. (2008) and Russo et al. (1993) attributed the different seismic activity to the following reasons: - changes in the tectonic structures mapped by Feuillet et al. (2002); - sediment volume sufficient to lubricate or decouple the two plates in the subduction zone; - strengthening caused by thick accretionary prism overburden which lies above the shallow reach of the subduction zone; the quiescent area coincides with the deepest part of the Barbados accretionary wedge. SZ2 and SZ3 partially overlap SZ4 and SZ5 respectively and SZ4 is partially overlapped by SZ1 15

16 SZ2 and SZ3 partially overlap SZ4 and SZ5 respectively and SZ4 is partially overlapped by SZ1 16

17 Zones 6-8: Puerto Rico and Virgin Islands. Clinton et al. (1996) 17

18 Zones 6-8: Puerto Rico and Virgin Islands. The Puerto Rico and the Virgin Islands area is considered a microplate surrounded by the obliquely subducting North America plate, the Caribbean plate and several major faults - the Mona Canyon to the East, the Abnegada Passage to the West (McCann, 1985, Jansma et al., 2000) and the Muertos Trough to the South. This region has been considered in a simplified way since the seismic hazard assessment of this area is outside the scope of this study. 18

19 (Z8) The absence of (Z6) volcanism in Puerto Rico and the Virgin Islands suggests that this zone is not an extension of the island-arc Lesser Antilles structure (Molnar & (Z7) Sykes, 1969). (Z7) 19

20 Zones 6-8: Puerto Rico and Virgin Islands. SZ6 includes the Puerto Rico Trench area down to a depth of 50 km. SZ7 comprises shallow faults (depth < 50 km) in the inland of Puerto Rico and offshore. SZ8 includes the intra-plate subduction seismicity generated by the bending of the North-American slab, with depth 50 km. A recent research suggests the existence of the subducted Caribbean slab confirmed by low velocity anomalies beneath the Island (Mendoza and McCann, 2009), thus this seismogenic area comprises both the subducting North America and Caribbean slabs, dipping southward and northward, respectively, beneath the microplate. SZ6 and SZ7 overlap SZ8. 20

21 Crustal seismicity, interface and intraplate seismicity Transversal Trasversal section (17-18 N) USGS/PDE ( ) Long (km) Dep (km)

22 Transition Zones 9 and 10A. Normal Faulting Right Lateral 22

23 Transition Zones 9 and 10A. These seismogenic zones represent the intersections between the transform faults and subduction zones, and the Lesser Antilles Arc located at the north and at the south of the Eastern Caribbean. SZ10A includes the shallow seismic activity in the southern part of the island of Tobago which is considered within the Caribbean- South American plate boundary (Latchman, 2009; and Burmester et al., 1996). SZ9 is located at the boundary between the Lesser Antilles arc and the Puerto Rico Trench. It is characterized by a low level of seismicity and it mainly generates normal focal mechanism earthquakes. 23

24 Zone 10B: East of Trinidad. 24

25 Zone 10B: East of Trinidad. Earthquakes located in this zone are consistent with the detachment and bending-flexure of the South American slab which moves toward the collision zone (Russo and Speed, 1992). The zone is mainly characterized by normal faulting mechanism with ENE/WSW striking planes and strike slip faults with an average depth of 45 km. 25

26 Zone 11: North of Paria Peninsula (Russo et al., 1993) 26

27 Crustal seismicity and intra-plate seismicity Dep (km) Transversal section Trasversal section USGS/PDE ( ) Long (km) (10-11 N) 27

28 Zone 11: North of Paria Peninsula This zone constitutes a subducting detached oceanic lithosphere with depth ranging from 50 to 300 km and represents one of the most active seismogenic sources in the Eastern Caribbean (Russo et al. 1993; SRC, 2009). The focal mechanisms suggest that normal faulting from the initial flexure of the down going slab with a steeply NW-dipping of 60 degrees is occurring. However, mixed-motion earthquakes with thrust and strike slip support the interpretation that there is bending of the subducting slab at greater depths. 28

29 Zone 12: Trinidad Faults. Weber et al (2009) 29

30 Zone 12: Trinidad Faults. This zone includes the faults mapped in Trinidad namely, the Northern-Range, Central Range, Darien Ridge, Arima and Los Bajos Fault, characterized by earthquake with depth < 50 km (SRC, 2009, Algar and Pindell, 1993). 30

31 Zones 13 and14: El Pilar fault. 31

32 Zones 13 and 14: El Pilar fault. These zones comprise the eastern boundary between the Caribbean and the South American plates. Earthquakes located within the El Pilar fault near the northern coast of South America are shallow events, with depth < 50 km and mainly characterized by right lateral strike slip mechanisms. The Caribbean plate is moving at about 20 mm/yr in an easterly direction relative to South America (Pérez et al., 2001). However, thrust focal mechanism events also take place in this region reflecting the oblique collision at crustal levels between the Caribbean and the South American plates. A high level of seismicity characterizes SZ13, while a moderate seismicity level characterizes SZ14. 32

33 Zone 15: South of Trinidad. Russo et al. (1993) defined this zone as a passive margin in the northern South America. It includes events with strike-slip, mixed thrust and strike-slip and thrust mechanisms around the Orinoco-Delta region in Venezuela, with an average depth of 50 km. 33

34 Main characteristics of the seismic zones Depth (km) Type Main Focal Mechanism ZONE Upper-crustal Normal and Strike-Slip ZONE Interface Thrust (Inverse) ZONE Interface Thrust (Inverse) ZONE Intraplate Normal ZONE Intraplate Normal ZONE Interface Thrust and Strike-Slip ZONE Shallow Normal ZONE Intraplate Normal ZONE Transition Normal and Strike-Slip ZONE Transition/Intraplate Normal and Strike-Slip ZONE Intraplate Normal ZONE Crustal Normal and Strike-Slip ZONE Crustal Strike slip and Thrust ZONE Crustal Strike slip and Thrust ZONE Crustal Strike slip and Thrust 34

35 log(lmw) Gutenberg-Richter recurrence relationships The magnitude range of amplitude is assumed equal to 0.5 for all zone except for ZONE 1, for which this value is ZONE 1 y = x R 2 = M W zone a b M min M min a b n M min M max1 M max2 EI (M min ) EI (M max1 ) EI (M max2 )

36 Seismogenic sources with events 36

37 Ground Motion Prediction Equations (GMPEs) 37

38 GROUND MOTION PREDICTION EQUATIONS (GMPEs) Log y = a + b M + c log R + d R + s + sigma SOURCE PATH SITE y : ACCELERATION, M: MAGNITUDE, R: DISTANCE a,b,c,d,s and sigma: regression analysis 38

39 Rodriguez (2003) 39

40 Analyzed GMPEs SUBDUCTION ZONES: Youngs et al. (1997) Atkinson and Boore ( ) Zhao et al. (2006) Kanno et al. (2006) Lin and Lee (2008) CRUSTAL ZONES: Kanno et al. (2006) Zhao et al. (2006) Abrahamson and Silva (2008) Boore and Atkinson (2008) Campbel and Bozogornia (2008) Chiou and Youngs (2008) VOLCANIC ZONE: Sadigh et al. (1997) Salazar (2004) El Salvador Zhao et al. (2006) Kanno et al. (2006) McVerry et al. (2006) New Zealand Abrahamson and Silva (2008) Chiou and Youngs (2008) 40

41 We corrected about 1,000 acceleration time histories using a base-line correction, a band pass filter and perform the integration in the frequency domain yielding the velocity and displacement postscript plots. The correspondent Fourier and Response Spectra for 5% damping are also reproduced in this scheme. 41

42 Comparison of GMPEs with available data Seismic Research Centre (SRC) BRGM (Bureau de Recherches Géologiques et Minières - France) Date M w H Earthquake type Lat. Long. November 29, intraplate October 4, intraplate October 28, intraplate November 15, intraplate October 24, intraplate November 17, intraplate January 25, intraplate June 8, interface December 2, crustal December 3, crustal June 21, crustal November 21, Volcanic island arc

43 Acceleration (g) (g) Acceleration (g) (g) Acceleration (g) Acceleration (g) (g) Comparison of GMPEs with available data Mw =6.1 T =0 sec 10 0 Mw =6.1 T =0 sec Mw =6.1 T =0 sec Mw =6.1 T =0.2 sec Mw =6.1 T =0.2 Mw sec=6.1 T =0.2 sec Hypocentral 10 2 distance (km) Hypocentral distance Hypocentral (km) distance (km) Mw =6.1 T =1 sec 10 0 Mw =6.1 T =1 sec Mw =6.1 T =1 sec Hypocentral 10 2 distance (km) Hypocentral distance Hypocentral (km) distance (km) Hypocentral 10 2 distance (km) Hypocentral Youngs et al. distance 97 Hypocentral - average (km) distance (km) " average + Youngs et al. 97 Youngs - average et al average " - average average - " + - average + Kanno et al., 06 average " - average " - - average - average + Kanno et al., 06 Kanno - average et al., 06 - average " - average average - " + - average + Lin & Lee 08 - average " - average " - - average - average + Lin & Lee 08 Lin - average & Lee 08 - average " - average average - " + - average + Zhao et al. 06 average " - average " - - average - average + Zhao et al. 06 Zhao - average et al average " - average average - " + - average + Atkinson & Boore 08 - average " - average " - - average - average + Atkinson & Boore 08 Atkinson - average & Boore 08 - average average - " - average " + - average component=1 station=tptc " - average " - - average component=2 station=tptc component= station=tptc component=1 station=tptc component=1 station=tbh component= station=tptc component=2 station=tptc component=2 station=tbh component= station=tbh component=1 station=tbh component= station=tbh component=2 station=tbh INTRAPLATE EVENT October 4,

44 Acceleration (g) (g) Acceleration (g) (g) Acceleration (g) Acceleration (g) (g) Comparison Mw =5.8 T =0 sec of GMPEs with available data 10 0 Mw =5.8 T =0 sec 10 0 Mw =5.8 T =0 sec Hypocentral distance (km) Hypocentral 10 2 distance (km) Hypocentral distance (km) Mw =5.8 T =1 sec Mw =5.8 T =1 sec Mw =5.8 T =1 sec Hypocentral distance (km) 10 2 Hypocentral 10 2 distance (km) Hypocentral distance (km) Mw =5.8 T =0.2 sec 10 0 Mw =5.8 T =0.2 sec Mw =5.8 T =0.2 sec Hypocentral distance (km) Hypocentral 10 2 distance (km) Youngs et al average Youngs et al. 97 Hypocentral - average distance (km) " - average + " - average " average + Youngs - et al average Kanno et al., 06 - average " - average average + - " - average Kanno + et " al., 06 - average average - " - average " average + Kanno - et al., 06 - average Lin & Lee 08 - average " - average average + - " - average Lin & Lee + 08 " - average - " - average " - average + Lin & Lee average Zhao et al average " - average average + - " - average Zhao et + al. 06 average " - average - " - average " average + Zhao et - al average Atkinson & Boore 08 - average average - " - average + " - average Atkinson + & Boore 08 - average " - average - " - average " - average + Atkinson - & Boore 08 - average component=1 station=mbra average - " - average component= station=mbra component=1 station=mbra " - average component= component=2 station=mbra station=gbra component=1 station=mbra component= component=1 station=gbra station=gbra component=2 station=mbra component= component=2 station=gbra station=gpaa component=1 station=gbra component= component=1 station=gpaa station=gpaa component=2 station=gbra component=2 station=gpaa component=1 station=gpaa component=2 station=gpaa - INTERFACE average EVENT June 8,

45 Acceleration (g) Comparison of GMPEs with available data 10 0 M w =6.3 T =0 sec Hypocentral distance (km) Sadigh et al., 97 - average " - average + " - average - Zhao et al average " - average + " - average - Kanno et al., 06 - average " - average + " - average - Abrahamson & Silva 08 - average " - average + " - average - Chiou & Youngs 08 - average " - average + " - average - Salazar, 04 - average " - average + " - average - McVerry et al., 06 - average " - average + " - average PGA from Bengoubou-Valerius et al. 08 VOLCANIC ARC EVENT November 21,

46 Cornell-Mc-Guire method: Adopted GMPEs SUBDUCTION ZONES: Youngs et al. (1997) Atkinson and Boore ( ) Zhao et al. (2006) Kanno et al. (2006) Lin and Lee (2008) CRUSTAL ZONES: Kanno et al. (2006) Zhao et al. (2006) Abrahamson and Silva (2008) Boore and Atkinson (2008) Campbel and Bozogornia (2008) VOLCANIC ZONE: Sadigh et al. (1997) Zhao et al. (2006) Kanno et al. (2006) Abrahamson and Silva (2008) Chiou and Youngs (2008) Zone-free approach: Zhao et al. (2006), Kanno et al. (2006) 46

47 PSHA analysis and results 47

48 RESULTS Influence of seismogenic zones 48

49 -92,16-92, , ,13 SOFTWARE VALIDATION LOG N = M LOG Y = M-LOGR R SIGMA = M MIN = 4.0 AND M MAX = 8.2 Peak Ground Acceleration (cm/s/s) FZ RISK -85.5,10 Number of earthquakes / year OUR PROGRAM - SRC Number of earthquakes / year

50 Annual Frequency of Exceedance Island of Dominica 1/475 = 2.1E-03 1/2475 = 4.0E E E E E E E E E E E-07 Dominica T=0s Acceleration (g) SZ01 SZ02 SZ03 SZ04 SZ05 SZ06 SZ07 SZ08 SZ09 SZ10 SZ11 SZ12 SZ13 SZ14 SZ15 ALL RP=2475 y RP=475 y Cornell-McGuire approach Hazard dominated by Zone 4 Intra plate and Zone 1 Volcanic island-arc 50

51 SA (g) Island of Dominica Cornell-McGuire approach Hazard dominated by Zone 4 and Zone Dominica RP=2475 years T(s) SZ01 SZ02 SZ03 SZ04 SZ05 SZ06 SZ07 SZ08 SZ09 SZ10 SZ11 SZ12 SZ13 SZ14 SZ15 ALL 51

52 Annual Frequency of Exceedance Island of Dominica 1/475 = 2.1E-03 1/2475 = 4.0E-04 Zone-free approach - GMPE Zhao etal. (2006) Hazard dominated by deep and shallow seismicity Dominica T=0s 1.00E E E E-02 Deep Shallow Total RP=2475 y RP=475 y 1.00E E E E E Acceleration (g)

53 Annual Frequency of Exceedance Island of Dominica Zone-free approach - GMPE Kanno etal. (2006) Hazard dominated by deep and shallow seismicity 1/475 = 2.1E-03 1/2475 = 4.0E-04 Dominica T=0s 1.00E E E E-02 Deep Shallow Total RP=2475 y RP=475 y 1.00E E E E E Acceleration (g) 53

54 RP=95 years (10% in 10 years) Seismic Hazard maps PGA (g) 0.2s SA (g) 1s SA (g) Resolution: every degress = 2.8 km 54

55 RP=475 years (10% in 50 years) Seismic Hazard maps PGA (g) 0.2s SA (g) 1s SA (g) 55

56 Seismic Hazard maps RP=975 years (10% in 100 years) PGA (g) 0.2s SA (g) 1s SA (g) 56 56

57 RP=2475 years (2% in 50 years) Seismic Hazard maps PGA (g) 0.2s SA (g) 1s SA (g) 57 57

58 Conclusion - The complex tectonics of the Eastern Caribbean suggests a detail seismogenic sources delimitation to be incorporated in the hazard assessment, which is dominated by intra-plate seismicity in most of the islands with an important contribution of the uppercrustal earthquakes located in the volcanic arc as well. - The installation of a new strong motion network is a must to develop GMPEs for the Eastern Caribbean. 58

59 Practical Examples Get the design response spectra and the seismic coefficients Cs for the following site: a) Scarborough -Tobago (Hotel 20 stories) 59

60 Tobago Hotel 60

61 1.85 g 61

62 0.375 g 62

63 Sa S S 1.23g a T DS The Seismic Coefficient Cs Fundamental Period: T = 2.0 s (after dynamic analysis) S a SD1 0.25g T T Cs = 0.13g Reduction factor R= g 0.04s 0.20s Cs = 0.13g/8=0.016g 63

64 SAP/ETABS MODEL 64

65 This work will be published in the Journal of the Seismological Society of America MUCHAS GRACIAS!! 65