Trinidad and Tobago in the current hazard picture for the...
Transcript of Trinidad and Tobago in the current hazard picture for the...
The University of the West Indies Seismic Research Centre email: [email protected]
Walter Salazar
Lloyd Lynch
Joan Latchman
Richard Robertson
National Consultation on Earthquake Safety in Trinidad and Tobago
July 2010
Trinidad and Tobago in the current hazard picture for
the Eastern Caribbean
The University of the West Indies Seismic Research Centre email: [email protected]
Objectives
• To present the level of Seismic Hazard
in terms of earthquake shaking for the
Eastern Caribbean region and Trinidad
and Tobago
• To present a practical example of how
to use the new seismic hazard maps
The University of the West Indies Seismic Research Centre email: [email protected]
AGENDA
p.35, 34
• 1. Seismicity Evaluation
• 2. Strong Ground Motion Estimation
• 3. Probabilistic Seismic Hazard Assessment
• 4. Practical example
• 5. Conclusions
The University of the West Indies Seismic Research Centre email: [email protected]
Question
• Do you know the expected level of
earthquake shaking at your house or at
your work place in Trinidad ?
The University of the West Indies Seismic Research Centre email: [email protected]
• Where do earthquakes occur ?
• What is the size of the earthquakes ?
• How frequently do earthquakes occur ?
1. Seismicity Evaluation
The University of the West Indies Seismic Research Centre email: [email protected]
Where do earthquakes occur ? 15 Seismogenic zones
(Project collaboration with EUCENTRE-Italy)
The University of the West Indies Seismic Research Centre email: [email protected]
7
Main characteristics of the seismogenic zones
Depth (km) Type Main Focal Mechanism
ZONE 1 19.1 Upper-crustal Normal and Strike-Slip
ZONE 2 29.6 Interface Thrust (Inverse)
ZONE 3 29.4 Interface Thrust (Inverse)
ZONE 4 86.0 Intraplate Normal
ZONE 5 97.9 Intraplate Normal
ZONE 6 32.3 Interface Thrust and Strike-Slip
ZONE 7 28.4 Shallow Normal
ZONE 8 74.5 Intraplate Normal
ZONE 9 24.4 Transition Normal and Strike-Slip
ZONE 10 43.9 Transition/Intraplate Normal and Strike-Slip
ZONE 11 99.5 Intraplate Normal
ZONE 12 32.5 Crustal Normal and Strike-Slip
ZONE 13 23.3 Crustal Strike slip and Thrust
ZONE 14 14.7 Crustal Strike slip and Thrust
ZONE 15 57.3 Crustal Strike slip and Thrust
1
2
3
4
5
6
7
8
Seismic
Zones
that affect
T&T
The University of the West Indies Seismic Research Centre email: [email protected]
8
(Russo et al., 1993)
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, 2009b).
The University of the West Indies Seismic Research Centre email: [email protected]
9
(10-11 N)
Trasversal section
-250
-200
-150
-100
-50
0
-67 -65 -63 -61 -59 -57
Long (km)
Dep (km)
USGS/PDE (1973-2009)
Transversal section
Crustal seismicity
and intra-plate
seismicity
North of Paria
The University of the West Indies Seismic Research Centre email: [email protected]
How frequently do earthquakes occur ?
GUTENBERG-RICHTER
RECURRENCE RELATIONSHIPS
• LOG N = a + b * M
N: NUMBERS OF EARTHQUAKES
PER YEAR ABOVE
MAGNITUDE “M”
a: LEVEL OF ACTIVITY
b: is the measure of the relative abundance of large
to small shocks
ZONE 1
y = -1.0122x + 4.7943
R2 = 0.9882
-4.000
-3.500
-3.000
-2.500
-2.000
-1.500
-1.000
-0.500
0.000
0.500
4.5 5.0 5.5 6.0 6.5 7.0 7.5
MW
log
( lM
w)
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 11
• North of Paria Peninsula:
log N = 3.643 – 0.783 M
Recurrence interval* (T=1/N):
M=7.7: 243 years + 1766 = 2009
last big earthquake
M = 8.3 : 718 years
Log N = a + b M
Size of the earthquakes
*Recurrence interval: refers to the average time between earthquakes of a particular
magnitude or larger in a given seismic source
The University of the West Indies Seismic Research Centre email: [email protected]
12
Zones 13 and 14: El Pilar fault.
• These zones comprise the boundary
between the Caribbean and the
South American plate. The events
that have their origin in the fault are
shallow - less that 50 km depth - and
they are characterized mainly by right
lateral strike slip mechanism in the
northern coast of South America.
• We observed a high level seismic
output in Zone 13 that extends from
63.5º W to 62.3ºW longitude covering
the Araya-Paria Isthmus, and a
moderate seismicity level in Zone 14
that extends from 67.0º to 63.5º W
longitude covering the vicinity of
Caracas to the Araya region.
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 13
• El Pilar Fault:
log N = 3.392 -0.747 M
Recurrence interval (T=1/N):
M=7.2: 97 years
Log N = a + b M
The University of the West Indies Seismic Research Centre email: [email protected]
14
Right Lateral
Normal
Faulting
Transition Zone 10A.
• We define these seismogenic
zones as the intersection
amongst the transform faults
and subduction zones with the
Lesser Antilles Arc located at
the South of the Eastern
Caribbean.
• Zone 10A includes the shallow
seismic activity in the South
part of the island of Tobago
which we consider within the
Caribbean-South American
plate boundary (Latchman
2009, Weber, 2009 and
Burmester et al 1996). (Morgan
et al., 1988).
The University of the West Indies Seismic Research Centre email: [email protected]
15
Zone 10B: East of Trinidad.
• Russo & Speed (1992)
suggested that the
earthquakes located in this
zone are consistent with the
detachment and bending-
flexure of the South
American slab moving
toward the collision zone.
• The zone covers mainly
normal faulting mechanism
with ENE-WSW striking
planes and strike slip faults
with an average depth of 45
km.
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 10
• Transition zones and east of Trinidad:
log N = 2.127 – 0.531 M
Recurrence interval (T=1/N):
M=7.2: 50 years
Log N = a + b M
The University of the West Indies Seismic Research Centre email: [email protected]
17
Zone 12: Trinidad Faults.
Weber et al (2009)
• Weber (2001, 2009) affirms that the
N68ºE oblique trending in the Central
Range Fault is not associated with el
Pilar Fault 90º trending of pure
wrenching. The Central range fault
could be locked rather than creeping.
• The Northern Range and the Arima
Fault comprises a complex fault
system with lateral strike-slip, thrust
and normal faulting.
• Los Bajos Fault: south of Trinidad.
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 12
• Trinidad Faults:
log N = 2.580 – 0.664 M
Recurrence interval (T=1/N):
M=6.9: 100 years
Log N = a + b M
The University of the West Indies Seismic Research Centre email: [email protected]
19
Zone 2-5: Subduction in the Lesser-Antilles.
• We include in Zones 3 all the
shallow focus earthquakes
(depth ≤ 50 km) along the
inclined inter-face seismic
zone that yields underthrust
focal mechanisms (Byrne et
al. 1988).
• We include in Zone 5 deeper
intra-plate events (>50 km)
indicate that there is a normal
faulting resulting from initial
flexure of the down going
Atlantic slab with an average
of westward dipping angle of
50º (Bengoubou-Valeruis et
al, 2008).OLD SUBDUCTION
ZONE (100 m.y)
The University of the West Indies Seismic Research Centre email: [email protected]
20
(12-14 N)
Trasversal section
-250
-200
-150
-100
-50
0
-67 -65 -63 -61 -59 -57
Long (km)
Dep (km)
USGS/PDE (1973-2009)
Transversal section
Upper Crustal seismicity and
inter and intra-plate
subduction seismicity
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 3 (interface) and Zone 5 (intraplate):
• Subduction zones:
log N = 3.216 – 0.725 M Interface depth <= 50 km
log N = 2.941 – 0.680 M Intraplate depth > 50 km
Recurrence interval (T=1/N):
M=7.5: 167 years Interface
M=8.3: 505 years Intraplate
Log N = a + b M
The University of the West Indies Seismic Research Centre email: [email protected]
Zone 15: South of Trinidad.
• Russo et al. (1993) defined
this zone as a passive
margin edge in the Foreland
basin in North of South
America continent, covering
events with strike slip, mixed
thrust and strike slip, and
thrust mechanism around the
Orinoco-Delta region in
Venezuela, with an average
depth of 50 km and a
maximum magnitude of 6.6
(Mw).
The University of the West Indies Seismic Research Centre email: [email protected]
23
2. Strong Ground Motion Estimation
The strong motion is a potential destructive
movement of the ground that can produce a
significant damage or the collapse of building
structures in the near field.
The University of the West Indies Seismic Research Centre email: [email protected]
DATE MW H EARTHQUAKE TYPE
NOVEMBER 29, 2007 7.4 148.0 INTRAPLATE
OCTOBER 4, 2000 6.1 110.4 INTRAPLATE
OCTOBER 28, 2005 5.5 80.9 INTRAPLATE
NOVEMBER 15, 2006 5.2 98.9 INTRAPLATE
OCTOBER 24, 2005 5.1 137.7 INTRAPLATE
NOVEMBER 17, 2006 4.9 135.8 INTRAPLATE
JANUARY 25, 2001 4.6 85.5 INTRAPLATE
JUNE 8, 1999 5.8 52.4 INTERFACE
DECEMBER 2, 2004 5.8 48.2 CRUSTAL
DECEMBER 3, 2004 5.4 40.5 CRUSTAL
JUNE 21, 2003 5.3 10.0 SHALLOW
NOVEMBER 21, 2004 6.3 21.2 UPPER CRUSTAL
VOLCANIC ARC
24
• Seismic Research Centre (SRC)
• BRGM (Bureau de Recherches
Géologiques et Minières - France)
Compare available recordings of
acceleration with available Ground
Motion Prediction Equations (GMPEs)
-North of Paria Peninsula
-Trinidad Faults
-Transition zone
The University of the West Indies Seismic Research Centre email: [email protected]
25
3. SEISMIC HAZARD MAPS
Logic Tree Formulation
Zone and Free-Zone Methods
The University of the West Indies Seismic Research Centre email: [email protected]
HAZARD MAP 2475 YEARS RETURN PERIOD
PEAK GROUND ACCELERATION
Port of Spain
San Fernando
Point Fortin
HAZARD MAP 475 YEARS RETURN PERIOD
PEAK GROUND ACCELERATION
Port of Spain
San Fernando
Point Fortin
Rock conditions Rock conditions
(0.33g)
(0.28g)
(0.26g)
(0.58g)
(0.52g)
(0.48g)
The University of the West Indies Seismic Research Centre email: [email protected]
Gravity constant: g = 980.1 cm/s/s
Peak ground acceleration* = 0.58*980.1 = 569 cm/s/s
Acceleration: How fast the rate of shaking changes
In 1 second there is a change of 569 cm/s : 21 km/h
*Peak Ground Acceleration (PGA): The maximum recorded
acceleration value in a particular site during and earthquake
What does 0.58 g mean ?
The University of the West Indies Seismic Research Centre email: [email protected]
Peak Ground Acceleration 0.5 g Peak Ground Acceleration 0.3 g
Las Colinas
Curva La Leona
Salazar and Seo (2003)
El Salvador M=7.8 Jan. 13, 2001
The University of the West Indies Seismic Research Centre email: [email protected]
M=7.8
January 13, 2001
BOTH ARE INTRAPLATE SHOCKS
SAME DISTANCE (100 km) AND MAGNITUDE
7.8
What could happen if the earthquake occur
during the rainy season ?
El Salvador
Northern Range
Landslides in the photos
The University of the West Indies Seismic Research Centre email: [email protected]
Damaged house in Comasagua (La Libertad) with reinforced concrete frames
and reinforced brick walls – El Salvador Earthquake 2001.
Peak Ground Acceleration 0.6 g
The University of the West Indies Seismic Research Centre email: [email protected]
Peak Ground Acceleration 0.6 g
Collapsed ADOBE house in Santiago de María(Usulután)
El Salvador Earthquake 2001.
The University of the West Indies Seismic Research Centre email: [email protected]
• Return period: the mean (average) timebetween occurrences of a seismic hazard –for example, a certain ground motion at asite
• Recurrence interval: refers to the averagetime between earthquakes of a particularmagnitude or larger in a given seismicsource
• Life time (L): it refers to the effective life ofoccupancy of a building (generally 50 or 100years)
The University of the West Indies Seismic Research Centre email: [email protected]
34
Seismic Hazard maps
RP=95 years (10% in 10 years)
PGA (g) 0.2s SA (g) 1s SA (g)
Resolution: every 0.025 degress = 2.8 km
The University of the West Indies Seismic Research Centre email: [email protected]
35
RP=475 years (10% in 50 years)
PGA (g) 0.2s SA (g) 1s SA (g)
Seismic Hazard maps
The University of the West Indies Seismic Research Centre email: [email protected]
36
RP=975 years (10% in 100 years)
PGA (g) 0.2s SA (g) 1s SA (g)
Seismic Hazard maps
The University of the West Indies Seismic Research Centre email: [email protected]
37
RP=2475 years (2% in 50 years)
PGA (g) 0.2s SA (g) 1s SA (g)
Seismic Hazard maps
The University of the West Indies Seismic Research Centre email: [email protected]
0.2s
Spectral values
to be read in
the seismic
hazard maps
DESIGN RESPONSE SPECTRUM
Mapped Acceleration ParametersSs: is the acceleration for 0.2 s 5% damping
S1: is the acceleration for 1.0 s 5% damping
Ss
S1
The University of the West Indies Seismic Research Centre email: [email protected]
Why the hazard maps are
presented in terms of gravity “g”
• EARTHQUAKE INERTIA FORCES: F = m * a
m: mass of the building; m = W/g
a : acceleration
Engineers use Weight “W” for structural calculations:
If W = 130 ton and a=0.4 g
F= m * a = (130 ton/g) * 0.4 g = 52 ton.
The University of the West Indies Seismic Research Centre email: [email protected]
RP=2475 years (2% in 50 years)
1s SA (g)
Port of Spain
San Fernando
Point Fortin
North of Paria Peninsula
The University of the West Indies Seismic Research Centre email: [email protected]
41
4. PRACTICAL EXAMPLE
The University of the West Indies Seismic Research Centre email: [email protected]
42
Practical Example
• Get the design response spectrum and the
seismic coefficients Cs for the following
site:
Scarborough -Tobago (Hotel – 20 stories)
LIFE TIME = 50 YEARS AND
PROBABILITY OF EXCEEDANCE 2% :
2475 YEARS RETURN PERIOD
The University of the West Indies Seismic Research Centre email: [email protected]
44
Design spectral acceleration parameters IBC – ASCE 7_05
• SDS = 2/3*Fa * Ss
• SD1 = 2/3*Fv * S1
Fa and Fv: depends on soil conditions
For rock site conditions – CLASS B
It Corresponds to a shear wave velocity Vs = 760 m/s:
Fa = 1.0 and Fv = 1.0
Spectral acceleration for 1.0 s
Seismic
Hazard
maps
Spectral acceleration for 0.2 s
The University of the West Indies Seismic Research Centre email: [email protected]
47
The Seismic Coefficient Cs
Fundamental Period:
T = 0.1 n = 0.1 (20 ) = 2.0 s
n: number of stories
Fundamental Period T = 2.0 s
Cs = 0.13g
Reduction factor Ductility
and Overstrengh R= 8.0
Cs = 0.13g/8
Cs = 0.016 g
1 0.25Da
S gS
T T
1.23a DSS S g
0.20s
0.04s
0.492 18.45aS T
0.13 g
The University of the West Indies Seismic Research Centre email: [email protected]
48ETABS STRUCTURAL MODEL
The University of the West Indies Seismic Research Centre email: [email protected]
• Conclusions
- 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,
including TRINIDAD AND TOBAGO
- South West of Tobago, Toco and Chaguaramas have the
highest seismic hazard level in terms of Peak Ground
Acceleration (0.6 g for a RP=2475 years; 0.33 g for a
RP=475 years) for rock site conditions.
- For Port of Spain the expected peak ground acceleration
level is 0.58 g RP=2475 years; 0.33 g for RP=475 years;
for rock site conditions.
The University of the West Indies Seismic Research Centre email: [email protected]
50
Influence of seismogenic zones
Island of Trinidad
Cornell-McGuire approach
Hazard dominated by Zone 11
Port of Spain (Trinidad)
RP=2475 years
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
0.00 0.50 1.00 1.50 2.00 2.50 3.00
T(s)
SA
(g
)
SZ01
SZ02
SZ03
SZ04
SZ05
SZ06
SZ07
SZ08
SZ09
SZ10
SZ11
SZ12
SZ13
SZ14
SZ15
ALL
Transition zone
North of Paria P.
Trinidad Faults
The University of the West Indies Seismic Research Centre email: [email protected]
• What is the next job at UWI - SRC with
a possible collaboration of T&T
government ?
The University of the West Indies Seismic Research Centre email: [email protected]
52
Rodriguez (2003)
Site effect
The University of the West Indies Seismic Research Centre email: [email protected]
SITE EFFECTS EVALUATION
• Site effects: amplification of motion due to the presence of sedimentation (soil) - geotechnical hazard
We need a SEISMIC MICROZONATION:
A map of a small within a country, e.g. a City, that details the different levels of a specified
geotechnical hazard that may be triggered by an earthquake constitutes a Seismic Microzonation.
Collaboration project with Ministry of Planning
The University of the West Indies Seismic Research Centre email: [email protected]
Proposed single-mobile microtremors measurement sites (red points) at Port of Spain, Trinidad.
Applying the well-known H/V ratio technique proposed by Nakamura (1989) we can obtain the
fundamental period of the soil profile
at each measuring site.
The University of the West Indies Seismic Research Centre email: [email protected]
GEOPHON
E
LINE OF
GEOPHONES
12
3
4
5
6 7
SEISMIC REFRACTIONMICROTREMORS ARRAY
STRONG
MOTION
INSTRUMENTGPS
SCIENTIFIC EQUIPMENT
The University of the West Indies Seismic Research Centre email: [email protected]
THANK YOU
Questions ?