seismicity and seismic hazard assessment in...
TRANSCRIPT
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Seismicity and Seismic Hazard Assessment in Bangladesh:
Reference to Code Provisions
Dr. Tahmeed Malik Al-Hussaini
Associate Professor Department of Civil Engineering
Bangladesh University of Engineering & Technology
Meeting on Seismic Hazard in Asia
ICTP, Trieste, Dec.4-8, 2006
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CONTENTS:
� Earthquake Occurrence in and around Bangladesh
� Seismic Hazard Assessment
� Earthquake Vulnerability of Urban Areas
� Local Soil Effects
� Seismic Instrumentation
� Remarks on Research Activity
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BangladeshLandform:- Area: 147,570 sq.km- Population 150 million- 230 Rivers 2,140 km- Deltaic plain of Ganges, Brahmaputra & Meghna- Flat and low topography- Hills in SE and NE- 700 km long coastline
Dhaka
Chittagong
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EarthquakeEurasian
Plate
Indian Plate
� Bangladesh is located in a tectonically active region close to the plate boundaries of the north moving Indian plate and the Eurasian plate to its north and east.
� Lack of earthquake awareness and preparedness may lead to massive disaster if major earthquake strikes.
� Recent tremors have frequently shaken the south-eastern region (Chittagong), some have caused damages.
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SEISMICITY IN AND AROUND BANGLADESH
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Strong Earthquakes affecting Bangladesh
2507.1Dhubri Earthquake3 July, 1930
1507.6SrimongalEarthquake
8 July, 1918
2308.7Great Indian Earthquake
12 June, 1897
1707.0Bengal Earthquake14 July, 1885
2507.5Cachar Earthquake10 Jan, 1869
Distance (km) from Dhaka
MagnitudeEarthquakeDate
Five earthquakes (M≥≥≥≥7) during 1869-1930 (61 years)
No large earthquake in last 50+ years!
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1897 Great Indian Earthquake (M=8.7)
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1930 Dhubri Earthquake (M=7.1)
1918 SrimangalEarthquake (M=7.6)
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Moderate Damaging Earthquakes in Bangladesh:Last 10 Years
� May 1997 earthquake in Sylhet (M=5.6): Wall Cracks.
� Nov. 1997 earthquake at Myanmar Border (M=6.0): Collapse of a building in Chittagong city (18 deaths).
� July 1999 earthquake in Moheshkhali Island (M=5.1): Serious damage and collapse of mud-walled houses, Serious damage to a cyclone shelter column
� Dec 2001 earthquake near Dhaka city (M=4.2-4.8): Panic & Injuries
� July 2003 earthquake in Rangamati (M=5.6): Serious damage to brick masonry buildings and mud-walled houses. Major cracks in a building in Chittagong.
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Concrete Frame Building is common in urban areas.
1997 collapse of this reinforced concrete frame building in Chittagong city was trigerred by M=6.0 earthquake more than 100 km away.
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Cyclone Shelter
Column damage during 1999 Moheshkhali earthquake (M=5.1)
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Mud-walled house in rural areas (damaged/collapsed during recent earthquakes)
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Unreinforced brick masonry buildings with concrete roof common in rural and urban areas
Damaged in an M=5.6 earthquake
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Long soil crack along the river
Slumping of soil at river bank
2003 M=5.6 Rangamati Earthquake
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SEISMIC HAZARD ASSESSMENT FOR
BANGLADESH:
REFERENCE TO 1993 BUILDING CODE
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Z=0.25
Z=0.15
Z=0.075
Dhaka
INDIA
INDIA
INDIA
Bay of Bengal
Chittagong
Seismic Zoning Map of India (IS 1893, 2002)
1993 Building Code
Seismic Zoning Map of Bangladesh
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Earthquake Catalogue
1845-2005
M≥≥≥≥3.5 Earthquakes
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Checking Completeness of
Earthquake Catalogue
M=5
0
200
400
600
800
1000
1200
1400
1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
Cu
mu
lati
ve N
o.
of
EQ
M=6
0
20
40
60
80
100
120
140
160
180
1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
Cu
mu
lati
ve N
o.
of
EQ
M = 5
M = 6
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Magnitude-Frequency relationship for Entire Region
a = 5.21b = 0.81
Entire Region
0.001
0.010
0.100
1.000
10.000
100.000
1000.000
3 4 5 6 7 8 9 10
Magnitude(M)
Cu
mu
lativ
e A
nn
ual
Fre
qu
ency
( νν νν)
Log(ν) = 5.214 - 0.809*M
No. of Earthquakes = 2122
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Five Seismic Source Zones
15
17
19
21
23
25
27
29
31
82 84 86 88 90 92 94 96 98Longitude
Lat
itud
e
M>8.0
8.0>M>7.0
7.0>M>6.0
6.0>M>5.0
1845-2005
Table 2: Computed a, b values for five seismic source zones
Zone Location Number of earthquakes
Mmax a b
1 Assam fault zone 685 8.7 4.449 0.764 2 Tripura fault zone 1330 7.7 5.396 0.9 3 Sub-Dauki fault zone 59 7.6 2.598 0.621 4 Bogra fault zone 9 7.0 3 0.809 5 Coastal source zone 39 5.7 3.389 0.793
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Magnitude-Frequency relationship
Tripura Fault ZoneAssam Fault Zone
Assam fault zone
0.001
0.010
0.100
1.000
10.000
100.000
3 4 5 6 7 8 9 10
Magnitude(M)
Cu
mu
lativ
e A
nn
ual
Fre
qu
ency
( νν νν)
Log(ν) = 4.449 - 0.764*M
No. of Earthquakes = 685
Tripura fault zone
0.0010
0.0100
0.1000
1.0000
10.0000
100.0000
3 4 5 6 7 8 9 10
Magnitude(M)C
um
ula
tive
An
nu
al F
req
uen
cy( νν νν
)
Log(ν) = 5.397 - 0.9*M
No. of Earthquakes = 1330
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Eight Seismic Source Zones
15
17
19
21
23
25
27
29
31
82 84 86 88 90 92 94 96 98Longitude
Lat
itud
e
M>8.08.0>M>7.07.0>M>6.06.0>M>5.0Bangladesh
1845-2005
Table 3: Computed a, b values for eight seismic source zones
Zone Location Number of earthquakes
Mmax a b
1 Nepal, Darjeeling 315 8.3 4.872 0.929 2 Meghalaya, Assam, Bhutan 270 8.7 3.789 0.705 3 NE Assam, Arunachal 86 8.6 2.616 0.571
4 Rangpur, Bogra, Dinajpur,
Mymensingh, Dhaka, Sylhet 47 7.6 2.556 0.592
5 West Sylhet, Tripura 38 6.5 3.116 0.73 6 Southwestern Coastal Region 8 5.7 2.9 0.809 7 Chittagong 41 6.5 3.59 0.828 8 Mizoram, Manipur, NW Myanmar 1092 7.6 5.467 0.933
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Magnitude-Frequency relationship
Zone 2
0.0010
0.0100
0.1000
1.0000
10.0000
100.0000
3 4 5 6 7 8 9 10
Magnitude(M)
Cu
mu
lativ
e A
nn
ual
Fre
qu
ency
( νν νν)
Log(ν) = 3.789 - 0.705*M
No. of Earthquakes = 270
Zone 7 (Chittagong)Zone 2 (Assam)
0.0001
0.0010
0.0100
0.1000
1.0000
10.0000
3 4 5 6 7 8
Magnitude(M)
Cu
mu
lativ
e A
nn
ual
Fre
qu
ency
( νν νν)
Log(ν) = 3.59 - 0.828*M
Zone 7
No. of Earthquakes = 41
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This is not the final hazard map!
Estimation of Probabilistic seismic hazard (PGA in cm/sec2) for Bangladesh
(8 seismic source zones, return period 500 years)
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Peak Ground Acceleration (PGA) in g
Large Earthquakes greater than 7.4 have not been considered here, which will be considered later.
BUET-ICTP Research Collaboration
May-June 2006
DETERMINISTIC SEISMIC HAZARD ASSESSMENT FOR
BANGLADESH
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EARTHQUAKE VULNERABILITY OF
URBAN AREAS
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DHAKA CITY
0
2
4
6
8
10
12
1600 1700 1800 1900 2000
Year
Po
pu
lati
on
(m
illio
n)
A congested city Population growth
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Old Brick Buildings and Roof framing
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Risky Electrical Wiring
Narrow Lane
Gas Oven
INDUCED
FIRE RISK
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Narrow RoadwaysHigh-Rise Building
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Residential Area
Built in 1990s
Built in 1960s
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Irregular Building
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Open Ground Story (Car parking)
6-Storied Apartment Building
Possibility of pounding
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Predicted Damage due to Intensity VIII earthquake in selected parts of Dhaka city
Thana Sutrapur Lalbagh WestDhanmondi
URM:RCF buildings 65 : 35 49 : 51 32 : 68
Complete/PartialCollapse of URM/RCFbuildings
5.8 % 5.5 % 5.3 %
Number of people athigh risk of death andserious injury
18,600 27,300 18,800
Serious damage ofbuildings
16.7 % 13.5 % 10.1 %
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LOCAL SOIL EFFECTSIN DHAKA CITY
(MODERATE SEISMIC RISK):
REFERENCE TO 1993 BUILDING CODE
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Bangladesh National Building Code (1993)
� Soils classified as S1, S2, S3, S4� Three methods for seismic analysis
(a) Equivalent Static Force …….Soil factor S=1, 1.2, 1.5, 2.0
(b) Response Spectrum……Response Spectrum Curves for S1, S2, S3
(c) Time History Analysis
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0
0.05
0.1
0.15
0.2
0 2 4 6 8 10
No. of Stories
Bas
e S
hea
r C
o-e
ffic
ien
t
IBC (2000)
BNBC (1993)
BNBC (1993)
vs.
IBC (2000)
Taller buildings (6 stories or more) are subjected to larger base shear than what BNBC suggests
Soil type: S3
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Soil type from Satellite Images
(Kamal, 2004)
Soil type based on boring data
DHAKA CITY
Soil classification in Dhaka city using borehole data (predominantly S2 and S3)
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Response Spectrum (wave propagation analysis) obtained for Various S2 Sites in Dhaka City
0
2
4
0 1 2 3
Period (Sec)
Spec
tral
Acc
eler
atio
n/g
zAshkona
Basabo
Lalbagh
Badda
Nikunja
Tikatuli
Soil S2, BNBC
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Response Spectrum (wave propagation analysis) obtained for Various S3 Sites in Dhaka City
0
2
4
6
8
0 1 2 3
Period (Sec)
Spec
tral
Acc
eler
atio
n/g
ZBHSGoranKeller MorhRampura(Banasree)SabujbaghUttaraWest RampuraBasundharaNiketonEskatonSoil S3, BNBC
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Remarks on Local Soil Effects:
� Equivalent static load method:
BNBC appears to be unsafe for buildings 6 stories and
taller when compared with recent IBC code.
� Response spectrum method:
BNBC design response spectra appear to
underestimate peak spectral acceleration as shown by
wave propagation analysis results.
� Geotechnical earthquake design provisions in BNBC
needs major revision.
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DIGITAL SEISMIC INSTRUMENTATION
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� 7 Accelerometer (JMBA-BUET) since 2003
� 4 Broad Band Seismometer + Accelerometer (BMD) to be installed shortly
� 6 Short Period Seismometer (BMD) planned for other locations.
Digital Seismic Stations
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Jamuna Bridge Seismic Instrumentation Project� 4.8 km long base-isolated bridge designed for M=7.0 magnitude
earthquake in Bogra fault zone at a distance of 25 to 50 km � Seismic Instrumentation (accelerometers) installed in 2003 on bridge
and free-field stations� Rare recordings of events
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Numerical Study: Isolated vs. Non-isolated Bridge(Ahmad, Al-Hussaini, Choudhury, 1999)
Numerical Model of Bridge Module
Isolator Force-Displacement loop
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Seismic Data (recorded July 16, 2004)
Free Field (West End) Bridge: Pile Cap
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Final Comments on Research Activity
Ongoing Research:� Probabilistic Seismic Hazard Assessment� Analysis of Free-Field Record / Bridge Response� Vulnerability Assessment of Structures� Local Soil Effect� Deterministic Seismic Hazard Assessment (in collaboration with
ICTP)
Proposed Activity in Collaboration with ICTP & Network Partners:� Formation of Suitable Earthquake Catalogue� Deterministic Seismic Hazard Assessment� Seismic Source / Geologic Structure Modelling� Local Site Effect
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Thank you !