Download 1. Geological assesment of the earthquake sources and hazard in

SEMINAR TEKNIKAL GEMPABUMI
JMM, 20 December 2011
GEOLOGICAL ASSESSMENT OF
THE EARTHQUAKE SOURCES
AND HAZARD IN MALAYSIA
By
Alexander Yan Sze Wah
JMG Sabah
TOPICS
1.  Introduction
2.  Tectonic Setting and Seismicity of
Malaysia
3.  Geological assessment of the
earthquake sources and hazard in
a) 
b) 
c) 
Peninsular Malaysia
Sarawak
Sabah
4.  Concluding remarks
INTRODUCTION
Seismic activities from 2007-2011:
•  More than 45 strong earthquakes (>6 Mb)
occurred in Sumatra. Many were felt in
Peninsular Malaysia, with intensity up to V in
the MMI scale.
•  Local tremors ( 1.7 – 3.5Mb) at Bukit Tinggi,
Jeruntut, Manjung & Kuala Pilah
•  24 minor earthquakes, 2.6 – 5.2 Mb recorded
in Sabah
•  Several strong earthquakes from Celebes
sea, Sulawasi and Mindanao felt in Tawau &
east coast of Sabah
INTRODUCTION
Location of strong Sumatran earthquakes (>6 Mb) from 2007 -2011.
Many were felt in Peninsular Malaysia with intensity up to V (MMI scale)
Source: USGS
INTRODUCTION
Local earthquake occurrences from 2007 - 2011
•  Peninsular Malaysia –
  24 in Bukit Tinggi area ( 1-7 to 3.5 Mb)
  1 in Jeruntut ( 3.2 Mb)
  1 in Manjung ( 2.8 Mb)
  4 in Kuala Pilah ( 2.6 to 3.2 Mb)
  1 in Kenyir Dam ( 2.6 Mb)
•  Sabah – 24 (magnitude : 2.6 to 5.2 Mb)
•  Sarawak – 1 (magnitude: 3.5 Mb)
TECTONIC SETTING OF MALAYSIA
Malaysia – divided into 2 major tectonic units;
1.  Western relatively stable Sundaland.
2.  An eastern mobile unit of Sabah and part of Sarawak.
Source:
Tjia, 2006
TECTONIC FRAMEWORK
•  Bordered to the west and to the south
by the seismically active Sunda-Banda
Volcanic Arc; subduction of the IndianAustralian plate at 6-8 cm/yr
•  To the east by the Philippines-Pacific
Plate which moves at 10 cm/yr
INTERACTION BETWEEN THREE MAJOR
TECTONIC PLATES
5 cm/yr
Eurasian –
Sunda Plate
10 cm/yr
Phillipines-Pacific
Plate
7 cm/yr
Indian-Australian 5-6 cm/yr
Plate
Source: USGS
SEISMICITY OF MALAYSIA
•  Malaysia , situated in the stable Sundaland,
is considered a low seismic country
•  Earthquake sources in Malaysia
–  Peninsular Malaysia- distant source, from
Sumatra, local re-activated faults.
–  Sarawak – local source; active faults
–  Sabah – local source ( many active faults)
and offshore- the Sulu & Celebes Seas
Seismic Zones of Southeast Asia
Bur
ma
North
Indochina
Stable
Sunda
Borneo
Java Back Arc
Java
Distant earthquake source
Distant earthquakes that influenced
Peninsular Malaysia, particularly the West
Coast are originated from two earthquake
faults:
•  The Sumatran subduction zone and
•  The Sumatran strike slip fault
Strong & Major Sumatran Earthquakes
(2007-2011)
Raub-Bentong
Suture
Deadly Earthquakes in Sumatra
DATE
2004 Dec 26
2005 Feb 28
2007 Mar 6
2007 Sep 12
2008 Feb 20
2009 Sep 30
2010 Oct 25
2011 Sep 5
MAG DEP LOC
FATALITIES
9.1 30km
Aceh
227,898
8.6
30 km Nias
1,313
6.4
19 km Bt Tinggi
67
8.5
34 km Bengkulu
25
7.4
26 km Simeulue
3
7.6
81 km Padang
1,117
7.8
20 km P.Mentawai
445
6.7
91 km N. Sumatra
10
Earthquake sources around Sumatra
1.  thrust earthquakes on the Sumatran
subduction fault,
2.  strike-slip earthquakes on the Sumatran
fault,
3.  deeper earthquakes within the subducting
lithosphere, and
4.  volcanic earthquakes
Earthquake sources around Sumatra
Lock
ed
Fault
Zone
After McCaffrey, 2009
The “subducting” oceanic plates drop deeper into the earth to
about 30 km beneath Sumatra, the megathrust resists slippage.
Edges of the plates become coupled, or locked together.
Tremendous strain builds up, over many decades or even longer
than a century, until a section of the megathrust gives way.
Mechanic of Oblique Subduction
The direction of convergence of
the India Plate relative to the
Sunda plate (thick arrows ) is
oriented oblique to the
orientation of the interplate
thrust (i.e., trench axis).
The Sumatra subduction zone is
characterized by decoupled faulting. In
this case, nearly pure thrust faulting
occurs along the interplate thrust and
strike-slip faulting occurs in the
overriding plate, most notably along the
Great Sumatran Fault.
The plate kinematics for oblique subduction in the Sumatra region is much more
complex. Process now known as slip partitioning , where the two plates do not converge
at a right angle to the strike of the trench, it requires smaller overall shear force to share
the shearing (trench-parallel) component of the relative motion between two separate
faults instead of on one fault.
Deformation of the
overriding plate
leads to larger
complexities in plate
motions.
after McCaffrey,
2009
P-wave
tomography
model by
Pesicek et al,
2008.
Complex slab
subduction
beneath
northern
Sumatra,
folded at
depth
Complex folded subducted slab beneath northern Sumatra and
Malay Peninsula
The fold in the slab
below northern
Sumatra, at 190 to
530 km, is a result of
deformation of the
Indo-Australian
Plate and act as a
barrier to rupture
along the megathrust.
Study the cause and
timing of folding, and
the details of its
potential influence on
stress accumulation
and rupture initiation
and propagation.
Aceh (2004) and Nias (2005)
Cross section across the Sumatra Forearc at Nias
Bt Tinggi
Date: 2007 Mar 6
Mag: 6.4 Mb
Depth :19 km
Fatalities: 67
Occurred on the
strike-slip
Sumatran fault.
Bengkulu
Date: 2007 Sep 12
Mag: 8.5 Mb
Depth : 34 km
Fatalities: 25
Sumatran subduction
megathrust fault
Padang
Date: 2009 Sep 30
Mag: 7.6 Mb
Depth : 81 km
Fatalities: 1,117
The Padang Earthquake
Oblique-thrust faulting near the subduction interface plate boundary
between the Australian plate, which moves north-northeast and the
Sunda plate at a velocity of approximately 60 mm/yr. The Padang
Earthquake occurred due to underthrusting within the subducting
Australian Plate rather than on the plate interface itself.
Rupture zones of the Sumatran megathrust fault, offshore
Sumatra in 1797, 1833, 2000- 2008
Future megathrust
2004
2005
8.5
1797
Future
megathrust 2007
2000
GLOBAL SEISMIC HAZARD ASSESSMENT
PROGRAMME (GSHAP) SEISMIC HAZARD MAP OF
SOUTH EAST ASIA (1999)
USGS (2008)
Seismic
Hazard Map
Of Western
Indonesia.
PGA with 10%
probability of
exceedance in
50-yr hazard
for Peninsular
Malaysia
ranged from
0.02 -0.08 g
0.1 g
0.05 g
< 0.05 g
Revised Seismic Hazard
Map of Indonesia by
Tim Revisi Peta
Gempabumi Indonesia
headed by Masyhur
Irsyam et. al. 2010
Maximum Observed
Intensity map of
Peninsula Malaysia
(1805-2007)
II
III
V IV (PGA:
(PGA:
0.03-0.04 g)
0.015-0.02 g)
(Source: Leyu, 2008)
SEISMOTECTONIC MAP OF
PENINSULAR MALAYSIA
MALAY BASIN
Impounding of Kenyir
Dam, Induced earthquake,
4.1 Mb in 1985
IR
LEB
G
TON
LT
FAU
BEN
URE
SUT
KL FAULT
PENYU BASIN
WEST
NATUNA
BASIN
EARTHQUAKE OCCURRENCES
IN PENINSULAR MALAYSIA
2007 -2010
  24 in Bukit Tinggi area
(1.7 to 3.5 Mb) - 2007 to 2009
  1 in Jeruntut ( 3.2 Mb) - 2009
  1 in Manjung ( 2.8 Mb) - 2009
  4 in Kuala Pilah ( 2.6 to 3.2 Mb)
-2009
  1 in Kenyir Dam ( 2.6 Mb)- 2010
BUKIT TINGGI EARTHQUAKES
•  Series of weak earthquakes, magnitude
from 1.7 to 3.5 Mb in 2007 to 2009 at the
Bukit Tinggi area are at depth of 2.3 to
6.7 km.
•  Slight damage to SMK Bt Tinggi and
the Police Station.
•  First wave motion recorded at several
seismic stations indicate faulting.
•  Suspected re-activation of the Bukit
Tinggi Fault. Strike-slip movement
BUKIT TINGGI FAULT
FOCAL MECHANISM SOLUTION USING PWAVE MOTIION FOR THE BUKIT TINGGI
EARTHQUAKE
FMS using the Pwave first motion
recorded at 6 seismic
stations
STRIKE-SLIP
FAULTING
FAULT PLANE
TRENDING 318O
DIPPING 80O NE
SINKHOLES - INDUCED FROM 2004 SUMATRAN
EARTHQUAKES
SINKHOLES - INDUCED FROM 2005
SUMATRAN EARTHQUAKES
SINKHOLES - INDUCED FROM 2007 SUMATRAN
EARTHQUAKES
SEISMICITY OF SARAWAK
•  Since 1874 – 21 earthquakes,
magnitude from 3.5 – 5.3 Mb
•  Jan 2010 - an earthquake of 3.5 Mb near
Niah
•  Major active faults
–  Tubau Fault – 100 km long, N-S trending,
left-lateral strike-slip fault
–  Bukit Mersing Fault
–  Kelawit Fault
–  Tinjar Fault
–  West Baram Fault
MAJOR FAULTS IN SARAWAK
EARTHQUAKE- GENERATING FAULTS IN
SARAWAK
TUBAU FAULT
1 May 2004
5.2 Mw,
Depth: 12 km
BUKIT MERSING FAULT
12 Feb 1994
5.2 Mb
Depth: 28km
25 Jan 2010
3.5 Mb
BAKUN
DAM
Maximum Observed Intensity map of
Sabah and Sarawak (1875-2007)
(PGA:
0.1-0.15 g)
VII
(PGA:
0.03-0.04 g)
VII
V
VI
VI
VI
V
(PGA:
0.06-0.07 g)
VIII
(PGA:
0.25-0.3 g)
IV
(Source:
Leyu, 2008)
SEISMICITY OF SABAH
•  Sabah has the most earthquakes
–  94, from 1897-2011
–  Two destructive earthquakes – in 1966 and
1991, caused substantial damage
•  North-West Sabah - influenced by the
spreading and opening of the South China
Sea Basin, that ceased 17 Ma ago.
•  Eastern Sabah – influenced by the Cagayan
Ridge Volcanic Arc in te NE, the Sulu Trench
and the Sulu Sea Volcanic Arc.
SEISMIC ZONES OF SABAH
•  Earthquakes occurred in Sabah over a wide
area.
•  24 earthquakes from 2007 to 2011 of
magnitude 2.6 to 5.2 Mb.
•  5 earthquakes ( 2.9 to 4 Mb) in 2011
•  Three main seismic zones which have a high
concentration of earthquake, namely:
–  the Central-North (Ranau) Zone,
–  the Labuk Bay - Sandakan Basin Zone, and
–  the Dent - Semporna Peninsula Zone
EARTHQUAKE OCCURRENCES 2007-2011
SEISMIC ZONES OF SABAH
CENTRALNORTH
ZONE
LABUK BAYSANDAKAN
BASIN ZONE
DENTSEMPORNA
PENINSULA
ZONE
CENTRAL-NORTH SEISMIC ZONE
•  Lies within a box-like overthrust sheet, 700 x
300 km known as the Northwest Sabah
Overthrust Sheet (Tjia, 2006)
•  Many major Quaternary faults, trending NESW, E-W and NW-SE,
•  Mainly, normal and strike-slip faults
•  Many are active and potentially active and
are likely source of earthquakes
•  Earthquakes magnitude from 2.6 to 5.3 Mb
and felt intensity from V to VII (MMI scale)
CENTRAL-NORTH SEISMIC ZONE
The 1966 & 1991 Earthquakes in Ranau
1966. 5.3 Mb,
depth 52 km
Landslide
Massive structure
damage to the
rubbish chute wall of
the teacher's quarter,
SM Mat Salleh, Ranau,
Sabah by the
earthquake on
26/5/91 .
1991, 5.1Mb,
depth 18 km
ACTIVE FAULTS
•  Earthquake-generating faults
–  Parancangan Fault (27 April 2010, 2.9 Mb &
23 Jun 2011, 3.2 Mb )
–  Mensaban Fault, normal-oblique, striking
WNW-ESE ( 23 July 2009, 3.4 Mb)
–  Mamut Fault ( 29 Sept 2011, 2.9 Mb)
–  Kadamaian Fault (4 Oct 2011, 2.9 Mb)
•  Potential earthquake-generating faults
–  Lobou-Lobou Fault (left-lateral strike-slip,
trending N20oE )
EARTHQUAKE-GENERATING FAULTS
IN THE RANAU-KUNDASANG AREA
29 Sept 2011
4 Oct 2011
23 July 2009
27 Apr 2010
18 May 1966
5.3 Mb
Depth: 52 km
26 May 1991
5.1 Mb,
Depth: 18 Km
23 Jun 2011
KEDAMAIAN FAULT
MENSABAN FAULT ZONE
GEOLOGY MAP OF THE RANAU AREA
DAMAGES CAUSE BY THE MENSABAN FAULT
40 cm
21 cm
A Pre-school building at
Kg. Kauluan, severely
damaged. Located near
the 23 July 2009
earthquake epicentre of
magnitude 3.4 Mb
Vulnerable areas in Ranau that are
exposed to seismic induced hazards
•  Areas of steep terrains underlain by highly
fractured and weathered, argillite, that is
metamorphosed to phyllite, of the Trusmadi
Formation is susceptible to slope failure
from ground shaking triggered by
earthquake.
•  Pinosuk Gravel
Pinosuk Gravel
DENT-SEMPORNA PENINSULA ZONE
•  Has the most and frequent earthquake
occurrences in Sabah with felt intensity up to
VIII (MMI scale)
•  Related to the southwesthern part of the Sulu
Volcanic Arc – subduction of the Sulu trench
towards SE.
•  Major NE and ENE trending normal and
thrust faults
•  Subject to NW-SE and E-W compressions
•  Vulnerable areas- coastal alluvial and the
Ayer Formation (melange and broken
formation)
DENT-SEMPORNA PENINSULA ZONE
Earthquake-generating Faults in
Dent- Darvel Bay Area
•  Darvel Bay- Lahad Datu area
–  1976 earthquake caused by Lahad Datu
Fault, ENE-trending normal fault
–  Magnitude 5.8 Mb, depth 33 km, caused
damages to several buildings
•  Dent Peninsula
–  earthquake caused by the active Tabin
Thrust Fault,
–  FMS of the 1994 earthquake, located on
the Tabin Fault of magnitude 5.7Mw, depth
34 km
EARTHQUAKE OCCURRENCES (2007 tO 2011, in
green) IN THE LAHAD DATU- DARVEL BAY AREA
SEGAMA VALLEY AREA
•  Two earthquake-generating faults, not
recognized earlier as active fault
•  Danum Fault, has produced an
earthquake of 3.3 Mb on 19 Nov 2008
•  Binuang Fault – generated earthquake of
4.3 Mb on 18 May 2008
•  Two earthquakes, 3.5 Mb & 4 Mb on 14
Oct 2010 & 14 Jun 2011 respectively at
the same location, in the Bangan Basin
SEGAMA VALLEY AREA
3.5 Mb,14 Oct 2010
4 Mb,14 Jun 2011
Bangan
Basin
3.3 Mb,19 Nov 2008
4.3 Mb,18 May 2008
5 0 0 km
6 0 0 km
6.6 Mb
04/10/09
6.6 -7.6 Mb
23-29/07/10
Depth >500 km
6.5 Mb
10/02/11
Gorontalo-Minhasa Trench
7.4 Mb
16/11/08
5.5 Mb
6.1 Mb
2/12/11
13/12/11
Depth: 30-160 km
5.5 Mb
06/10/10
Philippine Trench
7 0 0 km
Recent strong earthquakes from the
Gorontalo-Minahasa and Cotabato trenches
CONCLUDING REMARKS
•  Need constant monitoring of the Sumatra
subduction zone and Sumatran strike –slip fault
which are the sources of earthquake hazard for
Peninsular Malaysia .
•  Significant increase in seismic activity in Sabah
in the past 5 years. Frequency of earthquakes
has increased from 1-2 /yr to 5/ yr since 2007
•  Need to produced Earthquake Hazard Prone
Map for Sabah to be based on geology
(lithology, morphology and geological structure),
intensity scale, seismicity and PGA.
THANK YOU