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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