Active Faults In Peninsular Malaysia With Emphasis On Active Geomorphic Features Of Bukit Tinggi Region

Mustaffa Kamal Shuib, Mohammad Abdul Manap, Felix Tongkul, Ismail Bin Abd Rahim, Tajul Anuar Jamaludin, Noraini Surip5, Rabieahtul Abu Bakar, Mohd Rozaidi Che Abas, Roziah Che Musa, Zahid Ahmad 1Department Of Geology, University of Malaya, 50603 Kuala Lumpur.Minerals and Geoscience Department Malaysia, Headquarters Bangunan Tabung Haji, Jalan Tun Razak, 50658 Kuala Lumpur.3School of science and technology, Universiti Malaysia Sabah, 88999 Kota Kinabalu, Sabah.4School of Environmental and Natural Resource Sciences, UniversitiKebangsaan Malaysia, Bangi. Selangor.5Faculty of Engineering, Technology & Built Environment, UCSI University, 56000 Kuala Lumpur.6Malaysian remote Sensing Agency, JalanTun Ismail, 50480 Kuala Lumpur.7Malaysian Metereology Departmet. Jalan Sultan, 46667 Petaling Jaya, Selangor.

The evidences for active faulting, and the characteristics of these faults are discussed. Several fault segments within the Bukit Tinggi fault zone are deemed active. The Bukit Tingg fault zone is considered to be active and is a potential source of future earthquakes. The fault zone show the following active neotectonic geomorphic features: 1) displays geomorphic features indicative of recent fault activity; 2) show evidence for displacement in young (Late Quaternary) deposits or surfaces; and/or 3) is associated with a pattern of microearthquakes suggestive of an active faults.

Tectonic setting
Peninsualr Malaysia (Figure 1) is situated on SUNDALAND, the southern protrusion of the Eurasian Plate. Sundaland is a region that comprised of the Malay Peninsula and Maritime Southeast Asia islands of Sumatra, Java, Borneo and surrounding smaller islands. It is situated at the core of Sundaland that has been considered a tectonically stable region since the Cenozoic. Generally, it is considered as tectonically stable with low seismicity profile. It experienced dam induced seismicity of low magnitude (less than 4.5 on the Richter scale) at Kenyir Dam in 1985 Seimic hazard -Tremors from far-field earthquakes: The peninsula is bounded by two of the most seismically active plate boundaries. To the west the inter-plate boundary between the Indo-Australian and Eurasian Plates defined by the Sunda Subduction Trench and the inter-plate boundary between Eurasian and Philippine Plates to the east Phillipines Subduction Trench. It is situated close to the most seismically active plate boundaries between the Indian-Australian Plate and Eurasian Plate in the west and between Philippine Plate and Eurasian Plate in the east. It occassionally experienced tremors due to earthquakes from these far-field sources. -Tsunami: In also did not escape the 2004 megathrust tsumani. The tsunami raised the alarm that the penisula is not free from seismic hazard.

-Local earthquakes:
Since 2007 the peninsula is experincing ocassional earthquakes of local origin for example the 2007-09 Bukit Tinggi earthquakes. These events stirred awareness among the public and authorities on the potential seismic hazard and risk faced by the peninsula.
Thus, empirical evidence suggests that Malaysia is not totally free from seismic risks. Recent seismicity in Peninsular Malaysia has been confined to low levels with no clear association with existing mapped faults. The identification of active faults is the subject of this study.

Young active neotectonic defromation
The identification of neotectonic deformation and active faults in Peninsular Malaysia has been hampered by: 1) the comparative lack of fault studies; 2) extensive weathering of bedrock and extremely active erosion acting together to prevent the preservation of all but the most resistant geomorphic features; 3) large areas of thick forest vegetation, and 4) the probable low slip rates of the intraplate faults in Peninsular Malaysia.
These factors result in a lack of recognizable, long-lived surface faulting geomorphic features. Despite these shortcomings, Quaternary deformation investigations in Peninsular Malaysia have been successful and indicate that it is ongoing and that these activity may pose a seismic hazard (e.g., The fractures in the basalt are essentially vertical and are evident manifestations of reactivation of the older faults. In Southeast Johor at the edge of the Penyu basin, crustal uplift of 0.5 -0.8 m during the past 5000 years is suggested by an abrasion platform that is that much higher compared to the eustatic Holocene sea-level curve of the Peninsula which was established from almost a hundred radiometrically determined bioshoreline indicators. In the northwest on the shores of Langkawi, a 2500year old abrasion platform is cut by a long fault zone whose associated secondary structures suggest sinistral displacement. Active major faults Generally, major fault in the Malay Peninsula ( Figure 1) appeared to be inactive. However, a series of large earthquakes in recent years had changed the tectonic scenario in the Southeast Asian region, including the Peninsular Malaysia. In spite of its crustal stability, the 2004-Sumatera earthquake had caused horizontal shifts of GPS monuments in the Peninsula in the order of up to 7 mm. There are also indications of co-seismic uplifts. In Langkawi, stacked doublets of (recently live specimens) barnacle-oyster bands suggest uplift in the order of half a meter by the same event. The Malay Basin region offshore the Peninsula is on stable crust, and yet seismic shows major, deepreaching faults to approach the seabed to within 150 m, indicating activity on these structures to have persisted into the Pleistocene. The distribution of the epicentres within the viccinity of Bukit Tinng New Village on IFSAR is shown in Figure 5.The relationship the earthquake epicentres with the extracted lineaments is shown in Figure 6. Figure 7 shows the distance of epicenters from lineaments. The analysis noted that the earthquake epicenters are found diffuse in the vicinity along: a) the Bukit Tinggi fault Zone trend (NW) b) WNW trend along the Bukit Tinggi fault zone. c) E-W and d) NE trends, suggesting ongoing reacvtivation of these faults.This is consistent with the findings of JMG (2012) which suggest that the relationship of the recent earthquake epicentres with known faults as "established 2) Geomorphic features of active faulting To determine the active segments of the faults it is necessary to analyze the geomorphology of the area. In this study, we applied digital enhanced IFSAR images (figure 5) for data analysis. The digital enhanced IFSAR images study and interpretation is to assist in delineating small-scale neotectonic features and to define the orientation and direction of the investigated active fault segments. Practically, automatic and visual interpretation was used. This is regarded as the prime and most effective approach for identification of neotectonic or active fault geomorphic features. The following geomorphological features were picked up in the IFSAR analysis and verified in the field:

a) Primary neotectonic features/ landforms
Several morphotectonic pieces of evidence can be recognized from the IFSAR data. Among them, the most outstanding features are steep-sided basins, triangular facets and steep scarps.  These suggest that the alluvial basin is fault-controlled and have undergone internal displacements suggesting the basin infillings were subjected to internal deformation. Figure 11 shows a panoramic view of the alluvial plain bounded by steep scarps. Outcrops along the scarps reveal the presence of fine to coarse grain alluvial deposits (figure 12). These deposits contain large boulders at their base and exhibit warped bedding ( figure 12A). These implied that the alluvium have undergone neotectonic deformations.

b) Secondary neotectonic features
The drainage network derived from IFSAR DEM is shown in figure 13. It shows that the main drainage pattern is flowing from NW to SE. The distributaries flowed from N-S and from W to E. From the drainage pattern it is noted that there are several places where the streams form dog-leg pattern. From the pattern it was noted that the dog-legs are due to stream off-sets, beheadments and shifting streams ( figure 13 & 14).

a)
Stream off-sets ( figure 13 & 14).) can be located at several places along the river at several localities. At these localities the stream has been shifted for about 500m to form the dog-leg pattern. The offset line is generally extended on both sides along negative lineaments of about 5 km long bounded triangular facets with hour glass geometry typical of active faulting. One or two earthquake epicentres may aligned along the lineaments. These suggest young fault controlled on the stream offsets.

b)
Shifting streams ( figure 13& 14). At one locality the major stream form dog-legged pattern due to stream offsets of about 600m. Along the offset region a small quaternary basin developed bonded by steep scarps. In addition to that it was found several parallel curvilinear abandoned Remote-sensing information clearly indicates that the old faults are the most prominent fault traces, as observed from field, and satellite images. These faults trends in the NW-SE, NE-SW and N-S directions. The NW-SE Bukit Tinggi Fault and the N-S Benus and Karak Faults mostly follows the predated regional geological structures which developed prior to the Cenozoic times. Others interesting lineament features, which are regarded as old faults, are also observed in the east-west and northeast-southwest directions.
Within the Bukit Tinggi fault zone, IFSAR revealed the presence of Quaternary basins, and young geomorphic or active tectonic landforms such as stream offsets, beheaded streams, steep scarps and faceted spurs. They formed short lineaments that coincided with earrthquake epicentres. The are believed to be the surface menisfestation of active faults that occurred as short segments within the Bukit Tinggi fault zone. Most of these active fault segments trend NW_SE parallel to the main fault zone. Others trend WNW-ESE,and NNE-SSW. From the sense of offsets they exhibit both dip -slip and strike-slip movements with sinistral motions likely due to the secondary effect of the active movements along the Bukit Tinggi fault zone.
At Bentong and Karak area, the Benus and Karak faults also shows evidences of active faulting in the form of stream offsets. It is of particular interest that these recently reactivated faults produced active geomorphic features which were likely related to paleoearthquakes suggesteing that they are active faults. Based on the presence of active geomorphic features, the magnitude of the paleoearhquake that occurred must be not less than 6 on tghe Richter Scale.
Further study is in progress to determine the ages of these paleoearthquake occurence to determine their magnitude, slip rates and reccurrence intervals for seismic hazard and risk analysis.

CONCLUSIONS
In this research, It is concluded that there are several likely active faults in Peninsular Malaysia based on earthquake epicentres distribution. Present geomorphic study from satellite images and earthquake evidences clearly depicts that within the NW trending Bukit Tinggi fault zone, there are severa strands of both oblique and parallel active fault segments suggesting that the main Bukit Tinggi fault is an active fault. Offsets streams also suggest active faulting along the Benus and Karak faults.
They were ancient faults that were reactivated in the Quaternary period and continued into the present. The magnitude of paleoearthquake estimated from the activity and stream offsets suggest a minimum of 6 magnitude on the Richter scale have affected the region due to movements along these faults. Over the past decades, Peninsular Malaysia has experienced mild earthquakes. Virtually all earthquakes recorded in Peninsular Malaysia are under magnitude 5.0. However, the regognition of active faults exhibiting active tectonic landforms suggestes that these faults have produced damaging earthquakes before and have potential to trigger similar tremors in the future.