Understanding the recent Sabah earthquake

and other seismogenic sources in North West Borneo

by Dr. Afroz Ahmad Shah

Sabah is on the Sunda Plate, and it is located in a tectonically dynamic margin of Borneo where it is surrounded by active plates of the Sunda, Indo-Australian, and Philippines Sea plates [1]. Thus, the regional seismological map in Fig. 1a shows a highly concentrated distribution of earthquakes around this region. However, earthquake distribution within NW Borneo is very scarce and based on this data the earthquake hazard is generally assumed to be negligible. This interpretation, however, seems challengeable because a number of small to medium magnitude earthquakes have occurred in this region. A thorough investigation is therefore warranted, so that all seismogenic sources can be mapped. There are two major reasons: Firstly, earthquake affects life directly. For example, the recent (June 2015) Moment Magnitude-6 earthquake that occurred 19 km north of Ranau, has caused unfortunate loss of 18 lives and significant damage to properties [2]. It could have been avoided if earthquake hazard information was provided. Secondly, the mapping of active and inactive geological structures is required to gain a better understanding of the scale of tectonic-complexity in the region.

Figure 1A. Regional tectonic setting of NW Borneo. The seismological data from Incorporated Research Institutions for Seismology (IRIS) shows highly concentrated distribution of earthquakes around the region. However, within NW Borneo earthquake distribution is very scarce, and based on this data the earthquake hazard is generally assumed to be negligible, which is questionable.
Figure 1A. Regional tectonic setting of NW Borneo. The seismological data from Incorporated Research Institutions for Seismology (IRIS) shows highly concentrated distribution of earthquakes around the region. However, within NW Borneo earthquake distribution is very scarce, and based on this data the earthquake hazard is generally assumed to be negligible, which is questionable.

The fault plane solution of the available seismological data in Fig. 1b shows a few medium sized earthquakes in Borneo, and these are mainly related to normal faulting. These indicate a northeast-southwest fault plane with a northwest or southeast dipping plane. The recent earthquake was hosted on a similar fault, which must be located close to the Sabah region. The topographic expression of such a fault is visible on the freely available Google satellite images. Some portions of this fault zone had been previously mapped [3]. However, a detailed investigation is required to map the entire fault zone, and work on ground is essential to better understand, and quantify the past, and the latest slip on the fault.

Figure 1B. The recent seismological data is superimposed onto the topographic image, which shows a large number of earthquakes on the west of study area, these are related to the subduction process. A significant number of earthquakes are clustered in and around Sabah, and these are mostly shallow focus and are a combination of normal, strike-slip and thrust fault related (shown as beach balls). This suggests active nature of faulting and thus topographic and geomorphic signatures are required to be mapped in detail.
Figure 1B. The recent seismological data is superimposed onto the topographic image, which shows a large number of earthquakes on the west of study area, these are related to the subduction process. A significant number of earthquakes are clustered in and around Sabah, and these are mostly shallow focus and are a combination of normal, strike-slip and thrust fault related (shown as beach balls). This suggests active nature of faulting and thus topographic and geomorphic signatures are required to be mapped in detail.

The cause of earthquakes in Borneo is yet to be determined, primarily because all the seismogenic faults have not been mapped. Nevertheless, the mapped fault traces, crossing Sabah, mainly show normal slip with both northwest and southeast dipping fault plane, possibly a horst-graben (these structure form during normal faulting where faults dip in opposite direction) regional structure. This clearly indicates northwest-southeast extension in Fig. 2, which is complimented by the recent GPS data in a fixed NW Borneo reference frame where some stations show northwest-southeast regional extension motion. The relatively well-studied northwest-southeast trending fold and thrust belt to the west of Sabah [3-9] indicates NW-SE compression, which is attributed to large crustal-scale gravity-driven mechanism, the orogenic collapse of the NW Borneo since 1.9 Myr [3].

Thus, the current understanding of active tectonics of NW Borneo is at a very fundamental stage, and science is slowly accumulating to get a better picture of the geological and tectonic architecture of the region. However, extensive work is required to grasp the tectonic versus gravity driven deformation nitty-gritty in the area.

Living with earthquakes

The earthquake science has greatly progressed over time, and with new insights coupled with modern technologies, a comprehensive model can be developed. This may help us in developing and implementing new strategies reduce any earthquake threats in the near future. Prediction of earthquake events however has not been achieved, and it has failed because the science of earthquake is complicated, and needs to be developed before earthquake prediction may finally become a possibility [10; 11]. For example, the recent knowledge of major earthquake in the Himalayas suggests that the earthquake generally did not follow a pattern but occurred randomly. This means that the concept of a rather regular return time between catastrophic earthquake is probably not relevant for the Himalayas [12]. Nonetheless, much progress has been made in understanding of the cause of earthquakes, and one must learn how to live with earthquakes without a successful prediction in sight. This could be achieved if one would strictly abide by the strict construction standards, careful geological evaluation of building sites, and public education.

Such practices are followed in many developed nations; for example, Japan has achieved a major milestone in building earthquake resistant structures and a scientifically aware society. Unfortunately, a large number of people live in the developing world, where these techniques remain sadly out of reach [13] because of the various limitations to information, poverty, corruption, illiteracy and poor administration [14].

Past earthquake disasters have indicated that lack of science, good governance, illiteracy, poverty, corruption, and scientifically unaware societies are the major contributors for such disaster vulnerabilities. It thus clearly suggests that one must work hard to curb all these major factors to efficiently counter the earthquake disasters in future.

Malaysia, like many other developing nations, ought to build a strong earthquake science foundation, and develop a comprehensive plan to investigate all the faults that may be cause of concern in the coming future. At the same time, education and awareness planning are required to thoroughly inform people about the potential problems related to earthquake hazards.

About the Author

Dr. Afroz Ahmad Shah is an experienced geoscientist with key experience in understanding the regional tectonics, fault mapping, metamorphic petrology, micro-tectonics, structural geology, analysis and interpretation of seismic, 3D seismic exploration, bathymetry, geodetic, and geological data, resource management and information technology. He is currently an Assistant Professor of Structural Geology at the Faculty of Science, Department of Geoscience, Universiti Brunei Darussalam. Prior to this, he was a Senior Lecture of Structural Geology at Curtin University, Sarawak, where his research work was mainly on faults and how tectonic forces have structured the formation of the Sarawak Basin and its hydrocarbon potential. Check out Dr. Afroz’s Scientific Malaysian profile at http://www.scientificmalaysian.com/members/afrozshah/.

This article first appeared in the Scientific Malaysian Magazine Issue 11. Check out other articles in Issue 11 by downloading the PDF version for free here: Scientific Malaysian Magazine Issue 11 (PDF version)

References

[1] Hutchison, C.S., 2005. Geology of North-West Borneo, Elsevier B.V., 421pp.

[2] Sabah quake: Death toll rises to 18; Malaysia to end search and rescue ops”. The Straits Times. 10 June 2015. Retrieved 10 June 2015. http://www.straitstimes.com/news/asia/south-east-asia/story/sabah-quake-death-toll-rises-18-after-missing-singaporeans-found-201

[3] Sapin, F., Hermawan, I., Pubellier, M., Vigny, C., & Ringenbach, J. C. (2013). The recent convergence on the NW Borneo Wedge—a crustal-scale gravity gliding evidenced from GPS. Geophysical Journal International, 193(2), 549-556.

[4] Morley, C.K., 2009. Growth of folds in deep-water setting, Geopshere, 5, 59–89.

[5] Cullen, A., 2010. Transverse segmentation of the Baram-Balabac Basin,NW Borneo: refining the model of Borneo’s tectonic evolution, Pet. Geosci., 16, 3–19.

[6] King, R.C., Back´e, G., Morley, C.K., Hillis, R.R. & Tingay, M.R.P., 2010a. Balancing deformation in NW Borneo: quantifying plate-scale vs. gravitational tectonics in a delta and deepwater fold-thrust belt system, Mar. Pet. Geol., 27, 238–249.

[7] King, R.C., Hillis, R.R., Tingay, M.R.P. & Damit, A.-R., 2010b. Presentday stress and neotectonic provinces of the Baram Delta and deep-water fold-thrust belt, J. Geol. Soc., 166, 197–200.

[8] Hesse, S., Back, S. & Franke, D., 2009. The deep-water fold-and-thrust belt offshore NW Borneo: gravity-driven versus basement-driven shortening, Bull. Geol. Soc. Am., 121, 939–953.

[9] Sandal, S.T., 1996. The Geology and Hydrocarbon Resources of Negara Brunei Darussalam, Brun. Shell Pet., Bandar Seri Begawan, 243pp.

[10] Hough, S. 2009. Predicting the unpredictable: the tumultuous science of earthquake prediction. Princeton University Press.

[11] Shah, A. (2014). Predicting the Unpredictable: The Tumultuous Science of Earthquake Prediction: review. Geosciences Journal, 3(18), 373-374.

[12] Mugnier, J. L., Gajurel, A., Huyghe, P., Jayangondaperumal, R., Jouanne, F., & Upreti, B. (2013). Structural interpretation of the great earthquakes of the last millennium in the central Himalaya. Earth-Science Reviews, 127, 30-47.

[13] Bilham, R. and V. Gaur., Buildings as Weapons of Mass Destruction: Earthquake risk in South Asia, Science, 2013, 341, 618-619

[14] Ambraseys, N and Bilham, R. 2011. Corruption Kills, Nature 469, 143-145.



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