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Earthquake geology of Southeast Asia

In many parts of the world, active faults are too poorly understood to allow even rudimentary quantification of their role in regional neotectonic deformation or to make realistic estimates of seismic hazards, let alone seismic risk assessments.Such was the case before the infamous 1999 Chi-Chi earthquake in Taiwan. That rather late awakening in Taiwan to the value of using tectonic landforms in the characterization of active faults and folds led to the systematic application of geomorphic evidence to characterize the active tectonics throughout the island and offshore, which was carried out by J. Bruce H. Shyu (National Taiwan University, Taipei, Taiwan) and his group. Although the active fault that produced the earthquake had long been known from the interpretation of subsurface (stratum below the earth’s surface) data and outcrops (group of rocks that stick out of the ground), it had not been considered active. Surface fault ruptures and associated folding during the earthquake clearly revealed the fault’s location, danger and clear geomorphic evidence for recent, prior activity. A similar geomorphological investigation of the neotectonic elements of Myanmar is largely completed, as part of the Ph.D. work of Caltech graduate student Wang Yu.

The situation in western Indonesia after the 2004 Indian Ocean earthquake and tsunami illustrates well the state of SEAsian neotectonics. Soon after the devastating earthquake and tsunami of 2004, when theUnited States Geological Survey(USGS)was producing a Probabilistic Seismic Hazard Analysis (PSHA) of the western half of Indonesia,survey personnel found that there was little in the way of reliable active-fault mapping. We, at the Earth Observatory of Singapore,were asked to rapidly compile a map of the active faults of Sumatra, Java, Borneo and Bali to serve as a key element in their evaluation of probabilistic earthquake hazard. We spent a couple of months evaluating Shuttle Radar Topography Mission (SRTM) digital imagery and presented them with a very crude map of active structures, which they used in their analysis.  

The active tectonic elements of many other regions within SE Asia are also not well understood. These include eastern Indonesia, Malaysia, Laos, Vietnam, Cambodia and many offshore tracts. Likewise, rates of fault slip and past seismic history are for the most part poorly known. This regional state-of-knowledge contrasts markedly with better-studied places such as Japan and California. More than two decades ago, earlier thorough mapping of active structures enabled creation of the first probabilistic seismic hazard maps of those places. The fact that nearly all of the dozen or so subsequent destructive earthquakes in California have occurred within the high-probability areas shown by the California maps attests to the reliability of these early PSHA maps. More recent PSHA maps covering the entirety of the US are the basis for today’s seismic zonation of the country. These maps, too, are based upon knowledge of the location of active faults and varying levels of understanding of their slip rates.

The Earth Observatory of Singapore was established in 2009 to fill the above-mentioned gaps in research and the aim is “to conduct fundamental research on earthquakes, volcanic eruptions, tsunami and climate change in and around SE Asia, toward safer and more sustainable societies”.It has successfully conducted research in most of the SE Asia. However, to the best of our knowledge, there has not been involvement of any scientist from Malaysia to conduct the earthquake research. We are aware that the need to undertake a thorough research study on earthquakes is more in Malaysia than in Singapore, potentially because of the tectonic settings and the dimensions of the country . This has not been done in any part of the country and therefore, it is extremely important to map all the active tectonic features in Malaysia.By observing the satellite images, many places in Malaysia with active faults should be mapped in greater detail, so that we can understand the potential of earthquake risk in the country and surrounding areas in the future. Also, the potential earthquake risk from the neighbouring regions (e.g. Indonesia) should be assessed. There are various seismic sources around this country (Figure 1, upper panel), which are partially mapped and based on these structures,the USGS has produced a generalised earthquake hazard map of the region (Figure 1, lower panel). Though it should be noted that this map is crude and therefore, it is compulsory to conduct a thorough research on risk of earthquakes in order to generate a more realistic earthquake hazard map of the region. Also, the paleoseismic (old earthquakes) research is required to understand the past earthquakes and their sources.


Figure 1: The tectonic setting (upper panel) and generalized seismic hazard (lower panel) of Malaysia and its surrounding areas

As a conclusion, the earth sciences education is extremely important to minimize the risks associated with natural hazards. Unfortunately,Malaysian higher education institutions do not offer a comprehensive geosciences degree program. To fill these obvious gaps, both in education and research, will require serious collaborations with earth scientists around the globe and therefore, we would be happy to work with any of the experts in Malaysia to spread the earth sciences awareness in this country.

Scientific Malaysian Profile:
http://www.scientificmalaysian.com/scimy/members/afrozshah/profile/  

Link:
TEDxNTU talk by Dr Afroz Ahmad Shah – Is earthquake prediction a possibility?