The tsunami and cyclone hazard in Myanmar - Surveying coastal geoarchives for sedimentary evidence of extreme wave events

至少自2004年印度洋海啸(IOT)以来，地质海啸证据的益处是确凿无疑的。尽管2004年物联网的规模也非常大，但其灾难性影响只能通过对该地区海啸风险的认识不足来解释。作为仪器和历史记录中第一次这方面的海啸，只有地质证据才能提供关于以前发生的事件的信息，以提高认识并触发减少脆弱性的措施。这个例子以及2008年缅甸热带气旋纳尔吉斯或菲律宾2013年超级台风海燕之后的类似观测表明，可靠的危险评估必须建立在长期发生不同强度的极端波浪事件的基础上。虽然东南亚现代和历史的热带气旋和海啸的频率震级信息仅限于几个世纪，但地质印记可能覆盖数千年的周期，并以异常大小和低频率记录母羊。尽管2004年物联网在大多数受影响的地区引发了密集的研究，但对缅甸的母羊矿床仍然知之甚少。因此，异常热带气旋和海啸造成的长期危害很难控制，尽管缅甸面临三个主要来源的沿海洪水：(1)孟加拉湾产生的热带气旋东移(如TC Nargis)；(2)由舜达弧北-苏门答腊岛-安达曼段完全破裂引发的海啸(例如，2004年IOT)；(3)缅甸西部沿海若开河(若干)段破裂引发的海啸(例如1762年海啸)。由于缺乏调查至少部分是由于缅甸在过去几十年的政治孤立导致的有限研究活动的结果，我们假设在合适的近岸地理档案中存在EWE的地质证据；这些有助于更好地了解长期的海啸和龙卷风危险。虽然拟议的研究的先决条件是仰光和科隆大学之间的合作，但由于保存较差或稀有的EWE矿藏的可能性建议对几个地点进行调查，而不是对个别地点进行系统调查。因此，缅甸沿海的6-8个滩脊平原应使用轻型设备进行测量，以便对绵羊地貌(风暴脊、洗地扇)和沙层进行平整(DGPS)和取样(壕沟、推芯)。结合沉积学(粒度、动物群、矿物学、地球化学)和年代学(放射性碳、光激发发光)实验室分析，拟议的调查应通过以下方式触发后续项目：(1)为有希望的地点提供系统调查的基础；(2)向参加实地调查的当地毕业生传授知识。

Since at least the 2004 Indian Ocean Tsunami (IOT) the benefits of geological tsunami evidence are well established. Although the IOT 2004 also had an exceptional magnitude, its catastrophic effects can only be explained by missing awareness concerning the tsunami risk of the region. Being the first tsunami of this dimension on instrumental and historical records, only geological evidence could have provided information on predecessor events to raise awareness and trigger vulnerability-reducing measures. This example and similar observations after tropical cyclone (TC) Nargis 2008 in Myanmar or Supertyphoon Haiyan 2013 in the Philippines demonstrate that robust hazard assessment must be based on the occurrence of extreme wave events (EWE) with different magnitudes over a prolonged time. While frequency-magnitude information from modern and historical TCs and tsunamis in SE Asia is restricted to a few centuries, geological imprints potentially cover periods of several millennia and record EWE with exceptional magnitudes and low frequencies.While the IOT 2004 triggered intensive research in most affected areas, still very little is known about EWE deposits in Myanmar. In consequence, the long-term hazard due to exceptional TCs and tsunamis is poorly constrained, although Myanmar is exposed to coastal flooding from three major sources: (i) eastward-moving TCs generated in the Bay of Bengal (e.g. TC Nargis); (ii) tsunamis triggered by complete ruptures of the North-Sumatra-Andaman segment of the Sunda Arc (e.g. the IOT 2004); and (iii) tsunamis triggered by ruptures of the Rakhine (Arakan) segment offshore western Myanmar (e.g. the 1762 tsunami). Since the lack of investigations is at least partly the result of a limited research activity due to the political isolation of Myanmar during the last decades, we assume that geological evidence of EWE is present in suitable near-shore geoarchives; these can contribute to an improved understanding of the long-term tsunami and cyclone hazard.While the preconditions for the proposed research are provided by a cooperation between Yangon and Cologne Universities, the possibility of poorly preserved or scarce EWE deposits advises a survey of several sites rather than a systematic investigation of individual locations. Therefore, 6-8 beach-ridge plains along the coasts of Myanmar shall be surveyed using light equipment for levelling (DGPS) and sampling (trenches, push cores) of EWE landforms (storm ridges, washover fans) and sand sheets. In combination with sedimentological (granulometry, fauna, mineralogy, geochemistry) and chronological (radiocarbon, optically stimulated luminescence) laboratory analyses the proposed survey shall trigger follow-up projects by (i) providing a basis for the systematic investigation of promising sites; and (ii) transferring knowledge to local graduates that participate in the field survey.