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IHRR Seminar: Insights into the largest earthquakes and tsunamis: the role of coastal sediments
Megathrust earthquakes, the largest fault ruptures occurring along subduction zones, generate intense long-duration shaking and trigger tsunamis. Together, earthquakes and tsunamis pose major hazards for many regions around the world. Since 2004, at least 40 tsunamis have together killed more than 250,000 people and caused financial losses exceeding $250 billion. With in excess of 10 % of the global population living in coastal areas at elevations below 10 m and sea-level rise accentuating the impact of extreme waves in many regions, the need for comprehensive, detailed and geologically-grounded coastal hazard assessments has never been greater.
Seismic and tsunami hazard assessments attempt to quantify future hazards; nevertheless, incomplete understanding of the magnitude and frequency of the largest events has resulted in failures in the anticipation of disasters such as the 2004 Sumatra-Andaman and 2011 Tōhoku earthquakes and tsunamis. These events were substantially larger than recent instrumentally or historically documented earthquakes along their respective faults. The long recurrence intervals between the largest events and the reliance on short and incomplete records to inform hazard assessments thwarted appropriate mitigation efforts. Palaeoseismology, the use of geological records to understand past fault behaviour, can provide a longer perspective on earthquake and tsunami hazards. In this seminar I will discuss how coastal sediments may preserve records of earthquake and tsunami occurrence over thousands of years. Describing a range of approaches, illustrated by examples from my work in Chile, Japan and Alaska, I will describe how these coastal archives can be used to provide insights into earthquake magnitude, the occurrence of tsunamis and the recurrence intervals between the largest events.
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