Efficient Methods for Site-Specific Probabilistic Tsunami Hazard Analysis

Date: 4/25/2019

Time: 11:00 AM

Room: Cascade II

Probabilistic Tsunami Hazard Analysis is a computationally intensive process due to the use of numerical methods to compute source excitation and wave propagation, because significant sources may be thousands of miles away from the target site, resulting in a very large computational domain. For site-specific studies, the cost of such a procedure might be prohibitive. To solve this problem, we have developed an efficient method for site-specific offshore Probabilistic Tsunami Hazard Analysis (PTHA) using reciprocal Green’s functions. Reciprocity, where a basin-wide tsunami response to an uplift event at the site is computed, allows us to compute tsunami Green’s functions from seafloor uplift over a very wide area using a single finite-difference run (in principle) which also gives us great flexibility in terms of source geometry. This approach even allows us to compute the hazard from submarine landslide sources, as well as combined hazard from landslides and earthquakes, and thus provides a computational framework for a comprehensive tsunami hazard analysis.

We have applied this method to two test-cases for site-specific tsunami hazard analysis, one near Cook Strait, New Zealand and one along the Sunda Arc. This methodology allows us to compute the hazard from a range of sources including more unusual or infrequent ones like tsunami earthquakes and submarine landslides in a single framework. For the Sunda Arc, the occurrence of tsunami earthquakes, events that produce a larger tsunami than would be expected for their magnitude, the flexibility of using seafloor uplift as basis for the Green's functions enables us to explore a wider range of potential mechanical models that could explain their anomalous character. For the Cook Strait area, an existing probabilistic model for submarine landslides is used in addition to a more traditional earthquake recurrence model, and preliminary results show that submarine landslides may become a significant contributor to the local tsunami hazard for relatively short (2500 year) return periods.

Presenting Author: Hong Kie Thio

Authors