Historical Tsunamis of Taiwan in the Eighteenth Century: the 1781 Jiateng Harbor Flooding and 1782 Tsunami Event

This research aims to study two of the historical tsunamis occurred in Taiwan during the 18th century and to reconstruct the incidents. The 1781 Jiateng Harbor Flooding, recorded by the Chinese historical document, Taiwan Interview Catalogue, took place on the southwest coast of Taiwan. On the other hand, the 1782 Tsunami was documented in foreign languages, with uncertainties of the actual time. Reasoning these historical events requires not only carefully examining the literature records but also performing the scenarios that match the descriptions. The Impact Intensity Analysis (IIA) is employed to locate possible regions of tsunami sources in order to reproduce the events. Numerical simulations based on the Cornell Multi-Grid Coupled Tsunami Model (COMCOT) analyze the influence of different types of tsunami generated both by submarine mass failures and seismic activities. Numerical results indicate that the source of the 1781 Jiateng Harbor Flooding is located very possibly at the South South-West side of Taiwan. However, simulation results and historical records put the existence of the 1782 Tsunami in doubt, and the possibility of storm surges could not be ruled out.

Analysis of the tsunami amplification effect by resonance in Yeongil Bay

Predicting tsunami hazards based on the tsunami source, propagation, runup patterns is critical to protect humans and property. Potential tsunami zone, as well as the historical tsunamis in 1983 and 1993, can be a threat to the east coast of South Korea. The Korea Meteorological Administration established a tsunami forecast warning system to reduce damage from tsunamis, but it does not consider tsunami amplification in the bay due to resonance. In this study, the Numerical model, Cornell Multi-grid Coupled Tsunami model, was used to investigate natural frequency in the bay due to coastal geometry. The study area is Yeongill bay in Pohang, southeast of South Korea, because this area is a natural bay and includes three harbors where resonance significantly occurs. This study generated a Gaussian-shaped tsunami, propagated it into the Yeongill bay, and compared numerical modeling results with data from tide gauge located in Yeongill bay during several storms through spectral analysis. It was found that both energies of tsunamis and storms were amplified at the same frequencies, and maximum tsunami wave height was amplified about 3.12 times. The results in this study can contribute to quantifying the amplification of tsunami heights in the bay.

GIS Based Tsunami Risk Assessment

Tsunami is a coastal hazard which occur due to undersea earthquakes, Meteorite falls, volcanic eruptions or even nuclear weapon operations. The tsunami hazard which occurred in December 2004 was generated due to an undersea earthquake 400m west of northern Sumatra and it inundated coastal areas of Indonesia, Sri Lanka, Thailand and India. This hazard became one of the worst disasters in the history resulting in over thirty thousand fatalities and over seventy thousand house damage in Sri Lanka. This study is focused towards creation of GIS based Tsunami risk map for Galle city which was badly hit by the 2004 Tsunami. Tsunami vulnerability was assessed using weighted overlay spatial method with input parameters of population density, sex ratio, age ratio, disability ratio and damaged building ratio. Tsunami hazard map was developed based on tsunami inundation map which was published by Coastal research and design, costal conservation and resource management department with assistant from Disaster management centre using the Cornell Multigrid Coupled Tsunami Model (COMCOT). Vulnerable and hazard maps were analysed and incorporated to develop final risk map using GIS tool. Keywords GIS; Tsunami Inundation Map; Tsunami Risk Map; Vulnerability; Disaster

Anatomy of strike-slip fault tsunami genesis

Tsunami generation from earthquake-induced seafloor deformations has long been recognized as a major hazard to coastal areas. Strike-slip faulting has generally been considered insufficient for triggering large tsunamis, except through the generation of submarine landslides. Herein, we demonstrate that ground motions due to strike-slip earthquakes can contribute to the generation of large tsunamis (>1 m), under rather generic conditions. To this end, we developed a computational framework that integrates models for earthquake rupture dynamics with models of tsunami generation and propagation. The three-dimensional time-dependent vertical and horizontal ground motions from spontaneous dynamic rupture models are used to drive boundary motions in the tsunami model. Our results suggest that supershear ruptures propagating along strike-slip faults, traversing narrow and shallow bays, are prime candidates for tsunami generation. We show that dynamic focusing and the large horizontal displacements, characteristic of strike-slip earthquakes on long faults, are critical drivers for the tsunami hazard. These findings point to intrinsic mechanisms for sizable tsunami generation by strike-slip faulting, which do not require complex seismic sources, landslides, or complicated bathymetry. Furthermore, our model identifies three distinct phases in the tsunamic motion, an instantaneous dynamic phase, a lagging coseismic phase, and a postseismic phase, each of which may affect coastal areas differently. We conclude that near-source tsunami hazards and risk from strike-slip faulting need to be re-evaluated.

The 2018 Palu Tsunami: Coeval Landslide and Coseismic Sources

On 28 September 2018, Indonesia was struck by an MW 7.5 strike-slip earthquake. An unexpected tsunami followed, inundating nearby coastlines leading to extensive damage. Given the traditionally non-tsunamigenic mechanism, it is important to ascertain if the source of the tsunami is indeed from coseismic deformation, or something else, such as shaking induced landsliding. Here we determine the leading cause of the tsunami is a complex combination of both. We constrain the coseismic slip from the earthquake using static offsets from geodetic observations and validate the resultant “coseismic-only” tsunami to observations from tide gauge and survey data. This model alone, although fitting some localized run-up measurements, overall fails to reproduce both the timing and scale of the tsunami. We also model coastal collapses identified through rapidly acquired satellite imagery and video footage as well as explore the possibility of submarine landsliding using tsunami raytracing. The tsunami model results from the landslide sources, in conjunction with the coseismic-generated tsunami, show a greatly improved fit to both tide gauge and field survey data. Our results highlight a case of a damaging tsunami the source of which is a complex mix of coseismic deformation and landsliding. Tsunamis of this nature are difficult to provide warning for and are underrepresented in regional tsunami hazard analysis.

Coordinated efforts in tsunami hazard and risk analyses in Europe and link to the Global Tsunami Model network initiative

<p>The tsunami disasters of 2004 in the Indian Ocean and of 2011 along the Tohoku coast of Japan revealed severe gaps between the anticipated risk and consequences, with resulting loss of life and property. A similar observation is also relevant for the smaller, yet disastrous, tsunamis with unusual source characteristics such as the recent events in Palu Bay and Sunda Strait in 2018. The severe consequences were underestimated in part due to the lack of rigorous and accepted hazard analysis methods and large uncertainty in forecasting the tsunami sources. Population response to small recent tsunamis in the Mediterranean also revealed a lack of preparedness and awareness. While there is no absolute protection against large tsunamis, a more accurate analysis of the potential risk can help to minimize losses. The tsunami community has made significant progress in understanding tsunami hazard from seismic sources. However, this is only part of the inputs needed to effectively manage tsunami risk, which should be understood more holistically, including non-seismic sources, vulnerability in different dimensions and the overall societal effects, in addition to its interaction with other hazards and cascading effects. Moreover, higher standards need to be achieved to manage and quantify uncertainty, which govern our basis for tsunami risk decision making. Hence, a collective community effort is needed to effectively handle all these challenges across disciplines and trades, from researchers to stakeholders. To coordinate and streamline these activities and make progress towards implementing the Sendai Framework of Disaster Risk Reduction (SFDRR) the Global Tsunami Model network (GTM) was initiated in 2015 towards enhancing our understanding of tsunami hazard and risk from a local to global scale. Here, we focus on coordinated European efforts, sharing the same goals as GTM, towards improving standards and best practices for tsunami risk reduction. The networking initiative, AGITHAR (Accelerating Global science In Tsunami HAzard and Risk Analysis), is a European COST Action, aims to assess, benchmark, improve, and document methods to analyse tsunami hazard and risk, understand and communicate the uncertainty involved, and interact with stakeholders in order to understand the societal needs and thus contribute to their effort to minimize losses. In this presentation, we provide an overview of the suite of methodologies used for tsunami hazard and risk analysis, review state of the art in global tsunami hazard and risk analysis, dating back to results from the Global Risk Model in 2015, and highlight possible gaps and challenges. We further discuss how AGITHAR and GTM will address how to tackle these challenges, and finally, discuss how global and regional structures such as the European Plate Observing System (EPOS) and the UNDRR Global Risk Assessment Framework (GRAF) can facilitate and mutually benefit towards an integrated framework of services aiding improved understanding of multiple hazards.</p>

Identifikasi Pendekatan Shallow Water Equation Dalam Simulasi 2D Gelombang Tsunami di Pantai Keburuhan Purworejo

Kabupaten Purworejo merupakan salah satu dari lima daerah yang terkena dampak run-up tsunami Jawa 17 Juli 2006. Berdasarkan hasil Rapid Survey oleh BPDP dan BPPT, sepanjang Pantai Keburuhan merupakan lokasi terjadinya run-up tsunami di Kabupaten Purworejo di koordinat 109.912 LS -7.85 BT sebesar 1,7 meter. Tujuan dari penelitian ini adalah memperkirakan waktu tempuh tsunami, distribusi tinggi gelombang tsunami dan daerah jangkauan tsunami akibat dampak gempa tsunami Jawa 17 Juli 2006 di Pantai Keburuhan, Purworejo. Metode yang digunakan adalah metode deskriptif analitis dengan pendekatan kuantitatif. Data yang digunakan pada penelitian ini adalah titik tinggi, batimetri, parameter gempa, peramalan pasang surut wilayah perairan Pantai Keburuhan, data citra Geo Eye 1, dan kelerengan pantai. Pemodelan tsunami menggunakan perangkat lunak COMCOT v1.7 dengan kejadian gempa Jawa 17 Juli 2006. Berdasarkan pengolahan data, diketahui bahwa kecepatan gelombang maksimal sebesar 3.8788 m/s. Pada menit ke- 40, amplitudo awal gelombang tsunami sebesar 1.644 meter telah mencapai Pantai Keburuhan. Daerah jangkauan tsunami terluas dan jarak jangkauan maksimum terjauh terjadi di Pantai Keburuhan adalah 1,23 km2 dan 1,4 km. Berdasarkan hasil verifikasi dengan nilai RSR sebesar 0,26. Hasil validasi simulasi tsunami menggunakan COMCOT v1.7 diketahui bahwa tinggi run-up tsunami model sudah cukup sesuai dengan data run-up yang terjadi saat kejadian, dengan nilai RSR sebesar 0,29 dan CF sebesar 1,63.