ALBERT

Description: The September 2022 Hurricane Ian, which made a landfall as a Category four hurricane, with wind speeds reaching 240 km/h, was among the most destructive hurricanes to hit Florida: at least 77 deaths were reported in Florida and North Carolina, and the total damage was estimated to approximately US$ 63 billion. Along the coast Hurricane Ian generated both a normal (positive) and a reverse (negative) storm surge. A comprehensive data analysis and modelling efforts were undertaken to illuminate processes leading to two types of surges. Mean sea level pressure and wind data from 49 meteorological NOAA and ASOS stations, measured with 1-6 min time step, along with sea level data from 11 NOAA tide gauges, measured with a 1 min time step, were analysed. The ERA5 Reanalysis data were used to assess propagation parameters and synoptic scale properties of Hurricane Ian. Numerical weather prediction High-Resolution Rapid Refresh (HRRR) model, and a parametric wind model of tropical cyclones were both used to estimate temporal evolution of the 10 m wind and mean sea level pressure fields near and over Florida. The models were then used separately to force the Regional Ocean Modelling System (ROMS), and to reproduce positive and negative surges. Differences between two sets of simulations are discussed in detail. It was shown that the main factor governing appearance of positive and negative surge was high spatial changeability of wind field over a relatively small (O(200 km)) area.

Description: The destructive tsunami on 22 December 2018 due to the flank collapse of the Anak Krakatau volcano was a bitter reminder of large tsunami risks and of the shortcomings of the existing tsunami warning systems for atypical (non-seismic) sources. In the Mediterranean, several tsunamis were generated by landslides associated with volcanic systems in the past.The volcanic unrest experienced in 2011-2012 on the Santorini volcanic island in the Southern Aegean Sea pointed out the need to identify and quantify tsunami hazard and risk due to possible flank instability which may be triggered as a result of volcanic unrest or nearby seismotectonic activities. Inspired from this need, in this study we examined three possible landslide scenarios in Santorini Island with tsunamigenic potential. The results show that the scenarios considered in our study are able to generate significant local tsunamis impacting Santorini and the nearby islands, as well as producing significant impact along the coasts of the Southern Aegean Sea. While maximum tsunami amplitudes/arrival time ranges are 1.2m/30-90min for locations in the Greek-Turkish coasts in the far field, they are in the order of ≈60m/1-2min for some locations at the Santorini Island. The extreme tsunami amplitudes and short arrival times for locations inside the Santorini Island is a major challenge in terms of tsunami hazard warning and mitigation. As an effort to address this challenge, a discussion on the requirements for local tsunami warning system addressing atypical sources in the context of multi-hazard disaster risk reduction is also provided.

Description: Eastern Indonesia suffers from significant tsunami hazards due to its complex tectonic setting characterized by several subduction zones, numerous active volcanoes, as well as submarine landslides. Following the two destructive tsunamis in Indonesia in 2018 in Palu and Sunda Strait, it has been urgent to address large tsunami hazards in this unique tsunamigenic zone. This presentation outlines the outcomes of an international collaborative project on “Building Earthquake and Tsunami Resilience in East Indonesia”, supported by the Royal Society (UK) for the period 2019-2023. The project brought together research teams from UK and Indonesia, working together towards safer communities from tsunamis and earthquakes. The project mapped and studied seismogenic and tsunamigenic zones in East Indonesia, modelled scenarios of potential future tsunamis, and developed community resilience to tsunamis. A marine seismic survey was conducted in August 2022 to obtain seismic and bathymetric data from the region. The project also studied several recent earthquakes and tsunamis in the region, including the 14th November 2019 Molucca Sea tsunami following an Mw 7.2 earthquake, the 16th of June 2021 tsunami following an Mw 5.9 earthquake, and the 2018 Palu earthquake and tsunamis. It is believed that this project has generated a large database for earthquake and tsunami resilience studies in East Indonesia, and will inspire future research works. This research is funded by The Royal Society (the United Kingdom), grant number CHL/R1/180173 and Lloyd’s Tercentenary Research Foundation, the Lighthill Risk Network, and the Lloyd’s Register Foundation.

Description: Two large earthquakes occurred in the Alaska-Aleutian subduction zone in July 2020 (Mw 7.8) and July 2021 (Mw 8.2), generating tsunamis characterized by considerably longer periods than that typically expected from their moment magnitudes. The 2020 earthquake resulted in approximately 40–90 min tsunami periods (Mulia et al., 2022, GRL; Heidarzadeh and Mulia, 2021, Ocean Eng.). Similarly, the 2021 event exhibited long-period tsunamis of 〉50 min (Mulia et al., 2022, SRL). For comparison, the April 2014 Illapel, Chile, earthquake (Mw 8.2) and the November 2016 Kaikoura, New Zealand, earthquake (Mw 7.8) produced tsunamis with dominant periods ranging from 15 to 21 min (Heidarzadeh et al., 2019, Ocean Eng.). To reveal the underlying cause for such anomalous occurrences, we conducted an inversion analysis using tsunami and geodetic data. Our inversion results indicated the up-dip extent of both earthquakes confined at a depth of ~20 km of the plate interface, which corresponds to the shelf break on the surface. Therefore, the coseismic surface displacement predominantly took place at shallow water depths of ~200 m within the broad continental shelf extending ~120 km offshore. Consequently, it is responsible for the long-period tsunami waves as the water depth is inversely proportional to the period. This geophysical setting is uniquely attributed to the Alaska-Aleutian subduction zone, which is rarely found in other major subduction systems. References: https://doi.org/10.1029/2021GL094937; https://doi.org/10.1785/0220210359; https://doi.org/10.1016/j.oceaneng.2021.109243.