Monitoring and Modelling of ionospheric disturbances by means of GRACE, GOCE and Swarm in-situ observations

<p>The main objective of the ESA-funded project COSTO (Contribution of Swarm data to the prompt detection of Tsunamis and other natural hazards) is to better characterize, understand and discover coupling processes and interactions between the ionosphere, the lower atmosphere and the Earth’s surface as well as sea level vertical displacements. Together with our project partners from the University of Warmia and Mazury (UWM), the National Observatory of Athens (NOA) and the Universitat Politecnica de Catalunya (UPC) we focus in COSTO to tsunamis that are the result of earthquakes (EQ), volcano eruptions or landslides.</p><p>In the scope of COSTO a roadmap was developed to detect the vertical and horizontal propagation of Travelling Ionospheric Disturbances (TID) in the observations of Low Earth Orbiting (LEO) satellites. Under the assumption that the TIDs triggered by tsunamis behave in approximately the same way for different EQ / tsunami events, this roadmap can be applied also to other events. In this regard, the Tohoku-Oki EQ in 2011 and the Chile EQ in 2015 were studied in detail. The aim of investigating these events is to detect the TIDs in the near vicinity of the propagating tsunami. Thereby, given tsunami propagation models serve as a rough orientation to determine the moments in time and positions for which there is co-location with selected LEO satellites/missions, namely GRACE, GOCE and Swarm. GOCE with an altitude of around 280km and the GRACE satellites with an altitude of around 450km flew over the region where the Tohoku-Oki tsunami was located, about 2.5 hours after the EQ. Using wavelet transform, similar signatures with periods of 10-30 seconds could be detected in the top-side STEC observations of GOCE as well as in the Ka-band observations of GRACE at the time of the overflight. These signatures can be related to the gravity wave originating from the tsunami. Similar signatures were detected in the signals from the GRACE Ka-band observations and in the Swarm Langmuir Probe measurements at an altitude of 450 km for the 2015 Chile tsunami. These roadmap studies provided the first opportunity to observe the vertical and horizontal tsunami induced gravity waves in the ionosphere.</p>

Speeding up and boosting tsunami warning in Chile

Chile host a great tsunamigenic potential along its coast, even with the large earthquakes occurred during the last decade, there is still a large amount of seismic energy to release. This permanent feature and the fact that the distance between the trench and the coast is just 100 km creates a difficult environment to do real time tsunami forecast. In Chile tsunami warnings are based on reports of the seismic events (hypocenter and magnitude) and a database of precomputed tsunami scenarios. However, because yet there is no answer to image the finite fault model within first minutes (before the first tsunami wave arrival), the precomputed scenarios consider uniform slip distributions. Here, we propose a scheme of processes to fill the gaps in-between blind zones due to waiting of demanding computational stages. The linear shallow water equations are solved to obtain a rapid estimation of the run-up distribution in the near field. Our results show that this linear method captures most of the complexity of the run-up heights in terms of shape and amplitude when compared with a fully non-linear tsunami code. Also, the run-up distribution is obtained in quasi real-time as soon as the seismic finite fault model is produced.

Development and application of a tsunami fragility curve of the 2015 tsunami in Coquimbo, Chile

The last earthquake that affected the city of Coquimbo took place in September 2015 and had a magnitude of Mw=8.3, resulting in localized damage in low-lying areas of the city. In addition, another seismic gap north of the 2015 earthquake rupture area has been identified; therefore, a significant earthquake (Mw=8.2 to 8.5) and tsunami could occur in the near future. The present paper develops a tsunami fragility curve for the city of Coquimbo based on field survey data and tsunami numerical simulations. The inundation depth of the 2015 Chile tsunami in Coquimbo was estimated by means of numerical simulation with the Non-hydrostatic Evolution of Ocean WAVEs (NEOWAVE) model and five nested grids with a maximum grid resolution of 10 m. The fragility curve exhibited behavior similar to that of other curves in flat areas in Japan, where little damage was observed at relatively high inundation depths. In addition, it was observed that Coquimbo experienced less damage than Dichato (Chile); in fact, at an inundation depth of 2 m, Dichato had a ∼75 % probability of damage, while Coquimbo proved to have only a 20 % probability. The new fragility curve was used to estimate the damage by possible future tsunamis in the area. The damage assessment showed that ∼50 % of the structures in the low-lying area of Coquimbo have a high probability of damage in the case of a tsunami generated off the coast of the study area if the city is rebuilt with the same types of structures.

Tsunami fragility curve using field data and numerical simulation of the 2015 tsunami in Coquimbo, Chile

The last earthquake which affected Coquimbo city took place in September 2015, with localized damage observed in low areas of the city. In addition, another seismic gap north of the 2015 earthquake rupture area has been identified; therefore, a significant earthquake and tsunami could occur in the near future. The present paper develops the tsunami fragility curve for the city of Coquimbo based on field survey data and tsunami numerical simulations. The inundation depth of the 2015 Chile tsunami in Coquimbo was estimated by means of numerical simulation with the NEOWAVE model and 5 nested grids with a maximum grid resolution of 10 m. The fragility curve exhibited behavior similar to that of other curves in plain areas in Japan, where low damage was observed at relatively high inundation depths. The new fragility curve was used to estimate the damage by possible future tsunamis in the area. The damage assessment showed that ~ 50 % of the structures in the lower area of Coquimbo have a high probability of damage in case of a tsunami generated off the coast of the study area if the city is rebuilt with the same type of structures.

Risk factors and perceived restoration in a town destroyed by the 2010 Chile tsunami

A large earthquake and tsunami took place in February 2010, affecting a significant part of the Chilean coast (Maule earthquake, Mw of 8.8). Dichato (37° S), a small town located on Coliumo Bay, was one of the most devastated coastal areas and is currently under reconstruction. Therefore, the objective of this research is to analyze the risk factors that explain the disaster in 2010, as well as perceived restoration 6 years after the event. Numerical modeling of the 2010 Chile tsunami with four nested grids was applied to estimate the hazard. Physical, socioeconomic and educational dimensions of vulnerability were analyzed for pre- and post-disaster conditions. A perceived restoration study was performed to assess the effects of reconstruction on the community. It was focused on exploring the capacity of newly reconstructed neighborhoods to provide restorative experiences in case of disaster. The study was undertaken using the perceived restorativeness scale. The vulnerability variables that best explained the extent of the disaster were housing conditions, low household incomes and limited knowledge about tsunami events, which conditioned inadequate reactions to the emergency. These variables still constitute the same risks as a result of the reconstruction process, establishing that the occurrence of a similar event would result in a similar degree of devastation. For post-earthquake conditions, it was determined that all neighborhoods have the potential to be restorative environments soon after a tsunami. However, some neighborhoods are still located in areas devastated by the 2010 tsunami and again present high vulnerability to future tsunamis.