Tsunami generation of the 1993 Hokkaido Nansei-Oki earthquake

Heterogeneous fault motion of the 1993 Hokkaido Nansei-Oki earthquake is studied by using seismic, geodetic and tsunami data, and the tsunami generation from the fault model is examined. Seismological analyses indicate that the focal mechanism of the first 10 s, when about a third of the total moment was released, is different from the overall focal mechanism. A joint inversion of geodetic data on Okushiri Island and the tide gauge records in Japan and Korea indicates that the largest slip, about 6 m, occurred in a small area just south of the epicenter. This corresponds to the initial rupture on a fault plane dipping shallowly to the west. The slip on the northernmost subfault, which is dipping to the east, is about 2 m, while the slips on the southern subfaults, which are steeply dipping to the west, are more than 3 m. Tsunami heights around Okushiri Island are calculated from the heterogeneous fault model using different grid sizes. Computation on the smaller grids produces large tsunami height that are closer to the observed tsunami runup heights. Tsunami propagation in the nearly closed Japan Sea is examined as the free oscillation of the Japan Sea. The excitation of the free oscillation by this earthquake is smaller than that by the 1964 Niigata or 1983 Japan Sea earthquake.     

Run-up of tsunamis and long waves in terms of surf-similarity

In this paper we review and re-examine the classical analytical solutions for run-up of periodic long waves on an infinitely long slope as well as on a finite slope attached to a flat bottom. Both cases provide simple expressions for the maximum run-up and the associated flow velocity in terms of the surf-similarity parameter and the amplitude to depth ratio determined at some offshore location. We use the analytical expressions to analyze the impact of tsunamis on beaches and relate the discussion to the recent Indian Ocean tsunami from December 26, 2004. An important conclusion is that extreme run-up combined with extreme flow velocities occurs for surf-similarity parameters of the order 3–6, and for typical tsunami wave periods this requires relatively mild beach slopes. Next, we compare the theoretical solutions to measured run-up of breaking and non-breaking irregular waves on steep impermeable slopes. For the non-breaking waves, the theoretical curves turn out to be superior to state-of-the-art empirical estimates. Finally, we compare the theoretical solutions with numerical results obtained with a high-order Boussinesq-type method, and generally obtain an excellent agreement.     

The source of the 1722 Algarve earthquake: evidence from MCS and Tsunami data

The 27 December 1722 Algarve earthquake destroyed a large area in southern Portugal generating a local tsunami that inundated the shallow areas of Tavira. It is unclear whether its source was located onshore or offshore and, in any case, what was the tectonic source responsible for the event. We analyze available historical information concerning macroseismicity and the tsunami to discuss the most probable location of the source. We also review available seismotectonic knowledge of the offshore region close to the probable epicenter, selecting a set of four candidate sources. We simulate tsunamis produced by these candidate sources assuming that the sea bottom displacement is caused by a compressive dislocation over a rectangular fault, as given by the half-space homogeneous elastic approach, and we use numerical modeling to study wave propagation and run-up. We conclude that the 27 December 1722 Tavira earthquake and tsunami was probably generated offshore, close to 37°01′N, 7°49′W.     

The relationship between political ideology and current earthquake and tsunami preparedness

Previous studies have revealed that political ideology can influence motivations for individual preparedness to mitigate the effects of climate change. Few studies have examined its role in individual preparedness behaviors to reduce the impacts of other natural hazards, such as earthquakes and tsunamis. The purpose of this study is to explore the influence of political ideology on current individual earthquake and tsunami preparedness behaviors among inhabitants of Chile's coastal areas. A statistically representative sample of the Valparaíso Region (N = 500) participated in this study. They were part of a more extensive study conducted between 2018 and 2019 in cities along the Chilean coastline, intending to study preparedness for multiple natural hazards. The survey evaluated trust in government authorities regarding emergency management, current earthquake/tsunami preparedness behaviors, and political ideology. The results reveal that political ideology is a relevant factor in predicting emergency preparedness behaviors and is significantly related to trust in government authorities. The individuals located on the right extreme of both dimensions of political ideology (those self-identified as right-wing and/or pro-market) report a higher level of current earthquake/tsunami preparedness, compared to their respective groups. Thus, for future design and implementation of natural disaster preparedness strategies and programs, the agencies in charge should recognize the role of political ideology.     

Analysis of seismological and tsunami data from the 1993 Guam earthquake

The fault parameters of the Guam earthquake of August 8, 1993 are estimated from seismological analyses, and the possibility of identifying the actual fault plane from tsunami waveforms is tested. The Centroid Moment Tensor solution of long-period surface waves shows one nodal plane shallowly dipping to the north and the other nodal plane steeply dipping to the south. The seismic moment is 3.5×10²⁰ Nm and the corresponding moment magnitude is 7.7. The Moment Tensor Rate Function inversion ofP waves also yields a similar focal mechanism and seismic moment. The point source depth is estimated as 40–50 km.This earthquake generated tsunamis that propagated toward the Japanese coast along the Izu-Bonin-Mariana ridge system. The tsunamis are recorded on ocean bottom pressure gauges and tide gauges. Numerical computation of tsunamis shows that the computed waveforms from the two possible fault planes match well with the observed tsunami waveforms. The numerical computation also shows that the tsunami waveforms at Guam Island, just above the fault, should contain useful information regarding the identification of the actual fault plane. However, the current sampling rate of the tide gauges is so small that the records cannot help the identification.     

Building a park,immunising life: Environmental management and radical asymmetry

This paper engages in a critical assessment of environmental management as a way of rethinking our co-habitation with earthly powers. Focusing on the post-disaster reconstruction of Constitución, a Chilean costal city severely damaged by the 2010 tsunami, we argue that environmental management theory has not fully recognised that, sometimes, we humans confront excessive forces that cannot be diplomatically managed or assumed as manageable objects that will readily accept our invitation to compose a common world.Thinking with Sloterdijk’s notions of atmosphere and immunisation, this paper proposes a theoretical programme to re-frame post-disaster environmental management as the creation of life-enabling membranes to contain, isolate and immunise human existence from indifferent forces such as tsunamis. More specifically, we follow the technopolitical controversies around the design of an anti-tsunami park in Constitución to draw attention towards two crucial moments of this process: the definition of the park’s composition and the debate around the park’s fallibility. We argue that these moments point to a type of environmental management engaged in the articulation of an immunising atmosphere to secure an interior for human dwelling. Moreover, these two moments specify empirical challenges not fully developed in Sloterdijk’s atmospheric philosophy: the rearrangement of science, politics and materials that is brought along in the process of erecting an immunological membrane; and the bioeconomy of life (and death) that emerges upon the possibility of an immunitary breakdown. In the concluding section we turn to the ecological and ethical challenges opened up by an atmospheric approach to environmental management.     

Assessment of tsunami hazard in the Italian seas

A method for the evaluation of tsunami potential in the seas surrounding Italy is presented. A major difficulty for performing reliable estimates of tsunami occurrence is that the existing tsunami catalog for Italy includes a small number of cases. This is due partly to the catalog incompleteness, strangely more pronounced in our century, and partly to the relative infrequency of tsunamis along the Italian seas. Evaluation of tsunami activity is therefore deduced by complementing the tsunami catalog data with data on seismicity that are by far more abundant and reliable. Analysis of seismicity and assessment of earthquake rate in coastal and submarine regions form the basis of the present method to perform tsunami potential estimates for Italy. One essential limitation of the method is that only tsunamis of seismic origin are taken into account, which leads to an underestimation of the tsunami potential. Since tsunamis generated by earthquakes are much more frequent than events produced by slumps or volcanic eruptions, the underestimation is not dramatic and very likely affects only a limited portion of the Italian coasts. In the present application of the method, eight separate regions have been considered that together cover all the coasts of Italy. In each region, seismicity has been independently examined and the earthquake potential has been calculated in small 20 × 20 cells. Then, on the basis of suitable assumptions, tsunami potential has been evaluated in each cell. According to this study, the Italian coasts that are the most exposed to the attacks of locally generated tsunamis are to be found in the Messina Straits, in Tyrrhenian coasts of Calabria, in the Ionian Sicilian coasts around Catania, and in the Gargano promontory in the Southern Adriatic Sea. Furthermore, this study confirms that the Northern Adriatic Sea has a low level of tsunami potential, in agreement with recent studies emphasizing that the large historical events concerning this region included in the first versions of the Italian tsunami catalog are largely overestimated and must be decreased.