Pure and Applied Geophysics

Rabinovich, Alexander; Geist, Eric; Fritz, Hermann; Borrero, Jose

doi: 10.1007/s00024-015-1175-xpmid: N/A

Twenty papers on the study of tsunamis and respective tsunamigenic earthquakes are included in Volume II of the PAGEOPH topical issue “Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami”. The papers presented in this second of two special volumes of Pure and Applied Geophysics reflect the state of tsunami science during this time, including five papers devoted to new findings specifically in the Indian Ocean. Two papers compile results from global observations and eight papers cover Pacific Ocean studies, focusing mainly on the 2011 Tohoku earthquake and tsunami. Remaining papers in this volume describe studies in the Atlantic Ocean and Mediterranean Sea and tsunami source studies. Overall, the volume not only addresses the pivotal 2004 Indian Ocean and 2011 Tohoku tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world.

Gusiakov, Viacheslav

doi: 10.1007/s00024-015-1101-2pmid: N/A

Tsunami intensity on the Soloviev–Imamura scale is one of the most important parameters for characterizing the overall size of a tsunami generated by submarine earthquakes. Consequently, this parameter is included in both global tsunami databases maintained by the National Centers for Environmental Information/World Data Service (NCEI/WDS) and the Novosibirsk Tsunami Laboratory of the Institute of Computational Mathematics and Mathematical Geophysics (NTL/ICMMG). S. Soloviev made the initial evaluation of the intensities of a large number of destructive historical tsunamis while compiling his two historical catalogs of tsunamis in the Pacific. The Novosibirsk Tsunami Laboratory under the Expert Tsunami Database Project made further determinations of tsunami intensity for the events after 1975. These intensities have been periodically incorporated into the NCEI/WDS tsunami database under the Global Tsunami Database Joint ICG/ITSU-IUGG/TC Project. In the on-line version of the NCEI/WDS Tsunami Database, the data on tsunami intensity are available only for the events prior to 2003. The main purpose of this paper is to extend the temporal coverage of this important parameter for characterizing tsunamigenic events to the present in order to provide researchers with more data for analyzing the temporal and spatial tsunami occurrence. However, of the 164 tsunamigenic events in the World Ocean from 2000 to the present, we could determine the intensity value for only 44 events that is less than 27 % of the total. For the rest of the events (that is, 73 %), the intensity value cannot be determined due to the lack of data on wave heights from the nearest coast. This shows that despite a great improvement in the tsunami-recording network in the Pacific and other oceanic basins during the last two decades, the data for reliable estimates of tsunami intensity are still problematic.

Rabinovich, Alexander; Eblé, Marie

doi: 10.1007/s00024-015-1058-1pmid: N/A

Deep-ocean tsunami measurements play a major role in understanding the physics of tsunami wave generation and propagation, and in improving the effectiveness of tsunami warning systems. This paper provides an overview of the history of tsunami recording in the open ocean from the earliest days, approximately 50 years ago, to the present day. Modern tsunami monitoring systems such as the self-contained Deep-ocean Assessment and Reporting of Tsunamis and innovative cabled sensing networks, including, but not limited to, the Japanese bottom cable projects and the NEPTUNE-Canada geophysical bottom observatory, are highlighted. The specific peculiarities of seafloor longwave observations in the deep ocean are discussed and compared with observations recorded in coastal regions. Tsunami detection in bottom pressure observations is exemplified through analysis of distant (22,000 km from the source) records of the 2004 Sumatra tsunami in the northeastern Pacific.

Suppasri, Anawat; Goto, Kazuhisa; Muhari, Abdul; Ranasinghe, Prasanthi; Riyaz, Mahmood; Affan, Muzailin; Mas, Erick; Yasuda, Mari; Imamura, Fumihiko

doi: 10.1007/s00024-015-1134-6pmid: N/A

The 2004 Indian Ocean tsunami was one of the most devastating tsunamis in world history. The tsunami caused damage to most of the Asian and other countries bordering the Indian Ocean. After a decade, reconstruction has been completed with different levels of tsunami countermeasures in most areas; however, some land use planning using probabilistic tsunami hazard maps and vulnerabilities should be addressed to prepare for future tsunamis. Examples of early-stage reconstruction are herein provided alongside a summary of some of the major tsunamis that have occurred since 2004, revealing the tsunami countermeasures established during the reconstruction period. Our primary objective is to report on and discuss the vulnerabilities found during our field visits to the tsunami-affected countries—namely, Indonesia, Sri Lanka, Thailand and the Maldives. For each country, future challenges based on current tsunami countermeasures, such as land use planning, warning systems, evacuation facilities, disaster education and disaster monuments are explained. The problem of traffic jams during tsunami evacuations, especially in well-known tourist areas, was found to be the most common problem faced by all of the countries. The readiness of tsunami warning systems differed across the countries studied. These systems are generally sufficient on a national level, but local hazards require greater study. Disaster reduction education that would help to maintain high tsunami awareness is well established in most countries. Some geological evidence is well preserved even after a decade. Conversely, the maintenance of monuments to the 2004 tsunami appears to be a serious problem. Finally, the reconstruction progress was evaluated based on the experiences of disaster reconstruction in Japan. All vulnerabilities discussed here should be addressed to create long-term, disaster-resilient communities.

Okal, Emile; Fritz, Hermann; Hamzeh, Mohammad; Ghasemzadeh, Javad

doi: 10.1007/s00024-015-1157-zpmid: N/A

We report the result of a 2010 survey of the effects on the Iranian coastline of the tsunami which followed the earthquake of 27 November 1945 (M 0 = 2.8 × 1028 dyn cm; M w = 8.2), the only large event recorded along the Makran subduction zone since the onset of instrumental seismology. Based on the interview of elderly survivors of the event, we obtained a database of nine values of run-up or splash amplitudes on a segment of shore extending 280 km from Souraf in the West to Pasabandar near the Pakistani border, and ranging in vertical amplitude from 2.3 to 13.7 m. Witness reports are consistent with a significant delay (estimated at ~2.5 h) of the tsunami waves, suggesting that they were generated by an ancillary phenomenon, such as a landslide triggered by the earthquake. None of our witnesses bore ancestral memory of comparable events in the past, suggesting that reported predecessors to the 1945 earthquake may have been smaller in size. The survey also allowed the compilation of previously unreported data concerning the effects of the 2004 Sumatra–Andaman tsunami.

Premasiri, Ranjith; Styles, Peter; Shrira, Victor; Cassidy, Nigel; Schwenninger, Jean-Luc

doi: 10.1007/s00024-015-1128-4pmid: N/A

To evaluate and mitigate tsunami hazard, as long as possible records of inundations and dates of past events are needed. Coastal sediments deposited by tsunamis (tsunamites) can potentially provide this information. However, of the three key elements needed for reconstruction of palaeotsunamis (identification of sediments, dating and finding the inundation distance) the latter remains the most difficult. The existing methods for estimating the extent of a palaeotsunami inundation rely on extensive excavation, which is not always possible. Here, by analysing tsunamites from Sri Lanka identified using sedimentological and paleontological characteristics, we show that their internal dielectric properties differ significantly from surrounding sediments. The significant difference in the value of dielectric constant of the otherwise almost indistinguishable sediments is due to higher water content of tsunamites. The contrasts were found to be sharp and not to erode over thousands of years; they cause sizeable electromagnetic wave reflections from tsunamite sediments, which permit the use of ground-penetrating radar (GPR) to trace their extent and morphology. In this study of the 2004 Boxing Day Indian Ocean tsunami, we use GPR in two locations in Sri Lanka to trace four identified major palaeotsunami deposits for at least 400 m inland (investigation inland was constrained by inaccessible security zones). The subsurface extent of tsunamites (not available without extensive excavation) provides a good proxy for inundation. The deposits were dated using the established method of optically stimulated luminescence (OSL). This dating, partly corroborated by available historical records and independent studies, contributes to the global picture of tsunami hazard in the Indian Ocean. The proposed method of combined GPR/OSL-based reconstruction of palaeotsunami deposits enables estimates of inundation, recurrence and, therefore, tsunami hazard for any sandy coast with identifiable tsunamite deposits. The method could be also used for anchoring and synchronizing chronologies of ancient civilisations adjacent to the ocean shores.

Hébert, H.; Schindelé, F.

doi: 10.1007/s00024-015-1136-4pmid: N/A

The 2004 Indian Ocean tsunami gave the opportunity to gather unprecedented tsunami observation databases for various coastlines. We present here an analysis of such databases gathered for 3 coastlines, among the most impacted in 2004 in the intermediate- and far field: Thailand–Myanmar, SE India–Sri Lanka, and SE Madagascar. Non-linear shallow water tsunami modeling performed on a single 4′ coarse bathymetric grid is compared to these observations, in order to check to which extent a simple approach based on the usual energy conservation laws (either Green’s or Synolakis laws) can explain the data. The idea is to fit tsunami data with numerical modeling carried out without any refined coastal bathymetry/topography. To this end several parameters are discussed, namely the bathymetric depth to which model results must be extrapolated (using the Green’s law), or the mean bathymetric slope to consider near the studied coast (when using the Synolakis law). Using extrapolation depths from 1 to 10 m generally allows a good fit; however, a 0.1 m is required for some others, especially in the far field (Madagascar) possibly due to enhanced numerical dispersion. Such a method also allows describing the tsunami impact variability along a given coastline. Then, using a series of scenarios, we propose a preliminary statistical assessment of tsunami impact for a given earthquake magnitude along the Indonesian subduction. Conversely, the sources mostly contributing to a specific hazard can also be mapped onto the sources, providing a first order definition of which sources are threatening the 3 studied coastlines.

Mas, Erick; Koshimura, Shunichi; Imamura, Fumihiko; Suppasri, Anawat; Muhari, Abdul; Adriano, Bruno

doi: 10.1007/s00024-015-1105-ypmid: N/A

As confirmed by the extreme tsunami events over the last decade (the 2004 Indian Ocean, 2010 Chile and 2011 Japan tsunami events), mitigation measures and effective evacuation planning are needed to reduce disaster risks. Modeling tsunami evacuations is an alternative means to analyze evacuation plans and possible scenarios of evacuees’ behaviors. In this paper, practical applications of an agent-based tsunami evacuation model are presented to demonstrate the contributions that agent-based modeling has added to tsunami evacuation simulations and tsunami mitigation efforts. A brief review of previous agent-based evacuation models in the literature is given to highlight recent progress in agent-based methods. Finally, challenges are noted for bridging gaps between geoscience and social science within the agent-based approach for modeling tsunami evacuations.

Lui, Semechah; Helmberger, Don; Wei, Shengji; Huang, Yihe; Graves, Robert

doi: 10.1007/s00024-015-1042-9pmid: N/A

Results from the 2011 Mw 9.1 Tohoku-Oki megathrust earthquake display a complex rupture pattern, with most of the high-frequency energy radiated from the downdip edge of the seismogenic zone and very little from the large shallow rupture. Current seismic results of smaller earthquakes in this region are confusing due to disagreements among event catalogs on both the event locations (>30 km horizontally) and mechanisms. Here we present an in-depth study of a series of intraslab earthquakes that occurred in a localized region near the downdip edge of the main shock. We explore the validity of 1D velocity model and refine earthquake source parameters for selected key events by performing broadband waveform modeling combining regional networks. These refined source parameters are then used to calibrate paths and further simulate secondary source properties, such as rupture directivity and fault dimension. Calculation of stress changes caused by the main event indicate that the region where these intraslab events occurred are prone to thrust events. This group of intraslab earthquakes suggest the reactivation of a subducted normal fault, and are potentially useful in enhancing our understanding on the downdip shear zone and large outer-rise events.

Baba, Toshitaka; Takahashi, Narumi; Kaneda, Yoshiyuki; Ando, Kazuto; Matsuoka, Daisuke; Kato, Toshihiro

doi: 10.1007/s00024-015-1049-2pmid: N/A

Because of improvements in offshore tsunami observation technology, dispersion phenomena during tsunami propagation have often been observed in recent tsunamis, for example the 2004 Indian Ocean and 2011 Tohoku tsunamis. The dispersive propagation of tsunamis can be simulated by use of the Boussinesq model, but the model demands many computational resources. However, rapid progress has been made in parallel computing technology. In this study, we investigated a parallelized approach for dispersive tsunami wave modeling. Our new parallel software solves the nonlinear Boussinesq dispersive equations in spherical coordinates. A variable nested algorithm was used to increase spatial resolution in the target region. The software can also be used to predict tsunami inundation on land. We used the dispersive tsunami model to simulate the 2011 Tohoku earthquake on the Supercomputer K. Good agreement was apparent between the dispersive wave model results and the tsunami waveforms observed offshore. The finest bathymetric grid interval was 2/9 arcsec (approx. 5 m) along longitude and latitude lines. Use of this grid simulated tsunami soliton fission near the Sendai coast. Incorporating the three-dimensional shape of buildings and structures led to improved modeling of tsunami inundation.