早大学位記番号:新6661早稲田大

Aranguiz Rafael

早稲田大学博士(工学)早大学位記番号:新6661doctoral thesi

アランギス, ラファエル

27432

Aranguiz, Rafael

Waseda University Repository

Analysis of Tsunami Propagation in Coastal Areas -Lessons from Past Tsunamis-

DSpace at Waseda University

   Graduate School of Creative Science and Engineering, Waseda University     ?? ?? ?? ?? ?? ? Doctoral Thesis Synopsis     ? ? ? ? ? ? ?  Thesis Theme  Analysis of Tsunami Propagation in Coastal Areas - Lessons from Past Tsunamis -  ??????????????? - ????????????? -     ?? ? ?? ? ? (Applicant Name)  Rafael  ARÁNGUIZ  ?????  ?????       December, 2013       The Dissertation analyzes the tsunami behavior in coastal areas in Central Chile and improves the understanding of the main variables which affect tsunami propagation and runup. The reason to study this topic is due to diverse effects that the last tsunami, which occurred in February 2010, generated along the coast. As a matter of fact, field surveys showed that the southern shores of the Bay of Concepcion and Gulf of Arauco experienced large runups, while eastern shores did not. Moreover, it was observed that the 2km-wide Biobio River, located at the northeastern side the Gulf, did not experience any surge, while the seawater surged up to 2km inland in other rivers. In addition, historical records show that the Bay of Concepcion has been affected for several tsunamis the last 500 years, and large tsunamis from central and northern Chile showed similar behavior. However, the tsunami generated by the magnitude 9.5 earthquake in 1960 did not cause severe damage. In fact, the reported tsunami inundation height was half of the inundation observed during the 2010 tsunami. It is thought that the southern location of the tsunami source and the northward orientation of the Bay are the main reasons behind this. However, another smaller Bay located a few kilometers north of Bay of Concepcion, also with a northward direction, did experience a large inundation similar to that in 2010. It is not immediately obvious, looking at the existing literature, why the area around the Biobio River did not experience inundation, while in the Bay of Concepcion the wave underwent large amplification in some cases.  The present thesis consists of 5 chapters. The first one is the introduction, which gives a general overview of the study area and the tsunami research after the last events in 2004, 2010 and 2011. This chapter also provides a brief description of the significance of the present study concerning the influence of bathymetry in tsunami propagation. Then the main objectives and scope of this research are presented. The main objective of this research is the analysis of the effect of bathymetry on tsunami propagation and inundation during past events, and with this objective in mind the behaviour of the wave in the Biobio región was analyzed in detail. Then, the danger posed by future potential tsunamis was investigated, revealing the great threat that these events represent for coastal settlements in the area.  In order to explain the effects of bathymetry on tsunami propagation, a literature review is presented in Chapter 2. This chapter includes a description of tsunami generation in subduction zones, tsunamis propagation and the interaction with the coast. Literature review indicates that tsunami propagation is affected by several phenomena such as diffraction, refraction, shoaling, reflection and resonance. All these processes cause tsunamis energy to be focused or defocused. Tsunami propagation over abrupt changes in bathymetry is analyzed in detail, due to the fact that several phenomena are presented in this situation. When a tsunami wave encounters an abrupt change in bathymetry such as a step, the tsunami wave is partially reflected and partially transmitted. In addition, if the tsunami wave approaches the step at an oblique angle, it could be fully reflected or partially transmitted. Moreover, the refraction causes the wave front to turn even more normal to the step. Some basic concepts related to tsunami inundation are also defined in this chapter, such as runup, inundation height, flow depth, and inundation area. Chapter 3 is the main body of the present research. This chapter deals with the analysis of past tsunamis generated in the Chilean margin which propagated to the Biobio Region. The first section gives a general description of the event analyzed, namely the 2010 earthquake and tsunami, the magnitude-9.5 event in southern No.1      Chile in 1960 and the 1877 Iquique earthquake and tsunami in northern Chile. Numerical simulations of these three events were carried out with the NEOWAVE software, described in section 2 of that chapter. This model considers non-linear shallow water equations and non hydrostatic pressure component. To do this the tsunami’s initial conditions were selected from proposed rupture models, which involved a careful selection of a wide range of parameters such as focal depth, rising time and location, in order to obtain results that are in agreement with tsunami inundation records. In the case of the 1877 Iquique tsunami, it was also necessary to predict the tidal level in order to select an adequate rupture model, due to the fact that there were no instrumental records at that time. The finite fault models of the 2010 and 1960 events were shown to provide good results in the Biobio Region, while uniform initial condition was used in the 1877 tsunami. The numerical simulation considered 10 hours of elapsed time. The analysis considered the spectral analysis of waveforms in both deepwater, the continental shelf and inside the Bay of Concepcion. The analysis also includes the maximum inundation heights in both the Bay of Concepcion and the Gulf of Arauco in order to analyze possible effects at the Biobio River mouth. The results showed that both the 2010 and 1877 tsunamis showed well defined waves of large periods inside the Bay of Concepcion. In addition, the maximum inundation took place during the second wave in both cases. Moreover, spectral energy was amplified inside the Bay of Concepcion at a resonant periodic component between 90 and 100min. In the case of the 1960 event, there was also spectral energy amplification but it was not as significant as in the previous two scenarios. Moreover, the amplification took place at higher and lower periodic components than 95min, namely, at 30min, and 130min.  The maximum tsunami inundation heights demonstrated that the Bay of Concepción always experienced the largest inundation heights at the southern shore, similar to the Gulf of Arauco. However, the eastern shore of the Gulf showed to have low inundation height at the river mouth, which is in good agreement with field surveys carried out during the 2010 Chile tsunami. In addition, small tsunami height amplifications were observed at both sides of the river mouth. On those grounds, the seabed morphology as well as the topography was analyzed in order to find a possible explanation to such behavior. The effect of local bathymetry on tsunami propagation in the Biobio Region was thus analyzed in section 4. This section analyzed the effect of the submarine canyon located at the northern side of the Gulf of Arauco, just in front of the Biobio River. The literature review indicated that submarine canyons could amplify tsunami runup, which is the opposite of what was observed at the Biobio Region. Therefore, numerical simulations of different tsunami scenarios were carried out over an idealized bathymetry of the canyon such that the tsunami behavior was isolated from other effects. The length, width and depth of the canyon were varied, as well as the tsunami wave length. Since more than 300 simulations were performed, the TUNAMI model, which also uses shallow water equations, was used to analyze this effect. It was found that the submarine canyon has a significant influence on tsunami propagation. The most important variables are the length and width of the canyon, with the depth playing a much less important part. The canyon essentially causes a spatial variation of the wave amplitude along the coastline. While the runup in front of the canyon is always lower than in the case without the canyon, there are tsunami amplification zones at each side of the canyon. In addition, with the results of this research it is possible to explain the tsunami behavior in other submarine canyons too. Section 4 also included the resonance analysis of the Bay of Concepcion. The natural oscillation modes of the Bay were No.2      determined by means of Empirical Orthogonal Functions. This method was selected because it allows the normal modes to be obtained without a-priori restricting the resonant area. It identifies the normal modes of a data set of concatenated time-series collected from different tsunami scenarios generated inside the basin. The fundamental oscillation period was found to be 95min, which coincides with the resonant period from the spectral analysis of 2010 and 1877 event, i.e. the tsunami waves excite the fundamental period of the Bay. The second and third oscillation modes of the Bay have periods of 37 and 32 min, respectively, which are close to one of the resonant periodic components during the 1960 tsunami. Therefore, the relative low amplification given by the 1960 tsunami was due to excitation of a higher frequency oscillation rather than the fundamental period.  The effect of possible future tsunamis on the Bay of Concepcion is analyzed in Chapter 4. Since a seismic gap in northern Chile has been identified, a tsunami in that region was considered in the analysis. Hypothetical scenarios with magnitudes ranging from 8.0 to 8.8 were defined by means of empirical expressions of magnitude and size of the earthquake. The focal depth as well as the tidal level was varied for each event. A polynomial expression was fitted to the maximum tsunami wave amplitude at Talcahuano. Based on those results, the first forecast model for Talcahuano with pre-computing tsunami sources was developed. This model uses the earthquake magnitude, the focal depth and tidal level to determine maximum tsunami amplitude at Talcahuano.  Finally, Chapter 5 presents the conclusions of the present research as well as indicate areas of research that should be prioritized in the future.    No.3    No.1 ?????? ??????? ????? ????? (List of research achievements for application of doctorate (Dr. of Engineering), Waseda University)  ? ?(Full Name)? Rafael Aránguiz? ? ? ? ? ? ? (            ) ?As of October, 2013? ? ? ?(By Type) ? ? ???? ? ??????????? ? ????????? ? ??????????(theme, journal name, date & year of publication, name of authors inc. yourself) Jounals ○1)    ○2)    ○3)     ○4)    ○5)    ○6)      ○7)     ○8)    Conferences ○1)    ○2)  Tsunamis from the Arica-Tocopilla Source Region and their Effects on Ports of Central Chile  Natural Hazards, published 27 October, 2013, doi:10.1007/s11069-013-0906-5  Aránguiz, R., Shibayama, T., Yamazaki, Y.   Effect of Submarine Canyons on tsunamis propagation: Case study of Biobio Canyon  Coastal Engineering Journal, 55(4), 1350016, (2013)  Aránguiz, R., Shibayama, T.   Classiﬁcation of Tsunamis and Evacuation Areas  Natural Hazards, 67(2), 365-386, (2013)  Shibayama, T., Esteban, M., Nistor, I., Takagi, H., Thao, N. D., Matsumaru, R., Mikami, T., Aranguiz, R., Jayaratne, R., Ohira, K.   Tsunami Risk in Tubul Town: Extreme Events and Post-earthquake Territorial Transformations  Revista Geografía Norte Grande, 53, 85-106, (2012), (In Spanish with English abstract) Martínez, C., Rojas, O., Aránguiz, R., Belmonte, A., Altamirano, A. P. Flores   Use of trees as a tsunami natural barrier for Concepción, Chile  Journal of Coastal Research, SI 64, 450-454, (2011)  Aránguiz, R., Villagrán, M., Eyzaguirre, G   Field survey of tsunami disaster in Chile 2010  Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 67(2), I_529-I_534, (2011), (In Japanese with English abstract)  Mikami, T., Shibayama, T., Takewaka, S., Esteban, M., Ohira, K., Aranguiz, R., Villagran, M. & Ayala, A.   Numerical Simulation of the 2010 Chile Tsunami in the Bay of Concepcion with non-uniform initial condition  Revista Obras y Proyectos, 8, 12-18, (2010), (In Spanish)  Aránguiz, R.   Effect of tsunami breakwater as a mitigation measure at the Bay of Concepción  Revista Obras y Proyectos 8, 2-7, (2010), (In Spanish) Van Adrichem, R., Aránguiz, R.     Generation of the 1960 Tsunami in Southern Chile.  XXI Chilean Congress of Hydraulic Engineering, Oct-2013, Chile, (In Spanish) Aránguiz, R.   Beach Profile Study of a Lacustrine System using a Low-Cost Wave Recorder  Coastal Dynamics 2013, June-2013, France  Aranguiz, R. Villagrán, M.    No.2 ?????? ??????? ????? ????? (List of research achievements for application of doctorate (Dr. of Engineering), Waseda University)  ? ? ?By Type ? ? ???? ? ??????????? ? ????????? ? ??????????(theme, journal name, date & year of publication, name of authors inc. yourself) ○3)    ○4)    ○5)    ○6)     ○7)    ○8)    ○9)    ○10)     Research Projects  1)    2) Tsunami propagation from northern Chile to the Bay of San Vicente, Chile, (In Spanish) XXXII Congress of Marine Sciences, Oct-2012, Chile  Aránguiz, R.   Effect in the Bay of Concepcion of a tsunami from northern Chile  XXV Latinamerican Congress of Hydraulics, Sept-2012, Costa Rica, (In Spanish) Aránguiz, R., Belmonte, A.   The Effect of a submarine canyon on tsunami propagation in the Gulf of Arauco.  International Conference of Coastal Engineering, ICCE-2012, July-2012, Spain  Aránguiz, R.   Stability of Ruble Mound Breakwater against Solitary Waves  International Conference of Coastal Engineering, ICCE-2012, July-2012, Spain  Esteban, M., Aranguiz, R., Morikubo, I., Mikami, T., Danh Thao, N., Ohira, K., Ohtani, A., Shibayama, T.,  Preliminary study on the effect of Subamrine Canyons on tsunami propagation  XX Chilean Congress of Hydraulic Engineering, Oct-2011, Chile, (In Spanish) Aránguiz, R.   The effect of the Santa María Island on Tsunami propagation.  XX Chilean Congress of Hydraulic Engineering, Oct-2011, Chile, (In Spanish) Jimenez, M., Aránguiz, R.  Disaster Mitigation after the 2010 Chilean Earthquake and Tsunami  8th Int. Workshop on Coastal Disaster Prevention, Sept-2011, Japan  Aranguiz, R.,   Tsunami Inundation simulation in the Bay of Concepcion, Chile, using TUNAMI and Delft3D models. European Geosciences Union, Assembly 2011. April-2011, Austria. Van Adrichem, R, Aranguiz, R, Vatvani, D      Enhancement of Technology for Development of Tsunami-Resilient Community  JICA-SATREPS, period 2012-2015 Role: Leader of working group 2 in Chilean side   Research and Integrated Managament of Natural Distasters Center (CIGIDEN) (Centro de Investigación y Gestión Integrada de Desastres Naturales). FONDAP (Chilean Government) 2013-2018 Role: Researcher  

沿岸域における津波の伝播の解析 -過去の津波の事例をふまえて-

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沿岸域における津波の伝播の解析 -過去の津波の事例をふまえて-

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