Estimation of Tsunami Risk for the Coasts of Peru and Northern Chile

Data for tsunamigenic earthquakes and observed tsunami run-up are used to estimate tsunami-risk for the coasts of Peru and northern Chile for zones bounded by 5–35° S latitude. Tsunamigenic earthquake estimates yield magnitudes of 8.52, 8.64, and 8.73 for recurrence periods of 50, 100, and 200 years, respectively. Based on three different empirical relations between earthquake magnitudes and tsunamis, we estimate expected tsunami wave heights for various return periods. The average heights were 11.2 m (50 years), 13.7 m (100 years), and 15.9 m (200 years), while the maximum height values (obtained by Iidas method) were: 13.9, 17.3, and 20.4 m, respectively. Both the averaged and maximum seismological estimates of tsunami wave heights for this region are significantly smaller than the actually observed tsunami run-up of 24–28 m, for the major events of 1586, 1724, 1746, 1835, and 1877. Based directly on tsunami run-up data, we estimate tsunami wave heights of 13 m for a 50-year return period and 25 m for a 100-year return period. According to the seismic gap theory, we can expect that the next strong earthquake and tsunami will occur between 19 and 28° S in the vicinity of northern Chile.     

Integration of the THRUST project into the Chile Tsunami Warning System

Several seismic gaps are identified along the coast of Chile. The main one is located in the northern part of the country (18° S–20° S), where a THRUST seismic trigger has been installed; two more triggers will be placed in other seismic gaps. The Standard Operations Plan (SOP) was tested during a disaster simulation exercise based on a major earthquake and tsunami situation. Response actions by governmental and civil agencies were monitored and a performance evaluation was done. Modifications of the SOP were found necessary to adjust the interactions between agencies.     

Probabilistic Analysis of Tsunami Hazards*

Determining the likelihood of a disaster is a key component of any comprehensive hazard assessment. This is particularly true for tsunamis, even though most tsunami hazard assessments have in the past relied on scenario or deterministic type models. We discuss probabilistic tsunami hazard analysis (PTHA) from the standpoint of integrating computational methods with empirical analysis of past tsunami runup. PTHA is derived from probabilistic seismic hazard analysis (PSHA), with the main difference being that PTHA must account for far-field sources. The computational methods rely on numerical tsunami propagation models rather than empirical attenuation relationships as in PSHA in determining ground motions. Because a number of source parameters affect local tsunami runup height, PTHA can become complex and computationally intensive. Empirical analysis can function in one of two ways, depending on the length and completeness of the tsunami catalog. For site-specific studies where there is sufficient tsunami runup data available, hazard curves can primarily be derived from empirical analysis, with computational methods used to highlight deficiencies in the tsunami catalog. For region-wide analyses and sites where there are little to no tsunami data, a computationally based method such as Monte Carlo simulation is the primary method to establish tsunami hazards. Two case studies that describe how computational and empirical methods can be integrated are presented for Acapulco, Mexico (site-specific) and the U.S. Pacific Northwest coastline (region-wide analysis). * The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

The Local Tsunami Alert System [``SLAT']: A Computational Tool for the Integral Management of a Tsunami Emergency

During a tsunami emergency numerous local authorities responsible for the security oflocal persons and businesses which function in the coastal zone are required to makecritical decisions within a very short time frame. It is known that the consequencesof the situation will depend on the quality and quantity of decisions which they makeor allow to occur at the critical time. Based on this concept, the Local System of Tsunami Alert (SLAT; Spanish) was developed. This is a computational tool designed for the automatic implementation of integral management for an emergency of this type.The System is able to immediately evaluate possible risks and determine thetype of alert represented (Red, Yellow, Green, Blue, and Celeste) if relevantdata such as coordinates of the epicenter, magnitude, date, and origin of theearthquake (>6.5° on the Richter scale) threatening the Pacific areknown. Other relevant data include location of the coastal or marine epicentreand the superficial hypocenter. The relevant data may now be obtained fromthe internet from international seismological services, and fed into the programto give the most probable time for arrival of the first wave train at a given pointof interest, whether this be a port, bathing area, generating plant, or coastal city.The program also gives the time required for the first wave train to arrive at agiven coast, and displays a menu of previously planned actions to be taken accordingto the type of alert. It also permits dissemination of a bulletin with critical data and action plans by fax or e-mail to scattered users as well as for storage on the computer disc. The system is designed in a way that the user always confirms with authorities that anevent has in fact been generated. On a local scale, the user is required to prepare an operative emergency plan of action to be followed by his company, community, or municipality, to be followed for each type of alert.The System permits carrying out test exercises with the users, as well as simulationof past events. Knowledge concerning past events permits understanding correctdesign of emergency action plans for mitigation of potential present and future events.This software is specifically designed for the Pacific Coast of South America, and isprepared in Spanish, with the intention of improving responses of inhabitants of coastalareas to the potential threat from tsunamis.     

The Seismic Project of the National Tsunami Hazard Mitigation Program

In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years.     

Tsunami Hazard in the Eastern Mediterranean: Strong Earthquakes and Tsunamis in the Corinth Gulf,Central Greece

The exhaustive review of a long number of historical documents, books, reports,scientific and press reports, instrumental recordings, previous catalogues andpersonal field observations, concluded with the production of a completely newtsunami catalogue for the Corinth Gulf, Central Greece, which is arranged in theformat adopted by the GITEC group for the new European Tsunami Catalogue.The catalogue is presented in three sections: the Quick-Look Table, the Quick-LookAccounts File and the References File. An Appendix explains why some particularsea disturbances were not included in the new catalogue although they were consideredas tsunami events by previous researchers. Past history clearly shows that most tsunamis in the Corinth Gulf are produced by strong (Ms 5.5) offshore and near shore earthquakes. However, seismic or aseismic sliding of coastal and submarine sediments is a significant factor in tsunamigenesis. Calculations based on the random model indicate that the probability for at least one tsunami occurrence of intensity TI 2 TI 3 and TI 4 within 50 years equals 0.851, 0.747 and 0.606, respectively. From the intensity–frequency relationship the mean return period of tsunami intensity TI 2, TI 3 and TI 4 equals to 16, 40 and 103 years. The tsunami geographicaldistribution, however, is non-random with a clear trend for the tsunamigenesis todecrease drastically from west to east within the Corinth Gulf. In fact, the probabilityfor a strong earthquake to cause a tsunami of TI 3 in the Corinth Gulf consideredas an entity is 0.35, while in the western part of the Gulf it goes up to 0.55. Therefore, the rapid and accurate determination of the earthquake focal parameters is of great importance in an algorithm of a real-time tsunami warning system in the Corinth Gulf.     

Validating a Tsunami Vulnerability Assessment Model (the PTVA Model) Using Field Data from the 2004 Indian Ocean Tsunami

The “PTVAM” tsunami vulnerability assessment model [Papathoma and Dominey-Howes: 2003, Nat. Hazards Earth Syst. Sci. 3, 733–744; Papathoma et al.: 2003, Nat. Hazards Earth Syst. Sci. 3, 377–389], like all models, requires validation. We use the results from post-tsunami surveys in the Maldives following the December 26, 2004 Indian Ocean tsunami to ‘evaluate’ the appropriateness of the PTVAM attributes to understanding spatial and temporal vulnerability to tsunami damage and loss. We find that some of the PTVAM attributes are significantly important and others moderately important to understanding and assessing vulnerability. Some attributes require further investigation. Based upon the ground-truth data, we make several modifications to the model framework and propose a revised version of the PTVAM (PTVAM 2).     

The December 26th 2004 Tsunami Recorded along the Southeastern Coast of Brazil

Sea level measurements along the southeastern Brazilian coast, between 20° S and 30° S, show the effect of the Sumatra Tsunami of December 26, 2004. Two records from stations, one located inside an estuary and other inside a bay, shows oscillations of about 0.20 m range; one additional record from a station facing the open sea shows up to 1.2 m range oscillations. These oscillations have around 45 min period, starting 20–22 h after the Sumatra earthquake in the Indian Ocean (00:59 UTC) and lasting for 2 days. A computer modelling of the event reproduces the time of arrival of long shallow-water tsunami waves at the southeastern Brazilian coast but with slight longer period and amplitudes smaller than observed at the coast, probably due to its coarse resolution (1/4 of a degree). The high amplitudes observed at the coast suggest a mechanism of amplification of these waves over the southeastern Brazilian shelf.     

Impact of the National Tsunami Hazard Mitigation Program on Operations of the Richard H. Hagemeyer Pacific Tsunami Warning Center

The first 7 years of the National Tsunami Hazard Mitigation Program (NTHMP) have had a significant positive impact on operations of the Richard H. Hagemeyer Pacific Tsunami Warning Center (PTWC). As a result of its seismic project, the amount and quality of real-time seismic data flowing into PTWC has increased dramatically, enabling more rapid, accurate, and detailed analyses of seismic events with tsunamigenic potential. Its tsunameter project is now providing real-time tsunameter data from seven strategic locations in the deep ocean to more accurately measure tsunami waves as they propagate from likely source regions toward shorelines at risk. These data have already been used operationally to help evaluate potential tsunami threats. A new type of tsunami run-up gauge has been deployed in Hawaii to more rapidly assess local tsunamis. Lastly, numerical modeling of tsunamis done with support from the NTHMP is beginning to provide tools for real-time tsunami forecasting that should reduce the incidence of unnecessary warnings and provide more accurate forecasts for destructive tsunamis.     

Longwave Measurements for the Coast of British Columbia and Improvements to the Tsunami Warning Capability

A few years ago the Canadian Hydrographic Service initiated a major upgrade toall tide gauges and tsunami stations on the coast of British Columbia (B.C.). Thisprogram was undertaken to address shortcomings of the earlier digital systems andwas driven by concerns about emergency response continuity in the year 2000. By1999, thirteen tide gauge stations had been installed and were operational. Three ofthese stations (Tofino, Winter Harbour, and Langara) were selected for use as tsunamiwarning stations. Several years of continuous, high quality data have now been collectedat these stations and used for analysis of long waves in the tsunami frequency band.Careful examination of these data revealed two weak tsunamis recorded by severalB.C. stations: a distant tsunami of June 23, 2001 generated by the Peru Earthquake(M_w = 8.4), and a local tsunami of October 12, 2001 induced by the Queen Charlotte Earthquake (M_w = 6.3$). Spectral characteristics of these two tsunamis are compared with the spectral characteristics of long waves generated by a strong storm (October, 2000) and of ordinary background oscillations. The topographic admittance functions (frequency responses) constructed for all stations showed that most of them (in particular, Winter Harbour, Tofino, Bamfield, Port Hardy, and Victoria) have strong resonance at periods from 2.5 to 20 min, indicating that these locations are vulnerable to relatively high-frequency tsunamis. The Winter Harbour station also has two strong resonant peaks with periods of 30 and 47 min and with amplification factors of about 7. The estimated source functions show very clear differences between long waves associated with the seismic source (typical periods 10–30 min) and those generated by a storm, which typically have shorter periods and strong energy pumping from high-frequencies due to non-linear interaction of wind waves.     

Potential Tsunami Hazard Associated with the Kerepehi Fault,Firth of Thames,New Zealand

Geophysical data have identified four submarine segments of the Kerepehi Fault, roughly bisecting a back-arc rift (Hauraki Rift). These segments have been traced through the shallow waters of the Firth of Thames, which lies at the southern end of the Hauraki Gulf, New Zealand. No historical or paleotsunami data are available to assess the tsunami hazard of these fault segments.Analysis of the fault geometry, combined with paleoseismic data for three further terrestrial segments of the Fault, suggest Most Credible Earthquake (MCE) moment magnitudes of 6.5–7.1. Due to the presence of thick deposits of soft sediment, and thesemi-confined nature of the Firth, the MCE events are considered capable of generating tsunami or tsunami-like waves. Two numerical models (finite element and finite difference), and an empirical method proposed by Abe (1995), were used to predict maximum tsunami wave heights. The numerical models also modelled the tsunami propagation.The MCE events were found not to represent a major threat to the large metropolitan centre of Auckland City (New Zealand's largest population centre). However, the waves were a threat to small coastal communities around the Firth, including the township of Thames, and 35,000 ha of low-lying land along the southern shores of the Firth of Thames.The Abe method was found to provide a quick and useful method of assessing the regional tsunami height. However, for sources in water depths < 25 m the Abe method predicted heights 2–4 times larger than the numerical models. Since the numerical models were not intended for simulating tsunami generation in such shallow water, the Abe results are probably a good guide to the maximum wave heights.     

Run-up and Inundation Pattern Developed During the Indian Ocean Tsunami of December 26, 2004 Along the Coast of Tamilnadu (India)

The tsunami run-up, inundation and damage pattern observed along the coast of Tamilnadu (India) during the deadliest Indian Ocean tsunami of December 26, 2004 is documented in this paper. The tsunami caused severe damage and claimed many victims in the coastal areas of eleven countries, bordering the Indian Ocean. Along the coast of Indian mainland, the damage was caused by the tsunami only. Largest tsunami run-up and inundation was observed along the coast of Nagapattinam district and was about 10–12 m and 3.0 km, respectively. The measured inundation data were strongly scattered in direct relationship to the morphology of the seashore and the tsunami run-up. Lowest tsunami run-up and inundation was measured along the coast of Thanjavur, Puddukkotai and Ramnathpuram districts of Tamilnadu in the Palk Strait. The presence of shadow of Sri Lanka, the interferences of direct/receded waves with the reflected waves from Sri Lanka and Maldive Islands and variation in the width of continental shelf were the main cause of large variation in tsunami run-up along the coast of Tamilnadu.     

Geological and Historical Investigation of the 1650 Mt. Columbo (Thera Island) Eruption and Tsunami, Aegean Sea, Greece

This paper reviews geological andhistorical evidence for the eruption and tsunamireported to have occurred in 1650 in the areaof Mt. Columbo, Thera Island, Greece. The tsunami isbelieved to have been generated as a consequence ofthe eruption of Mt. Columbo 6.5 km NE of Thera Island.Historical documents state that the tsunami flooded upto 2 miles inland and destroyed many engineeredstructures. We present lithostratigraphic evidencefrom one abandoned trench and two trench excavationsclose to sea level in the villages of Kamari andPerissa respectively, which lie well within thereported inundation zone of the tsunami. The resultspresented show that no marine- (tsunami) depositedsediments are preserved at these locations.Alternative hypotheses of discontinuous sedimentdeposition and over estimation of the event magnitudeare considered to explain the observations presentedhere. The data may have important implications for thedevelopment of hazard zone maps, risk assessment,vulnerability reduction and for emergency managementofficials.     

Preliminary estimation of the tsunami hazards associated with the Makran subduction zone at the northwestern Indian Ocean

We present a preliminary estimation of tsunami hazard associated with the Makran subduction zone (MSZ) at the northwestern Indian Ocean. Makran is one of the two main tsunamigenic zones in the Indian Ocean, which has produced some tsunamis in the past. Northwestern Indian Ocean remains one of the least studied regions in the world in terms of tsunami hazard assessment. Hence, a scenario-based method is employed to provide an estimation of tsunami hazard in this region for the first time. The numerical modeling of tsunami is verified using historical observations of the 1945 Makran tsunami. Then, a number of tsunamis each resulting from a 1945-type earthquake (M _w 8.1) and spaced evenly along the MSZ are simulated. The results indicate that by moving a 1945-type earthquake along the MSZ, the southern coasts of Iran and Pakistan will experience the largest waves with heights of between 5 and 7 m, depending on the location of the source. The tsunami will reach a height of about 5 m and 2 m in northern coast of Oman and eastern coast of the United Arab Emirates, respectively.     

A New Probabilistic Seismic Hazard Analysis for the Vrancea (Romania) Seismogenic Zone

In this paper we apply a probabilistic methodology to map specific seismic hazard induced by the Vrancea Seismogenic Zone, which represents the uttermost earthquake danger to Romania as well as its surroundings. The procedure is especially suitable for the estimation of seismic hazard at an individual site, and seismic hazard maps can be created by applying it repeatedly to grid points covering larger areas. It allows the use of earthquake catalogues with incompletely reported historical and complete instrumental parts. When applying themethodology, special attention was given to the effect of hypocentral depth and the variation of attenuation according to azimuth. Hazard maps specifying a 10% chance of exceedance of the given peak ground acceleration value for an exposure time of 50 years were prepared for three different characteristic depths of earthquakes in the Vrancea area. These maps represent a new realistic contribution to the mitigation of the earthquake risk caused by the Vrancea Seismogenic Zone in terms of: (1) input data (consistent, reliable, and the most complete earthquake catalogue), (2) appropriate and specific attenuation relationships (considering both azimuthal and depth effects); and (3) a new and versatile methodology.     

Regional Considerations of Coastline Change,Tsunami Damage and Recovery along the Southern Coast of the Bay of Izmit (The Kocaeli (Turkey) Earthquake of 17 August 1999)

Co-seismic phenomena along the south coastline included liquefaction, subsidenceand tsunami. Construction on areas composed of fluvial and alluvial sediments aswell as unconsolidated fill increased the risk by creating potential for amplificationof seismic waves. Cyclic mobility liquefaction was common along the coastline, andlevel-ground liquefaction was observed. Flow liquefaction is held forth as a possibilityin the Deirmendere submarine landslide. Damage to structures was markedly more in areas of unconsolidated sediments. One or more tsunami struck immediately after the event; the uniformity of tsunami impact indicating a wave coming from 310° suggests that submarine faulting was the major source of tsunami. Over 800,000 m² of subsidence resulted from sediment slumping, fault controlled subsidence, and possibly post-liquefaction sediment compaction. After a brief period of post-event abandonment, reclamation and use of coastal areas is well underway. This creates a tension between human desires pushing for quick and inexpensive re-inhabitation of the coastal areas, and the needs for zoning and building codes for risk reduction. In this high-risk area suchcontrary cultural mandates cannot yield ideal results. It is suggested that an alternativemodel of immediate post-event creation of parks and natural areas that would yield benefit is preferable in coastal areas rather than the enforcement approach currently favored.     

Probabilistic seismic and tsunami hazard analysis for design criteria development of a coastal area in the city of Banda Aceh

Both seismic and tsunami hazards design criteria are essential input to the rehabilitation and long-term development of city of Banda Aceh Post Sumatra 2004 (M _w=9.3) disaster. A case study to develop design criteria for future disaster mitigation of the area is presented. The pilot study consists of probabilistic seismic and tsunami hazard analysis. Results of the probabilistic seismic hazard analysis indicates that peak ground acceleration at baserock for 10 and 2% probability of exceedance in 50 years is 0.3 and 0.55 g, respectively. The analysis also provides spectral values at short (T=0.2 s) and long period (T=1.0 s) motions. Some non-linear time-domain earthquake response analyses for soft, medium, and hard site-class were conducted to recommend design response spectra for each site-class. In addition, tsunami inundation maps generated from probabilistic tsunami hazard analysis were developed through tsunami wave propagation analysis and run-up numerical modeling associated with its probability of tsunamigenic earthquake source potential. Both the seismic and tsunami hazard curve and design criteria are recommended as contribution of this study for design criteria, as part of the disaster mitigation effort in the development process of the city. The methodology developed herein could be applied to other seismic and tsunami disaster potential areas.     

基于小流域的地震扰动区降雨型滑坡泥石流危险性评价方法

地震扰动区存在大量震裂松散坡体,在持续或者密集的降雨条件下极易转化为滑坡灾害。同时,滑坡又会给泥石流提供大量松散固体物质,增加泥石流的危险性。因此,在震区,灾害通常以"链"的形式出现,比单一灾种危害性大。为了更有效地对地质灾害危险性进行评价,笔者将滑坡、泥石流作为灾害链,综合地加以分析和研究。选择5·12汶川大地震中受灾严重的都江堰市白沙河流域的17条泥石流沟作为研究区,建立滑坡-泥石流危险性评价耦合模型,研究24 h不同降雨量条件下小流域滑坡泥石流危险性的变化。耦合模型包括了坡体稳定性评价模型,水文模型及以泥石流规模、发生频率、流域面积、主沟长度、流域高差、切割密度、不稳定斜坡比为评价因子的泥石流危险性评价统计模型。研究结果表明:随着降雨量的增大,参与泥石流活动的松散物质方量持续增加,但当24 h降雨量超过200 mm后,泥石流沟的危险度等级不再发生变化;17条泥石流沟中4条为中危险度,12条为高危险度,1条为极高危险度。这说明研究区地质灾害问题相当严峻,在多雨季节存在泥石流群发的可能性,直接威胁到居住在泥石流沟附近的人民群众生命财产安全;因此,对于有直接危害对象的高危险度及其以上的泥石流沟,应该按照高等级设防标准进行工程治理及发布预警报。同时也说明,将滑坡、泥石流作为灾害链研究具必要性和可行性。