Numerical Study of Tsunami Generated by Multiple Submarine Slope Failures in Resurrection Bay, Alaska, during the M W 9.2 1964 Earthquake

We use a viscous slide model of Jiang and LeBlond (1994) coupled with nonlinear shallow water equations to study tsunami waves in Resurrection Bay, in south-central Alaska. The town of Seward, located at the head of Resurrection Bay, was hit hard by both tectonic and local landslide-generated tsunami waves during the M _W 9.2 1964 earthquake with an epicenter located about 150 km northeast of Seward. Recent studies have estimated the total volume of underwater slide material that moved in Resurrection Bay during the earthquake to be about 211 million m³. Resurrection Bay is a glacial fjord with large tidal ranges and sediments accumulating on steep underwater slopes at a high rate. Also, it is located in a seismically active region above the Aleutian megathrust. All these factors make the town vulnerable to locally generated waves produced by underwater slope failures. Therefore it is crucial to assess the tsunami hazard related to local landslide-generated tsunamis in Resurrection Bay in order to conduct comprehensive tsunami inundation mapping at Seward. We use numerical modeling to recreate the landslides and tsunami waves of the 1964 earthquake to test the hypothesis that the local tsunami in Resurrection Bay has been produced by a number of different slope failures. We find that numerical results are in good agreement with the observational data, and the model could be employed to evaluate landslide tsunami hazard in Alaska fjords for the purposes of tsunami hazard mitigation.     

Note on the 1964 Alaska Tsunami Generation by Horizontal Displacements of Ocean Bottom. Numerical Modeling of the Runup in Chenega Cove, Alaska

A numerical model of the wave dynamics in Chenega Cove, Alaska during the historic M _w 9.2 megathrust earthquake is presented. During the earthquake, locally generated waves of unknown origin were identified at the village of Chenega, located in the western part of Prince William Sound. The waves appeared shortly after the shaking began and swept away most of the buildings while the shaking continued. We model the tectonic tsunami in Chenega Cove assuming different tsunami generation processes. Modeled results are compared with eyewitness reports and an observed runup. Results of the numerical experiments let us claim the importance of including both vertical and horizontal displacement into the 1964 tsunami generation process. We also present an explanation for the fact that arrivals of later waves in Chenega were unnoticed.     

Relation between the Subducting Plate and Seismicity Associated with the Great 1964 Alaska Earthquake

—Tectonic studies of the great 1964 Alaska earthquake have underappreciated the nature of the subducted plate in influencing seismicity. We compare seismological observations in the Prince William and Kodiak areas that ruptured during this earthquake with the corresponding morphology and structure of the subducting plate. The upper plate geology (Prince William Terrane) and velocity structure are the same in both areas. In the Prince William area where the Yakutat Terrane subducted, the energy released and coupling were stronger than above the Kodiak subduction zone where thick trench sediment subducts. The conjecture that lower plate character or the amount of subducted sediment affects coupling helps explain variability in seismology, geodetic inversions and the horizontal velocity of GPS stations.     

关于印度洋地震海啸紧急救援的两个问题

海退是海浪剧变的重要信号,发生海退现象之后,应当立即撤离沿海,跑到高地上去,才能避免人员的重大伤亡。红树林在印度洋地震海啸中起到减缓作用。红树林生态系统是生产率最高的海洋四大自然生态系统之一,是国际上生物多样性保护和湿地保护对象,被誉为“地球的肾”。在全球红树林锐减的情况下,广西防城港红树林项目的启动是被全球环境基金会称为典范。     

Tsunami Wave Analysis and Possibility of Splay Fault Rupture During the 2004 Indian Ocean Earthquake

The 2004 Indian Ocean tsunami was observed by two satellites, close in space and time, that traversed the Indian Ocean 2?h after the Sumatra–Andaman earthquake, but which observed different tsunami lead wave morphologies. The earlier satellite, Jason-1, recorded a lead wave with two peaks of similar amplitude and wavelength, while the later satellite, TOPEX/Poseidon, recorded a lead wave with only one longer wavelength uplift. To resolve this disparity, we examine the travel paths of long wavelength waves over the seafloor bathymetry. Waves traveling from the margin will traverse significantly different paths to arrive at the two satellite transects. The result is that the satellites are sensitive to different parts of the margin; Jason-1 is highly sensitive to the margin in the area of the epicenter, while TOPEX is sensitive to a more northerly section. By developing solutions of the ocean gravity wave equations, accounting for dispersion, we show that the double peak of the Jason-1 satellite observations are consistent with coseismic rupture of a splay fault of limited along-strike extent, located north of Simeulue Island. The doubly peaked morphology can be reproduced with co-activation of the subduction zone interface and the splay fault, which creates a seafloor uplift pattern with two distinct areas of uplift. The Jason-1 satellite is sensitive to a splay fault in this portion of the margin, whereas the TOPEX satellite would not be significantly affected by this uplift pattern. By back-projecting satellite observation points to the margin, we constrain the location of the proposed splay fault and find that it correlates with a bathymetric high. The aftershock locations, uplift of corals on Simeulue Island and a fault scarp on Pulau Salaut Besar are also consistent with the activation of a splay fault in the area delimited by the back-projection. Our work also shows that it is critical to fully capture gravity wave dispersion in order to represent features of the lead wave profile that may not be as well characterized by the shallow water (long-wavelength) model. It is also necessary to account for dispersion so as to precisely assess wavefront travel times; this leads us to conclude that the rupture must have reached very near to the trench and propagated with an updip rupture velocity of order 2.0?km/s or more.     

2004年12月26日印尼8.7级地震综述

本文给出了2004年12月26日印尼8．7级大地震的基本参数、区域构造背景、地震及海啸的损失情况及各国的应急反应,并提出了一些有益的建议。     

Tsunami Modeling to Validate Slip Models of the 2007 M w 8.0 Pisco Earthquake, Central Peru

Following the 2007, August 15th, M _w 8.0, Pisco earthquake in central Peru, Sladen et al. (J Geophys Res 115: B02405, 2010) have derived several slip models of this event. They inverted teleseismic data together with geodetic (InSAR) measurements to look for the co-seismic slip distribution on the fault plane, considering those data sets separately or jointly. But how close to the real slip distribution are those inverted slip models? To answer this crucial question, the authors generated some tsunami records based on their slip models and compared them to DART buoys, tsunami records, and available runup data. Such an approach requires a robust and accurate tsunami model (non-linear, dispersive, accurate bathymetry and topography, etc.) otherwise the differences between the data and the model may be attributed to the slip models themselves, though they arise from an incomplete tsunami simulation. The accuracy of a numerical tsunami simulation strongly depends, among others, on two important constraints: (i) A fine computational grid (and thus the bathymetry and topography data sets used) which is not always available, unfortunately, and (ii) a realistic tsunami propagation model including dispersion. Here, we extend Sladen’s work using newly available data, namely a tide gauge record at Callao (Lima harbor) and the Chilean DART buoy record, while considering a complete set of runup data along with a more realistic tsunami numerical that accounts for dispersion, and also considering a fine-resolution computational grid, which is essential. Through these accurate numerical simulations we infer that the InSAR-based model is in better agreement with the tsunami data, studying the case of the Pisco earthquake indicating that geodetic data seems essential to recover the final co-seismic slip distribution on the rupture plane. Slip models based on teleseismic data are unable to describe the observed tsunami, suggesting that a significant amount of co-seismic slip may have been aseismic. Finally, we compute the runup distribution along the central part of the Peruvian coast to better understand the wave amplification/attenuation processes of the tsunami generated by the Pisco earthquake.     

2010年智利大地震及历史地震活动与地质构造背景

2010年2月27日(当地时间)智利发生了8.8级地震,造成了严重的破坏和损失。该地震是典型的逆冲型地震,处于环太平洋地震带,是Nazca板块以每年8cm的汇聚速率俯冲于南美洲板块之下,使得该板块下部的应力积累到一定程度引发破裂的结果。历史地震分析表明,目前该地区可能开始一个新的大震活跃期,未来3～4年内可能还会发生一次8级以上的地震。     

南海地震与海啸

地震海啸的形成要具备3个条件:一是有深海盆地,可以容纳巨量海水;二是海底地形隆起与拗陷反差强烈;三是存在倾滑型活断层,可发生6级以上倾滑型的地震。查南海及其周边地形地貌,北西南三面都有宽阔的大陆架,中部又是平坦的深海平原,都不具备发生地震海啸的条件,惟独东侧马尼拉海沟才具备产生地震海啸的条件。南海地壳属于大洋型地壳与大陆型地壳之间的过度类型。其断裂构造非常发育,不同地段具有明显差异。北部为拉张型,南部为挤压型,西部为剪切型,东部为俯冲型,中部是扩张型。按断裂展布方向可分为NE向、NW向、EW向、SN向4组;按断裂切割深度,可分为岩石圈断裂、地壳断裂、基底断裂和盖层断裂。这些断裂多数为活动断裂,而东缘俯冲型断裂又是发震断裂。从地震分布、震源机制解分析,南海北、西、南以及中部都不具备引发地震海啸的条件,只有台南—菲律宾地震带东西两侧的贝尼奥夫带发生的倾滑型或具倾滑分量的走滑型6级以上地震,才有可能引发海啸,并可能对南海及我国东南沿海诸省以及港澳地区产生影响。     

Tsunami Source of the 2010 Mentawai, Indonesia Earthquake Inferred from Tsunami Field Survey and Waveform Modeling

The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 10²¹ Nm, which corresponded to M_w 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.     

永胜6.0级地震的地质构造背景及发震构造

阐述了永胜Ms6．0级地震震区的地震地质构造背景与构造应力场，结合本次地震的裂度分布几何形态、震源机制解、主余震震中分布和地表破坏等资料，讨论了地震的发震构造，认为程海断裂宾川－金沙江段是该地震的发震断理解。程海断裂宾川－金沙江段以左旋走滑活动为主，兼具正断层性质。     

Field Survey of the March 28, 2005 Nias-Simeulue Earthquake and Tsunami

On the evening of March 28, 2005 at 11:09?p.m. local time (16:09 UTC), a large earthquake occurred offshore of West Sumatra, Indonesia. With a moment magnitude (M _w) of 8.6, the event caused substantial shaking damage and land level changes between Simeulue Island in the north and the Batu Islands in the south. The earthquake also generated a tsunami, which was observed throughout the source region as well as on distant tide gauges. While the tsunami was not as extreme as the tsunami of December 26th, 2004, it did cause significant flooding and damage at some locations. The spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts.     

Expansion rate and geometry of floating vegetation mats on the margins of thermokarst lakes,northern Seward Peninsula,Alaska, USA

Investigations on the northern Seward Peninsula in Alaska identified zones of recent (<50 years) permafrost collapse that led to the formation of floating vegetation mats along thermokarst lake margins. The occurrence of floating vegetation mat features indicates rapid degradation of near‐surface permafrost and lake expansion. This paper reports on the recent expansion of these collapse features and their geometry is determined using geophysical and remote sensing measurements. The vegetation mats were observed to have an average thickness of 0.57 m and petrophysical modeling indicated that gas content of 1.5–5% enabled floatation above the lake surface. Furthermore, geophysical investigation provides evidence that the mats form by thaw and subsidence of the underlying permafrost rather than terrestrialization. The temperature of the water below a vegetation mat was observed to remain above freezing late in the winter. Analysis of satellite and aerial imagery indicates that these features have expanded at maximum rates of 1–2 m yr^‐1 over a 56 year period. Including the spatial coverage of floating ‘thermokarst mats’ increases estimates of lake area by as much as 4% in some lakes. Copyright © 2011 John Wiley & Sons, Ltd.     

1668年中国郯城8.5级巨震在韩半岛的地震影响区及地震海啸

16 6 8年 7月 2 5日中国山东省郯城MS8 5大地震是中国东部地区发生的最大的历史地震 ,有感半径 80 0多公里 ,50多万平方公里范围内的 1 50多个州县遭受不同程度的破坏。山东省郯城、沂州、莒州破坏最重 ,历史记载城廓、公廨、官民庐舍、庙宇等一时尽毁 ,并伴有大规模的山崩地裂、地陷、涌水喷沙等现象 ,历史记载共压毙 5万余人。该震极震区几何中心在郯城 ,烈度达XI度以上 (国家地震局震害防御司 ,1 995)。该巨震影响范围不仅限于中国东部诸省 ,还跨越黄海 ,波及韩半岛的广大地区 ,而且在韩半岛西北海岸形成了海啸。1　韩国历史文献关于该…     

山西大同——阳高6.1级地震地下流体异常的再研究

在山西大同—阳高 1989年 6 .1级地震的震例总结中 (张肇诚 .中国震例 .北京 :地震出版社 ,2 0 0 0 ) ,共收集了 2 7项地下流体异常 ,经过对资料的整理研究 ,又发现了 2 0项。以这些异常为样本 ,研究了异常场的形态组合、空间展布与时间演变等特征 ,指出水位动态异常以下降型为主 ,水化异常以上升型为主 ,异常呈条带分布 ,是场源共同作用下形成的。     

印尼8.7级地震海啸灾害及应急救援

本文介绍了2004年12月26日发生在印度尼西亚苏门答腊岛近海的8．7级地震后引发的大规模海啸对东南亚国家造成的灾难的情况、各受灾国的应急响应、国际救援及中国国际救援队前往印尼班达亚齐开展救援行动的情况。     

Field Survey of Tsunami Effects in Sri Lanka due to the Sumatra-Andaman Earthquake of December 26, 2004

The December 26, 2004 Sumatra-Andaman earthquake that registered a moment magnitude (M_w) of 9.1 was one of the largest earthquakes in the world since 1900. The devastating tsunami that resulted from this earthquake caused more casualties than any previously reported tsunami. The number of fatalities and missing persons in the most seriously affected countries were Indonesia - 167,736, Sri Lanka - 35,322, India - 18,045 and Thailand - 8,212. This paper describes two field visits to assess tsunami effects in Sri Lanka by a combined team of Japanese and Sri Lankan researchers. The first field visit from December 30, 2004 – January 04, 2005 covered the western and southern coasts of Sri Lanka including the cities of Moratuwa, Beruwala, Bentota, Pereliya, Hikkaduwa, Galle, Talpe, Matara, Tangalla and Hambantota. The objectives of the first field visit were to investigate the damage caused by the tsunami and to obtain eyewitness information about wave arrival times. The second field visit from March 10–18, 2005 covered the eastern and southern coasts of Sri Lanka and included Trincomalee, Batticaloa, Arugam Bay, Yala National Park and Kirinda. The objectives of the second visit were mainly to obtain eyewitness information about wave arrival times and inundation data, and to take relevant measurements using GPS instruments.     

The 15 August 2007 Peru Earthquake and Tsunami: Influence of the Source Characteristics on the Tsunami Heights

The tsunami caused by the 2007 Peru earthquake (M_w 8.0) provoked less damage than by the seismic shaking itself (numerous casualties due to the earthquake in the vicinity of Pisco). However, it propagated across the Pacific Ocean and small waves were observed on one tide gauge in Taiohae Bay (Nuku Hiva, Marquesas, French Polynesia). We invert seismological data to recover the rupture pattern in two steps. The first step uses surface waves to find a solution for the moment tensor, and the second step uses body waves to compute the slip distribution in the source area. We find the slip distribution to consist of two main slip patches in the source area. The inversion of surface waves yields a scalar moment of 8.9 10²⁰ Nm, and body-wave inversion gives 1.4 10²¹ Nm. The inversion of tsunami data recorded on a single deep ocean sensor also can be used to compute a fault slip pattern (yielding a scalar moment of 1.1 10²¹ Nm). We then use these different sources to model the tsunami propagation across the Pacific Ocean, especially towards Nuku Hiva. While the source model taken from the body-wave inversion yields computed tsunami waves systematically too low with respect to observations (on the central Pacific Ocean DART buoy as on the Polynesian tide gauge), the source model established from the surface-wave inversion is more efficient to fit the observations, confirming that the tsunami is sensitive to the low frequency component of the source. Finally we also discuss the modeling of the late tsunami arrivals in Taiohae Bay using several friction coefficients for the sea bottom.