The Storegga tsunami along the Norwegian coast, its age and run up

The statigraphy in 25 coastal lakes shows that most of the Norwegian coastline was impacted by a large tsunami about 7200 ¹⁴C BP. The methodology has been to core a staircase of lake basins above the contemporary sea level in several areas and to map the tsunami deposit to its maximum elevation. The tsunami was identified in the sedimentary record as an erosional unconformity overlain by graded or massive sand with shell fragments, followed by redeposited organic detritus. The greatest recorded runup along the coast (10–11 m above high tide) is found in areas most proximal to the Storegga slide scar on the Norwegian continental slope (Sunnmøre). To the north and south, runup is less, about 6–7 m at Bjugn (250 km north of Sunnmøre) and about 3–5 m in Austrheim (200 km to the south of Sunnmerre). This runup pattern supports the suggestion that the tsunami was generated by the Second Storegga Slide. The recorded runup heights are consistent within and between the investigated areas, and imply that the tsunami wave was not significantly influenced by the local topography, suggesting a very long wave length. The mapped runup estimates are in good agreement with a numerical model of the tsunami generated by the Second Storegga slide, and indicate that the slide was a single major event rather than a set of smaller slides.     

The sediment-fill of Pago Pago Bay (Tutuila Island,American Samoa): New insights on the sediment record of past tsunamis

Extensive bathymetric and two-dimensional seismic surveys have been carried out and cores collected in Pago Pago Bay (Tutuila, American Samoa) in order to describe and gain a better understanding of the sediment fill of the bay, which was affected by the 2009 South Pacific Tsunami. Eight sedimentary units were identified over the volcanic bedrock. The basal transgressive unit displays retrograding onlaps towards the shore, whereas the overlying seven aggradational layers alternate between four draping units and three pinching out seaward units. ‘Core to seismic’ correlation reveals that draping units are composed of homogeneous silts, while pinching out units are dominated by very coarse coral fragments showing fresh cuts, mixed with Halimeda plates. The basal unit is attributed to transgressive sedimentation in response to flooding of the bay after the last glacial maximum, followed by the upper aggradational units corresponding to highstand sedimentation. The changeovers in these upper units indicate an alternation between low-energy silt units and high-energy coral debris units interpreted as tsunami-induced deposits. The ¹⁴C dating reveals that high-energy sedimentation units can last up to approximately 2000 years while low-energy sedimentation units can last up to approximately 1000 years. This alternation, deposited during the last highstand, may be explained by cycles of tectonic activity and quiescence of the Tonga Trench subduction, which is the main source of tsunamigenic earthquakes impacting the Samoan archipelago. In the uppermost silt unit, only the geochemical signature of the terrestrial input of the 2009 SPT backwash deposits was detected between 7 cm and 9 cm depth. Hence, Pago Pago Bay offers a unique sediment record of Holocene bay-fill under the impact of past tsunamis intermittently during the last 7000 years.     

Distribution Functions of Tsunami Wave Heights

The problem of describing the distribution functions of tsunami wave heights is discussed. Data on runup heights obtained in field surveys of several tsunamis for the last decade are used to calculate the empirical distribution functions. It is shown that the log-normal distribution describes the observed data well. This means that the irregular topography and coastline are major factors which influence the height distribution. The power distribution related with the geometric decay of the propagated wave is a good approximation for one event (Sulawesi, January 1, 1996) only. Results of a numerical simulation of the tsunami event in the Japan (East) Sea on July 12, 1993 are presented. It is shown that the computed wave height distribution, obtained by using the runup correction in the framework of nonlinear shallow-water theory, is in good agreement with the observed height distribution. Simulations are used to study the transformation of the distribution function on different distances from the source.     

The 3 June 1994 Java Tsunami: A Post-Event Survey of the Coastal Effects

The paper is a report of the field campaign undertaken by an international team (Italian, French and Indonesian) a few weeks after the occurrence of a tsunami invading the south-eastern coast of Java (Indonesia) and it complements the results of a concurrent field survey by Asian and USA researchers. The tsunamigenic earthquake occurred on 3 of June 1994 in the Indian Ocean about 200 km south of Java. The tsunami caused severe damage and claimed many victims in some coastal villages. The main purpose of the survey was to measure the inundation and the runup values as well as to ascertain the possible morphological changes caused by the wave attacks. Attention was particularly focussed on the most affected districts, that is Lumajang, Jember and Banyuwangi in Java, although also the districts of Negera, Tebanan and Denpasar in Bali were examined. The most severe damage was observed in the Banyuwangi district, where the villages of Rajekwesi, Pancer and Lampon were almost completely levelled by the violent waves. Most places were hit by three significant waves with documented wave height often exceeding 5 m. The maximum runup value (9.50 m) was measured at Rajekwesi, where also the most impressive erosion phenomena could be found. In contrast, only in one place of the neighbouring island of Bali was there a slight tsunami, the rest of the island being practically unaffected.     

Tsunami runup on steep slopes: How good linear theory really is

This is a study of the application of linear theory for the estimation of the maximum runup height of long waves on plane beaches. The linear theory is reviewed and a method is presented for calculating the maximum runup. This method involves the calculation of the maximum value of an integral, now known as the runup integral. Laboratory and numerical results are presented to support this method. The implications of the theory are used to reevaluate many existing empirical runup correlations. It is shown that linear theory predicts the maximum runup satisfactorily. This study demonstrates that it is now possible to match complex offshore wave-evolution algorithms with linear theory runup solutions for the purpose of obtaining realistic tsunami inundation estimates.     

印度洋地震海啸(2004-12-26)及其对中国的警示

2004年12月26日印度尼西亚苏门答腊岛西北近海发生ML9级强烈地震。地震的强度是100a来全球非常罕见的。地震引起了巨大海啸,浪高近10m,波及到东南亚、南亚和东非地区10多个国家,造成近30万人遇难。地震使印度尼西亚、泰国的部分岛屿发生了地形变化。海啸在受灾国留下了大片的盐碱地。苏门答腊板块边缘的一个长距离破裂带通过长时间积累,蓄积了巨大能量。这些能量在2004-12-26集中释放出来。导致了这次地震海啸的发生。地震海啸灾害本身规模巨大,发生异常突然,再加上受灾地区人员密集,缺乏海啸灾害逃生的知识和经验。印度洋沿岸国家没有海啸预警系统,是造成这次灾害巨大伤亡的原因。中国从台湾-海南岛一线的海区,存在地震海啸的可能性。因此应不断完善海啸预警系统,提高沿海地区建设工程的防灾抗灾标准,加强防波堤建设以及采取恢复红树林等生物工程措施,预防潜在的海啸灾害。     

Registration of the Simushir and Nevelsk tsunamis in the port of Kholmsk

The November 16, 2006, Simushir and August 2, 2007, Nevelsk tsunami records obtained by bottom pressure gauges in Kholmsk Bay are analyzed. The dominant role of the zero mode of eigen oscillations in the bay during the the wave field formation is shown: in the initial record interval (for the remote tsunami source) and 1.5 h after the first wave (for the nearly tsunami). Numerical modeling showed that the longer waves propagated toward Kholmsk in the case of the Nevelsk earthquake and they did not generate eigen oscillations of the bay. These oscillations were generated 1.5 h later when the shorter waves reflected from the Primorye coast arrived.     

The 1996 Sulawesi Tsunami

On 1 January, 1996 at 16:05 p.m. local time, an earthquake of magnitude M = 7.8 struck the central part of Sulawesi Island (Indonesia). It was accompanied by tsunami waves 2–4 m high. Nine people were killed and 63 were injured. A tsunami survey was conducted by Indonesian and Russian specialists. The measured tsunami runup heights and eyewitness accounts are reported and discussed. Historical data on the Sulawesi Island tsunamis are analysed and tsunami risk prediction in the central part of Sulawesi Island carried out for the first time.     

A new tsunami runup predictor

Natural Hazards - We introduce a new parameter, tsunami runup predictor (TRP), relating the accelerating phase of the wave to the length of the beach slope over which the wave is travelling. We...     

Identification of tsunami deposits considering the tsunami waveform: An example of subaqueous tsunami deposits in Holocene shallow bay on southern Boso Peninsula, Central Japan

This study proposes a tsunami depositional model based on observations of emerged Holocene tsunami deposits in outcrops located in eastern Japan. The model is also applicable to the identification of other deposits, such as those laid down by storms. The tsunami deposits described were formed in a small bay of 10–20-m water depth, and are mainly composed of sand and gravel. They show various sedimentary structures, including hummocky cross-stratification (HCS) and inverse and normal grading. Although, individually, the sedimentary structures are similar to those commonly found in storm deposits, the combination of vertical stacking in the tsunami deposits makes a unique pattern. This vertical stacking of internal structures is due to the waveform of the source tsunamis, reflecting: 1) extremely long wavelengths and wave period, and 2) temporal changes of wave sizes from the beginning to end of the tsunamis.

The tsunami deposits display many sub-layers with scoured and graded structures. Each sub-layer, especially in sandy facies, is characterized by HCS and inverse and normal grading that are the result of deposition from prolonged high-energy sediment flows. The vertical stack of sub-layers shows incremental deposition from the repeated sediment flows. Mud drapes cover the sub-layers and indicate the existence of flow-velocity stagnant stages between each sediment flow. Current reversals within the sub-layers indicate the repeated occurrence of the up- and return-flows.

The tsunami deposits are vertically divided into four depositional units, Tna to Tnd in ascending order, reflecting the temporal change of wave sizes in the tsunami wave trains. Unit Tna is relatively fine-grained and indicative of small tsunami waves during the early stage of the tsunami. Unit Tnb is a protruding coarse-grained and thickest-stratified division and is the result of a relatively large wave group during the middle stage of the tsunami. Unit Tnc is a fine alternation of thin sand sheets and mud drapes, deposited from waning waves during the later stage of the tsunami. Unit Tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout. Cyclic build up of these sub-layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays.     

Tsunami bore runup

Nearshore behaviors of tsunamis, specifically those formed as a single uniform bore, are investigated experimentally in a laboratory environment. The transition process from tsunami bore to runup is described by the momentum exchange process between the bore and the small wedge-shaped water body along the shore: the bore front itself does not reach the shoreline directly, but the large bore mass pushes the small, initially quiescent water in front of it. The fluid motions near the runup water line appear to be complex. The complex flow pattern must be caused by irregularities involved in the driving bore and turbulence advected into the runup flow. Those experimental results suggest that the tsunami actions at the shoreline involve significant mean kinetic energy together with violent turbulence. Even though the behaviors of bore motion were found to be different from those predicted by the shallow-water wave theory, the maximum runup height appears to be predictable by the theory if the value of the initial runup velocity is modified (reduced). Besides the friction effect, this reduction of the initial runup velocity must be related to the transition process as well as the highly interacting three-dimensional runup motion.     

Behavior of historic tsunamis of volcanic origin as revealed by onshore tsunami deposits

According to the old documents, two historic tsunamis of volcanic origin attacked Hokkaido, northern Japan. They are the 1640 Komagatake event which killed more than 700 people and the 1741 Oshima-Ohshima event which killed 1467 people. In order to obtain more information of these old tsunami disasters, we studied onshore tsunami deposits associated with these events. Tsunami deposits are identified by their sedimentary structure and granulometric characteristics. We traced the 1640 and 1741 tsunami deposits showing similar features at outcrops, by making pits or trenches. Minimum runup heights of these historic tsunamis were revealed by these tsunami deposit distributions. Trench survey is one of the best way to find and study onshore paleo-tsunami deposit     

Abiki oscillations in Sakitsu Bay,west Kyushu,Japan

Sakitsu and Yokaku bays in Amakusa in west Kyushu, Japan, experienced inundation damage in the February 2009 meteotsunami (Abiki) event. The oscillation characteristics of both bays are investigated by taking field measurements and conducting numerical experiments with regard to flood mitigation with the aim to reduce the flood impact during Abiki events. A continuous wavelet transform and bandpass filtering both of the pressure and water level indicated that a sequence of pressure disturbances, as small as 1.0 hPa, caused the large amplified oscillation within Sakitsu Bay. When a sequence of ocean long waves entered the bay, a surf beat evolved in the early stages. Subsequently, the sea level began to undergo large amplitude oscillations, and there was a secondary peak of oscillation with a period of around 24 min, as seen in both field measurements and numerical experiments. A surf beat with the period of 12 min formed in Yokaku Bay owing to the continuous incidence of ocean waves with period of 12 min, but its wave period was almost half of that of the natural period of the bay. This surf beat may have entered Sakitsu Bay with natural period of 11.8 min and caused large water-level fluctuations.     

The 1979 nice airport tsunami: mapping of the flood in Antibes

On 16 October 1979, a tsunami of a local origin hits the French Riviera around Nice, France, killing 8 people and generating important economic losses. Its impact was felt from Hyères to Menton, France. The main effect of this tsunami was flooding in the neighborhoods of La Salis and La Garoupe, Antibes, France. A synthesis of unpublished reports written in the context of an administrative investigation was conducted. Various archives were also consulted (newspapers, fire and rescue unit reports, insurance reports, etc.), and a field survey was organized in 2009 to record testimonies from the inhabitants who witnessed the flood in La Salis, Antibes, the area where the effects of the tsunami were the greatest. A geo-database of the neighborhood of La Salis was built using available aerial imagery, land cover data and digital terrain models, to reconstruct the surface of the flooded area as it was in 1979 and as it is now. Comparing precise testimonies and the 1979 topographic information available allowed the authors to precisely map the flood and to deduce the runup values which reached 3.5 m locally, with a maximal distance of flooding of 150 m inland. This paper provides modelers with precious information about the extent of flooding and the time sequence in order to reconstitute the propagation and flooding of the 16 October 1979 tsunami. This information highlights the fact that the French Riviera is a low hazard, but high vulnerability area.     

Changes in beach water table elevation during neap and spring tides on a sandy estuarine beach, Delaware Bay, New Jersey

A field investigation of temporal and spatial changes in wind and wave characteristics, runup and beach water table elevation was conducted on the foreshore of an estuarine beach in Delaware Bay during neap (April 9, 1995) and spring (April 16, 1995) tides under low wave-energy conditions. The beach has a relatively steep, sandy foreshore and semi-diurnal tides with a mean range of 1.6 m and a mean spring range of 1.9 m. Data from a pressure transducer placed on the low tide terrace reveal a rate of rise and fall of the water level on April 16 of 0.09 mm s⁻¹ resulting in a steeper tidal curve than the neap tide on April 9. Data from three pressure transducers placed in wells in the intertidal foreshore reveal that the landward slope of the water table during the rising neap tide was lower than the slope during spring tide, and there was a slower rate of fall of the beach water table relative to the fall of the tide. Wave heights were lower on April 9 (significant height from 17.1 min records <0.16 m). The water table elevation was 0.08 m higher than the water in the bay at the time of high water, when maximum runup elevation was 0.29 m above high water and maximum runup width was 2.0 m. The elevation of the water table was 0.13 m higher than the maximum elevation of water level in the bay 74 min after high water, when wave height was 0.12 m and wave period was 2.7 s. The use of mean bay water level at high tide will underpredict the elevation of the water table in the beach, and demarcation of biological sampling stations across the intertidal profile based on mean tide conditions will not accurately reflect the water content of the sandy beach matrix.     

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.     

Truncated flame structures within a deposit of the Indian Ocean Tsunami: evidence of syn‐sedimentary deformation

This study reveals the three‐dimensional morphology and syn‐sedimentary formation processes of a deformation structure termed ‘truncated flame structures’ which is found in a terrestrial tsunami deposit in southern Thailand that formed during the 2004 Indian Ocean Tsunami. The structure was found at the boundary between a lower fine‐grained layer and an upper coarse‐grained layer that are related to two runup events. In order to confirm the morphology of the structure, the authors excavated two trenches and an opencast pit. When viewed in a cross‐section oriented parallel to the direction of the runup current, the deformed boundary has an irregularly bulging profile, similar to that observed in flame structures. The protruding structures are inclined towards the downstream direction of the runup current, and are truncated horizontally along their upper surface by parallel laminations in the overlying layer. When viewed in a cross‐section oriented perpendicular to the current direction, it appears that parts of the upper layer descend into the lower layer as lobate masses. In places, these masses are completely detached from the main part of the upper layer, forming circular or elliptical shapes. The contact between the lower layer and the main part of the upper layer is a planar truncation surface. Opencast excavation of the contact surface revealed that the deformed structures have flat, sinuous horseshoe crests that open in a downstream direction. It is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure. Moreover, the observations made in this study indicate the syn‐sedimentary development of the structure: deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer. Truncated flame structures can be used as a criterion in identifying the syn‐sedimentary deformation of substrate: the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate. As in the present case, the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis, rather than other events such as storm surges or flooding.     

Tsunami-induced scour at coastal roadways: a laboratory study

Coastal roads are lifelines for bringing emergency personnel and equipment into affected areas after tsunamis, thus careful thought should be given to how to make roadways safer from tsunamis. Scouring at roadways is the primary damage caused by tsunamis; however, tsunami-induced scouring and beach erosion are less understood compared to tsunami runup and tsunami inundation. A set of laboratory experiments are reported in this study on tsunami-induced scour at a road model situated on a sandy beach. Our experiments showed that the distance between the shoreline and a roadway, which varies with tides, was a key factor affecting the scour depth at the road. Having the coastal road at about half of the inundation distance is not the most ideal location. The depth of road embedment did not affect the scour depth in our experiments. It was also found that for typical tsunamis, the scour depth is unlikely to reach its equilibrium stage. The information reported in this study is useful for local authorities to assess potential tsunami damage of roads and to have a better plan for tsunami disaster relief.     

Fish and blue crab assemblage structure in a U.S. mid Atlantic coastal lagoon complex

Variability in assemblages of organisms in contiguous lagoons is dependent upon component bays and their connections to the ocean and terrestrial watersheds. Fish and blue crab assemblage structure of Maryland's coastal lagoon complex, which consists of Assawoman, Isle of Wight, Sinepuxent, and Chincoteague Bays, was analyzed for spatial and seasonal patterns for the period 1991–2002. Nonmetric multidimensional scaling ordinated sites from a Maryland state trawl survey into discrete groups associated with each embayment. Dominant species includedCallinectes sapidus, Anchoa mitchilli, Leiostomous xanthurus, Bairdiella chrysoura, andBrevoortia tyramus. The relative abundance of these and other dominant species were significantly higher in the two bays north of the ocean inlet than in bays south of the inlet. Ninety-two species were identified in the survey, with total species richness highest in the southern-most bay (Chincoteague: S=83) and lowest in the northern most bay (Assawoman: S=59). On a catch per unit effort basis, the northern two bays were more diverse and productive. These bays were most affected by anthropogenic eutrophication, but also exhibited higher connectivity to the ocean inlet. There was clear seasonality in assemblage structure with peak abundance and diversity in the summer compared to spring and fall. Factors that influenced seasonal and spatial structure of Maryland's coastal lagoon complex included temperature, degree of eutrophication, and proximity to oceanic exchange. The arrangement of the bays in their exposure to oceanic and watershed influences specify that habitat management actions should occur at a bay-level scale rather than across the lagoon complex.     

Source mechanism of the tsunamis of 19 and 21 September 1985, in Mexico

The major earthquake measuring 8.1 on the Richter scale which struck the west coast of Mexico on Thursday 19 September 1985, generated a small tsunami. A major aftershock on 21 September, with a magnitude of 7.5 also produced a small tsunami. Both tsunamis propagated across the Pacific and were recorded by several tide stations in Central America, Colombia, Ecuador, French Polynesia, Samoa, and Hawaii. No reports of damage were received from any of the stations, and only minor damage due to the first tsunami was reported from the source region.A survey was made by the International Tsunami Information Center (ITIC) of the coastal area affected, from Manzanillo to Zihuatanejo. Tsunami runup measurements were taken and interviews with local residents in the coastal areas were conducted.A source mechanism study of the tsunamis was undertaken using seismic and geologic data and empirical relationships. Earthquake and tsunami energies were estimated and the tsunami genertion areas defined.The earthquake energies were estimated to be 5.61 × 10²⁴ erg for the 19 September event and 9.9 × 10²³ erg for the 21 September event. Tsunami energies were estimated to be 0.7 × 10²⁰ erg for the first event and 0.56 × 10²⁰ erg for the second event. The source area of the first tsunami was determined to be approximately one-half of the earthquake source area, or approximately 7500 km², while the source area of the second tsunami was estimated to be equal to the earthquake area.The relatively small tsunamis generated by these large earthquakes are attributed to the shallow angle of subduction of the Cocos plate underneath the North American plate for this particular region, and to the small vertical component of crustal displacements. However, the angle of subduction increases further south and local earthquakes from that area have the potential of producing large tsunamis on the west coast of Mexico.This paper was presented at the 4th International Symposium on Natural and Man-made Coastal Hazards held in Ensenada, Mexico, August 1988.