Thai Evidence for Recurrent Indian Ocean Tsunamis of the Last 3,000 Years
ABSTRACT Late Holocene tsunamis probably like the one in 2004 have attacked Thailand's An... more ABSTRACT Late Holocene tsunamis probably like the one in 2004 have attacked Thailand's Andaman Sea coast at irregular intervals of less than 1,000 years on average. The 2004 tsunami ended a recurrence interval ~600 years long. Such geology could have foretold the 2004 Indian Ocean tsunami. These interpretations, all preliminary, are based on stratigraphic reconnaissance of marshy swales between grassy beach ridges of Ko Phra Thong, an island 125 km north of Phuket. Pre-2004 tsunamis best explain several properties of sand lentils that are intercalated with freshwater peaty soils of the swales: SETTING. The island's beach-ridge plain, which extends 3 km inland and 15 km coastwise, was mostly overrun by the 2004 tsunami, which coated much of it with sand. By contrast, river floods do not reach the plain because tidal inlets separate Ko Phra Thong from the mainland. Storm surges of recent decades scarcely penetrated the beach-ridge plain. Storm runoff from the beach-ridge crests, which gently rise just 1-2 m above the swales, is limited by permeable soils; the ridges lack rills and sheetwash fans. THICKNESS. Like the 2004 tsunami deposit, three of the sand lentils maintain thicknesses of 5-20 cm along a cross-swale extent of 20-40 m, as seen in correlated pits and a trench 0.5 km inland from the present beach. ARCHITECTURE. Along this cross section and another nearby, each of the sand lentils extends farther up the seaward flank of the swale than up the landward side. The 2004 sand sheet is thick on the seaward flank and thin on the landward flank. FREQUENCY. In a sequence of three sand lentils, the youngest is close to 550-700 years old and the two earlier ones probably formed between 2,000 and 2,800 years ago. These estimates are based on radiocarbon dating of leaves and bark in buried soils and of marine shells below the lowest peat. RECYCLING. Two of the lentils contain leaf fragments centuries older than the time of deposition. The discordance is consistent with tsunami-induced scour of the beds of tidal inlets. Puzzles about the sand lentils include: MICROFOSSILS. Sand lentils examined thus far contain few calcareous foraminiferal tests and no diatom valves. Both these fossil types are abundant in Ko Phra Thong's 2004 tsunami deposits. In addition, the fossils of freshwater diatoms have been found in the peaty soils of the swales, both beneath the 2004 deposits and beneath the underlying sand lentils as well. Did tropical diagenesis erase fossil diatoms from the sand lentils? INUNDATION. Along the cross sections studied thus far, the maximum flow depth in 2004 probably exceeded 10 m. Do the sand lentils represent similar inundation? TSUNAMI SOURCES. In one of the cross sections, traces of a sand bed 1-2 cm thick are preserved between two of the sand lentils. Does the thin bed signify a tsunami source little larger than that of 1881, while the thicker sand lentils signify full-length Sumatra-Andaman ruptures?
Paleotsunamis in the Middle Kuril Islands--Implications for a Seismic Gap (and in View of Recent Events)
Two great earthquakes occurred in the middle Kurils on 15 Nov 2006 (Mw 8.3) and 13 Jan 2007 (Mw 8... more Two great earthquakes occurred in the middle Kurils on 15 Nov 2006 (Mw 8.3) and 13 Jan 2007 (Mw 8.1). These earthquakes were the first big events in the short (< 300-yr) historical catalogue of this segment of the Kuril- Kamchatka subduction zone. This segment had been identified as a "seismic gap," and some researchers suggested that in this gap,
Tsunami erosion: Geomorphology before and after the 15 Nov 2006 tsunami in the middle Kuril Islands, Russia
Because the 15 Nov 2006 middle Kuril Island earthquake (Mw 8.3) and tsunami occurred between two ... more Because the 15 Nov 2006 middle Kuril Island earthquake (Mw 8.3) and tsunami occurred between two field expeditions of the Kuril Biocomplexity Project, we have detailed topographic profiles and photographs from 3 months before and 9 months after the event. Thus, we are in the position to define tsunami-induced changes in coastal geomorphology both quantitatively and qualitatively. The locations where
The ability to measure, predict, and compute tsunami flow velocities is of importance in risk ass... more The ability to measure, predict, and compute tsunami flow velocities is of importance in risk assessment and hazard mitigation. Substantial damage can be done by high velocity flows, particularly in harbors and bays, even when the wave height is small. Moreover, advancing the study of sediment transport and tsunami deposits depends on the accurate interpretation and modeling of tsunami flow velocities and accelerations. Until recently, few direct measurements of tsunami velocities existed to compare with model results. During the 11 March 2011 Tohoku Tsunami 328 current meters were in place around the Hawaiian Islands, USA, that captured time series of water velocity in 18 locations, in both harbors and deep channels, at a series of depths. We compare several of these velocity records against numerical simulations performed using the GeoClaw numerical tsunami model, based on solving the depth-averaged shallow water equations with adaptive mesh refinement, to confirm that this model can accurately predict velocities at nearshore locations. Model results demonstrate tsunami current velocity is more spatially variable than wave form or height and therefore may be a more sensitive variable for model validation.
Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow con... more Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow conditions during the tsunami. The tsunami deposit consists of single or multiple graded beds. Diatom assemblages in the lowermost part of the deposit predominantly comprise beach and subtidal species. In the middle part of the deposit, the assemblages are dominated by marine plankton with increasing finer fractions. A mixed assemblage of freshwater, brackish, and marine species occupies the uppermost part of the deposit. Changes in flow conditions during the tsunami can explain these diatom assemblage variations. During fast current velocities, medium sand is deposited; only beach and subtidal diatoms that live attached to the sand can be incorporated into the tsunami deposit under these flow conditions. It is difficult for diatoms in suspension to settle out under fast current velocities. With decreasing current velocities, marine plankton can settle out of the water column .Finally, duri...
Bulletin of the Seismological Society of America, 2012
Stratigraphic evidence for coseismic uplift, a tsunami, and a sandy debris flow linked to the A.D... more Stratigraphic evidence for coseismic uplift, a tsunami, and a sandy debris flow linked to the A.D. 900-930 Seattle-fault-zone earthquake and subsequent submergence is present at Gorst at the terminus of Sinclair Inlet, Washington. This study indicates that at least 3 m of uplift preceded a tsunami followed by a sandy debris flow. Though the Seattle and Tacoma fault zones ruptured within the error of ages of the tsunami deposit, model simulations indicate the Seattle fault generates an order of magnitude larger tsunami in the vicinity of the field area than the Tacoma fault and is the more likely generator of the tsunami. Simulations indicate amplitude from a Seattle-fault-zone-generated wave train was 4-5 m, and stratigraphy shows the tsunami left a sandy deposit. Soft-sediment deformation narrows the time window for the debris flow to the hours to months after the tsunami. Slope failure in unconsolidated glacial sands likely initiated a debris flow that surged at least 2 km down Gorst Creek valley and left a more than 40-cm-thick deposit along the creek and in the wetlands. Submergence of a Thuja plicata (western red cedar) swamp into the intertidal zone indicates at least 1.5 m of submergence in the last 1100 years. This submergence indicates uplift on nearby marine terraces associated with the Seattle fault zone was likely higher, and the A.D. 900-930 earthquake was potentially larger, than previously recognized.
1,100 years after an earthquake: modification of the earthquake record by submergence, Puget Lowland, Washington State
ABSTRACT Crustal faults may pose a complicated story for earthquake reconstruction. In some cases... more ABSTRACT Crustal faults may pose a complicated story for earthquake reconstruction. In some cases, regional tectonic strain overprints the record of coseismic land-level changes. This study looks at the record of earthquakes at two sites in the Puget Lowland, Gorst and the Skokomish delta, and how post-earthquake submergence modified the paleoseismic records. The Puget Lowland is the slowly subsiding forearc basin of the northern Cascadia subduction zone. A series of active thrust faults cross this lowland. Several of these faults generated large (M7+) earthquakes, about 1,100 years ago and both field sites have submerged at least 1.5 m since that time. This submergence masked the geomorphic record of uplift in some areas, resulting in a misreading of the zone of earthquake deformation and potential misinterpretation of the underlying fault structure. Earthquakes ~1,100 years ago uplifted both field localities and altered river dynamics. At Gorst, a tsunami and debris flow accompanied uplift of at least 3 m by the Seattle fault. The increased sediment load resulted in braided stream formation for a period after the earthquake. At the Skokomish delta, differential uplift trapped the river on the eastern side of the delta for the last 1,100 years resulting in an asymmetric intertidal zone, 2-km wider on one side of the delta than the other. The delta slope or submergence may contribute to high rates of flooding on the Skokomish River. Preliminary results show the millennial scale rates of submergence vary with the southern Puget Lowland submerging at a faster rate than the northern Puget Lowland. This submergence complicates the reconstruction of past earthquakes and renders assessment of future hazards difficult for those areas that are based on uplifted marine platforms and other coastal earthquake signatures in several ways. 1) Post-earthquake submergence reduces the apparent uplift of marine terraces. 2) Submergence makes zones of earthquake deformation appear narrower. 3) The record of older earthquakes may have been submerged and destroyed by coastal processes. 4) Submergence leads to the burial and destruction of coastal deposits, e.g. tsunami deposits. 5) In areas where uplift alters drainage patterns, submergence may simply obscure the changes.
Tsunami modeling of multiple earthquake sources from the 2011 Tohoku event using GeoClaw
ABSTRACT Determining reliable methods for computing the initial tsunami waveform produced by an e... more ABSTRACT Determining reliable methods for computing the initial tsunami waveform produced by an earthquake will strengthen the ability of tsunami models to both hindcast and forecast potential tsunami hazards. The dense network of instrumental records of the 2011 Tohoku earthquake- including seismometers, GPS receivers, tide gauges, and DART buoys-enabled an unprecedented number of solutions of the earthquake's rupture pattern to be computed. The Tohoku earthquake thus allows us to investigate how complex earthquake ruptures affect tsunami generation, with the aim of resolving the components of the earthquake rupture that dominate tsunami generation. We investigate differences in the farfield and open ocean tsunami waveforms based on a number of proposed earthquake rupture solutions. We compare tsunami waveforms simulated by the tsunami model GeoClaw at a number of locations, including DART buoys in the NW Pacific and tide gauges in California. GeoClaw is a finite volume numerical model using shallow-water-wave equations and adaptive-grid refinement to simulate tsunami waves across bathymetry and onto topography. Our earthquake input files are generated by combining the seafloor deformation of multiple subfaults as predicted by Okada's equations. GeoClaw is an open source code available at http://www.clawpack.org/geoclaw/ The initial seafloor deformation is the key input for comparison between potential tsunami sources and actual measurements. At the DART buoys closest to the earthquake, the overall wavelengths of simulated tsunami oscillations are very similar for the different earthquake rupture models. The primary differences between simulated tsunamis are the amplitude and wavelength of the initial wave. Sources with extensive rupture perpendicular to strike tend to have a longer initial wavelength than the recorded waveform, while sources with rupture primarily near the trench arrive too early at some of the DART buoys. Tsunami measurements in California, far from the Tohoku earthquake, can also be used to distinguish between sources based on waveform characteristics. In Crescent City, California, resonance in the harbor results in the first six waves being significant, allowing for the comparison of tsunami simulations to a long waveform. Most simulated tsunamis have similar wavelengths and general waveform to the recorded tide gauge observation, though they differ in the timing of the first arrival and the amplitude of the waves. Work to compare simulated tsunamis from multiple sources to tide gauges in other locations is ongoing.
Geomorphology of beach ridges and Holocene terraces on Kamchatka: A complex interplay of tectonics, volcanism and coastal processes
Despite decades of analysis, the origin of beach ridges remains debatable, and coastal morphotect... more Despite decades of analysis, the origin of beach ridges remains debatable, and coastal morphotectonics an open field. On the eastern coast of Kamchatka, along about 700 km of coastline (northwest Pacific and southwest Bering Sea), we have measured accumulative Holocene coastal profiles spanning a range of conditions including variable tectonics (co-seismic and longer term), wave climate, sea ice, and sediment
ABSTRACT A sand layer from a predecessor to the 2004 Indian Ocean tsunami underlies a freshwater ... more ABSTRACT A sand layer from a predecessor to the 2004 Indian Ocean tsunami underlies a freshwater marsh on Phra Thong Island, Phang Nga Province, Thailand. At this marsh, about 300 meters from the sea, the 2004 tsunami left a sand layer about 13 cm thick on top of a peaty soil. The previous tsunami deposit, of similar thickness, rests on another peaty soil about 40 cm below present ground surface. It probably correlates with a pre-2004 tsunami deposit previously reported from Phra Thong Island in a web posting by Shigehiro Fujino. Observed in trenches and cores, the pre-2004 deposit begins with a razor-sharp contact with the underlying soil. The sand itself contains no fewer than 6 layers, all horizontal, defined by differences in particle size (fine sand and very fine sand) and by detrital plant fragments. We also noticed pebble-size clasts of peaty soil. These observations come from the vicinity of UTM coordinates 418975E, 1009496N, zone 47. Many of us participated in previous, unsuccessful attempts to find pre-2004 tsunami deposits in Thailand. We hunted for sand sheets between Phuket to the south and Kho Khao Island to the north, on beach-ridge plains disturbed by tin mining and in mangrove swamps. We also checked pristine, grassy beach-ridge plains of Phra Thong Island, the next island north of Kho Khao. None of these environments offer both a host deposit that contrasts with tsunami-laid sand and a lack of disturbance by tin miners, mud lobsters, and real-estate developers.
Bourgeois, J.; Pinegina, T.; Martin, M. E.; Kravchunovskaya, E. American Geophysical Union, Fall ... more Bourgeois, J.; Pinegina, T.; Martin, M. E.; Kravchunovskaya, E. American Geophysical Union, Fall Meeting 2005, abstract #T11A-0360
Thai Evidence for Recurrent Indian Ocean Tsunamis of the Last 3,000 Years
ABSTRACT Late Holocene tsunamis probably like the one in 2004 have attacked Thailand's An... more ABSTRACT Late Holocene tsunamis probably like the one in 2004 have attacked Thailand's Andaman Sea coast at irregular intervals of less than 1,000 years on average. The 2004 tsunami ended a recurrence interval ~600 years long. Such geology could have foretold the 2004 Indian Ocean tsunami. These interpretations, all preliminary, are based on stratigraphic reconnaissance of marshy swales between grassy beach ridges of Ko Phra Thong, an island 125 km north of Phuket. Pre-2004 tsunamis best explain several properties of sand lentils that are intercalated with freshwater peaty soils of the swales: SETTING. The island's beach-ridge plain, which extends 3 km inland and 15 km coastwise, was mostly overrun by the 2004 tsunami, which coated much of it with sand. By contrast, river floods do not reach the plain because tidal inlets separate Ko Phra Thong from the mainland. Storm surges of recent decades scarcely penetrated the beach-ridge plain. Storm runoff from the beach-ridge crests, which gently rise just 1-2 m above the swales, is limited by permeable soils; the ridges lack rills and sheetwash fans. THICKNESS. Like the 2004 tsunami deposit, three of the sand lentils maintain thicknesses of 5-20 cm along a cross-swale extent of 20-40 m, as seen in correlated pits and a trench 0.5 km inland from the present beach. ARCHITECTURE. Along this cross section and another nearby, each of the sand lentils extends farther up the seaward flank of the swale than up the landward side. The 2004 sand sheet is thick on the seaward flank and thin on the landward flank. FREQUENCY. In a sequence of three sand lentils, the youngest is close to 550-700 years old and the two earlier ones probably formed between 2,000 and 2,800 years ago. These estimates are based on radiocarbon dating of leaves and bark in buried soils and of marine shells below the lowest peat. RECYCLING. Two of the lentils contain leaf fragments centuries older than the time of deposition. The discordance is consistent with tsunami-induced scour of the beds of tidal inlets. Puzzles about the sand lentils include: MICROFOSSILS. Sand lentils examined thus far contain few calcareous foraminiferal tests and no diatom valves. Both these fossil types are abundant in Ko Phra Thong's 2004 tsunami deposits. In addition, the fossils of freshwater diatoms have been found in the peaty soils of the swales, both beneath the 2004 deposits and beneath the underlying sand lentils as well. Did tropical diagenesis erase fossil diatoms from the sand lentils? INUNDATION. Along the cross sections studied thus far, the maximum flow depth in 2004 probably exceeded 10 m. Do the sand lentils represent similar inundation? TSUNAMI SOURCES. In one of the cross sections, traces of a sand bed 1-2 cm thick are preserved between two of the sand lentils. Does the thin bed signify a tsunami source little larger than that of 1881, while the thicker sand lentils signify full-length Sumatra-Andaman ruptures?
Paleotsunamis in the Middle Kuril Islands--Implications for a Seismic Gap (and in View of Recent Events)
Two great earthquakes occurred in the middle Kurils on 15 Nov 2006 (Mw 8.3) and 13 Jan 2007 (Mw 8... more Two great earthquakes occurred in the middle Kurils on 15 Nov 2006 (Mw 8.3) and 13 Jan 2007 (Mw 8.1). These earthquakes were the first big events in the short (< 300-yr) historical catalogue of this segment of the Kuril- Kamchatka subduction zone. This segment had been identified as a "seismic gap," and some researchers suggested that in this gap,
Tsunami erosion: Geomorphology before and after the 15 Nov 2006 tsunami in the middle Kuril Islands, Russia
Because the 15 Nov 2006 middle Kuril Island earthquake (Mw 8.3) and tsunami occurred between two ... more Because the 15 Nov 2006 middle Kuril Island earthquake (Mw 8.3) and tsunami occurred between two field expeditions of the Kuril Biocomplexity Project, we have detailed topographic profiles and photographs from 3 months before and 9 months after the event. Thus, we are in the position to define tsunami-induced changes in coastal geomorphology both quantitatively and qualitatively. The locations where
The ability to measure, predict, and compute tsunami flow velocities is of importance in risk ass... more The ability to measure, predict, and compute tsunami flow velocities is of importance in risk assessment and hazard mitigation. Substantial damage can be done by high velocity flows, particularly in harbors and bays, even when the wave height is small. Moreover, advancing the study of sediment transport and tsunami deposits depends on the accurate interpretation and modeling of tsunami flow velocities and accelerations. Until recently, few direct measurements of tsunami velocities existed to compare with model results. During the 11 March 2011 Tohoku Tsunami 328 current meters were in place around the Hawaiian Islands, USA, that captured time series of water velocity in 18 locations, in both harbors and deep channels, at a series of depths. We compare several of these velocity records against numerical simulations performed using the GeoClaw numerical tsunami model, based on solving the depth-averaged shallow water equations with adaptive mesh refinement, to confirm that this model can accurately predict velocities at nearshore locations. Model results demonstrate tsunami current velocity is more spatially variable than wave form or height and therefore may be a more sensitive variable for model validation.
Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow con... more Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow conditions during the tsunami. The tsunami deposit consists of single or multiple graded beds. Diatom assemblages in the lowermost part of the deposit predominantly comprise beach and subtidal species. In the middle part of the deposit, the assemblages are dominated by marine plankton with increasing finer fractions. A mixed assemblage of freshwater, brackish, and marine species occupies the uppermost part of the deposit. Changes in flow conditions during the tsunami can explain these diatom assemblage variations. During fast current velocities, medium sand is deposited; only beach and subtidal diatoms that live attached to the sand can be incorporated into the tsunami deposit under these flow conditions. It is difficult for diatoms in suspension to settle out under fast current velocities. With decreasing current velocities, marine plankton can settle out of the water column .Finally, duri...
Bulletin of the Seismological Society of America, 2012
Stratigraphic evidence for coseismic uplift, a tsunami, and a sandy debris flow linked to the A.D... more Stratigraphic evidence for coseismic uplift, a tsunami, and a sandy debris flow linked to the A.D. 900-930 Seattle-fault-zone earthquake and subsequent submergence is present at Gorst at the terminus of Sinclair Inlet, Washington. This study indicates that at least 3 m of uplift preceded a tsunami followed by a sandy debris flow. Though the Seattle and Tacoma fault zones ruptured within the error of ages of the tsunami deposit, model simulations indicate the Seattle fault generates an order of magnitude larger tsunami in the vicinity of the field area than the Tacoma fault and is the more likely generator of the tsunami. Simulations indicate amplitude from a Seattle-fault-zone-generated wave train was 4-5 m, and stratigraphy shows the tsunami left a sandy deposit. Soft-sediment deformation narrows the time window for the debris flow to the hours to months after the tsunami. Slope failure in unconsolidated glacial sands likely initiated a debris flow that surged at least 2 km down Gorst Creek valley and left a more than 40-cm-thick deposit along the creek and in the wetlands. Submergence of a Thuja plicata (western red cedar) swamp into the intertidal zone indicates at least 1.5 m of submergence in the last 1100 years. This submergence indicates uplift on nearby marine terraces associated with the Seattle fault zone was likely higher, and the A.D. 900-930 earthquake was potentially larger, than previously recognized.
1,100 years after an earthquake: modification of the earthquake record by submergence, Puget Lowland, Washington State
ABSTRACT Crustal faults may pose a complicated story for earthquake reconstruction. In some cases... more ABSTRACT Crustal faults may pose a complicated story for earthquake reconstruction. In some cases, regional tectonic strain overprints the record of coseismic land-level changes. This study looks at the record of earthquakes at two sites in the Puget Lowland, Gorst and the Skokomish delta, and how post-earthquake submergence modified the paleoseismic records. The Puget Lowland is the slowly subsiding forearc basin of the northern Cascadia subduction zone. A series of active thrust faults cross this lowland. Several of these faults generated large (M7+) earthquakes, about 1,100 years ago and both field sites have submerged at least 1.5 m since that time. This submergence masked the geomorphic record of uplift in some areas, resulting in a misreading of the zone of earthquake deformation and potential misinterpretation of the underlying fault structure. Earthquakes ~1,100 years ago uplifted both field localities and altered river dynamics. At Gorst, a tsunami and debris flow accompanied uplift of at least 3 m by the Seattle fault. The increased sediment load resulted in braided stream formation for a period after the earthquake. At the Skokomish delta, differential uplift trapped the river on the eastern side of the delta for the last 1,100 years resulting in an asymmetric intertidal zone, 2-km wider on one side of the delta than the other. The delta slope or submergence may contribute to high rates of flooding on the Skokomish River. Preliminary results show the millennial scale rates of submergence vary with the southern Puget Lowland submerging at a faster rate than the northern Puget Lowland. This submergence complicates the reconstruction of past earthquakes and renders assessment of future hazards difficult for those areas that are based on uplifted marine platforms and other coastal earthquake signatures in several ways. 1) Post-earthquake submergence reduces the apparent uplift of marine terraces. 2) Submergence makes zones of earthquake deformation appear narrower. 3) The record of older earthquakes may have been submerged and destroyed by coastal processes. 4) Submergence leads to the burial and destruction of coastal deposits, e.g. tsunami deposits. 5) In areas where uplift alters drainage patterns, submergence may simply obscure the changes.
Tsunami modeling of multiple earthquake sources from the 2011 Tohoku event using GeoClaw
ABSTRACT Determining reliable methods for computing the initial tsunami waveform produced by an e... more ABSTRACT Determining reliable methods for computing the initial tsunami waveform produced by an earthquake will strengthen the ability of tsunami models to both hindcast and forecast potential tsunami hazards. The dense network of instrumental records of the 2011 Tohoku earthquake- including seismometers, GPS receivers, tide gauges, and DART buoys-enabled an unprecedented number of solutions of the earthquake's rupture pattern to be computed. The Tohoku earthquake thus allows us to investigate how complex earthquake ruptures affect tsunami generation, with the aim of resolving the components of the earthquake rupture that dominate tsunami generation. We investigate differences in the farfield and open ocean tsunami waveforms based on a number of proposed earthquake rupture solutions. We compare tsunami waveforms simulated by the tsunami model GeoClaw at a number of locations, including DART buoys in the NW Pacific and tide gauges in California. GeoClaw is a finite volume numerical model using shallow-water-wave equations and adaptive-grid refinement to simulate tsunami waves across bathymetry and onto topography. Our earthquake input files are generated by combining the seafloor deformation of multiple subfaults as predicted by Okada's equations. GeoClaw is an open source code available at http://www.clawpack.org/geoclaw/ The initial seafloor deformation is the key input for comparison between potential tsunami sources and actual measurements. At the DART buoys closest to the earthquake, the overall wavelengths of simulated tsunami oscillations are very similar for the different earthquake rupture models. The primary differences between simulated tsunamis are the amplitude and wavelength of the initial wave. Sources with extensive rupture perpendicular to strike tend to have a longer initial wavelength than the recorded waveform, while sources with rupture primarily near the trench arrive too early at some of the DART buoys. Tsunami measurements in California, far from the Tohoku earthquake, can also be used to distinguish between sources based on waveform characteristics. In Crescent City, California, resonance in the harbor results in the first six waves being significant, allowing for the comparison of tsunami simulations to a long waveform. Most simulated tsunamis have similar wavelengths and general waveform to the recorded tide gauge observation, though they differ in the timing of the first arrival and the amplitude of the waves. Work to compare simulated tsunamis from multiple sources to tide gauges in other locations is ongoing.
Geomorphology of beach ridges and Holocene terraces on Kamchatka: A complex interplay of tectonics, volcanism and coastal processes
Despite decades of analysis, the origin of beach ridges remains debatable, and coastal morphotect... more Despite decades of analysis, the origin of beach ridges remains debatable, and coastal morphotectonics an open field. On the eastern coast of Kamchatka, along about 700 km of coastline (northwest Pacific and southwest Bering Sea), we have measured accumulative Holocene coastal profiles spanning a range of conditions including variable tectonics (co-seismic and longer term), wave climate, sea ice, and sediment
ABSTRACT A sand layer from a predecessor to the 2004 Indian Ocean tsunami underlies a freshwater ... more ABSTRACT A sand layer from a predecessor to the 2004 Indian Ocean tsunami underlies a freshwater marsh on Phra Thong Island, Phang Nga Province, Thailand. At this marsh, about 300 meters from the sea, the 2004 tsunami left a sand layer about 13 cm thick on top of a peaty soil. The previous tsunami deposit, of similar thickness, rests on another peaty soil about 40 cm below present ground surface. It probably correlates with a pre-2004 tsunami deposit previously reported from Phra Thong Island in a web posting by Shigehiro Fujino. Observed in trenches and cores, the pre-2004 deposit begins with a razor-sharp contact with the underlying soil. The sand itself contains no fewer than 6 layers, all horizontal, defined by differences in particle size (fine sand and very fine sand) and by detrital plant fragments. We also noticed pebble-size clasts of peaty soil. These observations come from the vicinity of UTM coordinates 418975E, 1009496N, zone 47. Many of us participated in previous, unsuccessful attempts to find pre-2004 tsunami deposits in Thailand. We hunted for sand sheets between Phuket to the south and Kho Khao Island to the north, on beach-ridge plains disturbed by tin mining and in mangrove swamps. We also checked pristine, grassy beach-ridge plains of Phra Thong Island, the next island north of Kho Khao. None of these environments offer both a host deposit that contrasts with tsunami-laid sand and a lack of disturbance by tin miners, mud lobsters, and real-estate developers.
Bourgeois, J.; Pinegina, T.; Martin, M. E.; Kravchunovskaya, E. American Geophysical Union, Fall ... more Bourgeois, J.; Pinegina, T.; Martin, M. E.; Kravchunovskaya, E. American Geophysical Union, Fall Meeting 2005, abstract #T11A-0360
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