Submarine landslides have been located along the central California continental margin with the u... more Submarine landslides have been located along the central California continental margin with the use of multibeam bathymetric and sub-bottom profiling data. These features are primarily concentrated on the lower continental slope and in submarine canyons. Recent evaluation of these landslides indicates that they are of various ages and types and formed in different ways. For example, the extensive slope failure morphology on the lower Point Sur slope range from subtle to very sharp geomorphic shapes that suggest these landslides have occurred over a long period of time. These landslides are large features (up to 215 km2) and form primarily from bottom-up processes in a retrogressive fashion. In contrast, some of the landslide scars located on flanks of submarine canyons appear youthful indicating recent activity. Several landslide scars and blocks are also located in the headward parts of Ascension and Monterey canyons. If these scars were generated by catastrophic slope failure, the...
In mountainous areas during intese rain events shallow landslides are often triggered adding thei... more In mountainous areas during intese rain events shallow landslides are often triggered adding their effect and enhancing the damaging consequences of flash flood. Many coastal area of the Mediterranean are exposed to such events, as recently largely happened in Italy, France, Spain and Greek. Large portions of the coastline mountainous territories have been settled and modified since ancient times with agricultural terraces, in order to practice the subsitence cultivation. This kind of anthropogenic modification of the slopes may be considered as an artificial immobilization of debris cover along steep slopes and, particularly after their abandonment, they can turn into sources of shallow landslides. Then terraces from belonging to soil and water conservation measures may represent a source of hazard if not properly mainteined. Considering the intense rain event that hit the Portofino promontory in 1915 causing strong damage to the Medieval monk Abbey in the iconic small San Fruttuoso village in northern Italy, a numerical modeling has been applied basing on historical testifying and the available evidences. A possible terraced area has been highlighted as a source area for the debris/mud flow that hit the Abbey and
Volcano lateral collapse landslides have produced a number of highly destructive tsunamis in hist... more Volcano lateral collapse landslides have produced a number of highly destructive tsunamis in historic time, and the largest such landslides may be the sources of extremely large or “mega-“ tsunamis. Amongst the historical examples of destructive tsunamis from volcano collapse landslides are Oshima Oshima 1741 in the Sea of Japan; Unzen 1792 in Kyushu, and Ritter Island 1888 in Papua New Guinea. The first and third of these are the largest such events, with volumes of about 2 km and 4 to 5 km respectively, for which we have eyewitness accounts of the resulting tsunami waves, but their volumes are only 0.1 – 1 % of the giant lateral collapses that occur at ocean island volcanoes over geological time. Nevertheless, they offer important “scale models” of the latter, as well as being representative of important hazard events at island arc and back arc volcanoes in their own right.
The tsunami generated by the 1995 Nuweiba Mw 7.2 earthquake in the Gulf of Elat-Aqaba (GOE) surpr... more The tsunami generated by the 1995 Nuweiba Mw 7.2 earthquake in the Gulf of Elat-Aqaba (GOE) surprised the local people who were not aware of seismogenic sea waves in their neighborhood, far away from the open sea. Furthermore, the tsunami was triggered by strike slip rupture along the main segment of the Dead Sea Transform system. Eyewitness reports and field observations that were collected after the event, as well as recorded mareogram, showed unequivocally that there was a tsunami and that tsunami hazard in the GOE needs focused examination. In order to investigate the event we adopted the GeoClaw package (LeVeque, 2006, Clawpack software) and simulated selected models of the 1995 Nuweiba earthquake. We then compared the calculated tsunami scenarios with the actual evidences and discuss the outcomes.
Most analyses of storm surge and inundation solve equations of continuity and momentum on fixed f... more Most analyses of storm surge and inundation solve equations of continuity and momentum on fixed finite-difference/finite-element meshes. I develop a completely new approach that uses a momentum equation to accelerate bits or balls of water over variable depth topography. The thickness of the water column at any point equals the volume density of balls there. In addition to being more intuitive than traditional methods, the tsunami ball approach has several advantages. (a) By tracking water balls of fixed volume, the continuity equation is satisfied automatically and the advection term in the momentum equation becomes unnecessary. (b) The procedure is meshless in the finite-difference/finite-element sense. (c) Tsunami balls care little if they find themselves in the ocean or inundating land. (d) Tsunami ball calculations of storm surge can be done on a laptop computer. I demonstrate and calibrate the method by simulating storm surge and inundation around New Orleans, Louisiana caused...
We support the revised estimate of tsunami source length (∼800 km) obtained by Neetu et al . Sea-... more We support the revised estimate of tsunami source length (∼800 km) obtained by Neetu et al . Sea-level monitoring with a high sampling rate, good azimuthal coverage, and real-time access, along with detailed bathymetry data around the stations, would improve source region estimation from tsunami arrival times.
This paper derives exact solutions to the equations of static plane strain by means of propagator... more This paper derives exact solutions to the equations of static plane strain by means of propagator matrices for homogeneous, gravitating and nongravitating elastic media. These solutions are immediately verifiable and are flexible under a variety of boundary conditions. Propagator matrices are eminently suitable for computer encoding and, through their multiplication, are applicable to depth-dependent structures. Attention is focused upon the bending of floating plates which are loaded to simulate the deflection of oceanic lithosphere in the vicinity of trenches. By comparing responses computed with and without body forces, I find that gravity does not meaningfully change deflection profiles; however, it can influence important aspects of the internal stress state. Gravitational stresses are proportional to the gradient of the vertical deformation and amount to about 10 per cent of the bending stresses in these models. Propagators which include gravity are used to investigate the effect of regional horizontal stresses upon bending plates. I conclude that applied compressive forces can transport the neutral surface through 10-20 km of depth without significantly deforming the plate profile or increasing the maximum internal stress by more than 30 per cent. These calculations support the contention that variable compressive stresses resulting from interplate coupling could account for observed regional differences in neutral surface height. For elastic-plastic material, the fundamental equations of motion become non-linear; however, there appears to be no a priori objection to their linearization. I speculate that the propagator formalism, when applied in an iterativeapproach, could be a powerful method for computing the deformation of such media.
Bulletin of the Seismological Society of America, 2004
This article simulates earthquake slip distributions as restricted random walks. Random walks off... more This article simulates earthquake slip distributions as restricted random walks. Random walks offer several unifying insights into earthquake behaviors that physically-based simulations do not. With properly tailored variables, random walks generate observed power law rates of earthquake number versus earthquake magnitude (the Gutenberg-Richter relation). Curiously b-value, the slope of this distribution, not only fixes the ratio of small to law events but it also dictates diverse earthquake scaling laws such as mean slip versus fault length and moment versus mean slip. Moreover, b-value determines the overall shape and roughness of earthquake ruptures. For example, mean random walk quakes with b=-1/2 have elliptical slip distributions characteristic of a uniform stress drop on a crack. Random walk earthquake simulators, tuned by comparison with field data, provide improved bases for statistical inference of earthquake behavior and hazard.
Propagator matrix solutions to the elastic equations of motion in spherically symmetric, inhomoge... more Propagator matrix solutions to the elastic equations of motion in spherically symmetric, inhomogeneous media with moment tensor sources are recast into a simple and intuitively satisfying form which is applicable to both exact and approximate calculations. The transformed expression benefits from the analogous equations of normal mode excitation, while clearly distinguishing the finer partitions of the displacement field and the more flexible boundary conditions that body wave formulations protide. I believe that this new representation, because of its many advantages, should be favoured as the foundation for elastic wave calculations in a sphere.
Very Long Baseline Interferometry (VLBI) determined site velocities from seven stations in wester... more Very Long Baseline Interferometry (VLBI) determined site velocities from seven stations in western Europe reveal a stable continental platform north of the Alps. Deformations between Sweden, Germany and Spain can not exceed 2 mm yr-'. South of the Alps, significant motions are occurring with respect to stable Europe. Two sites east of the Apennine mountains on peninsular Italy have north-easttrending velocities which increase from 2 mm yr-l in the north at Medicina to 6 mm yr-l in the south at Matera. In contrast, the VLBI site in the southeastern corner of Sicily is moving 7 mm yr-I to the north-northwest. These velocities are largely explained if southern Sicily is attached to a north-westerly moving African Plate and the eastern portion of the Italian peninsula forms part of a hypothesized Adriatic Sea crustal block which is rotating counterclockwise with respect to Europe about a pole near the Alps. Such an explanation is consistent with the styles of the larger historical earthquakes of the region, which show NE-SW extension across the Apennines, north-south convergence across the Alps, and NE-SW compression in coastal Yugoslavia. The Adria plate model generates 1.5-2.2 X 10l8 Nm yr-l of potential earthquake moment along the northern and central Apennines. Historical records suggest that 30-60 per cent of this moment is released seismically. Based on a direct-strain-rate measurement, recurrence intervals for Italian earthquakes south of Medicina are estimated to be 12-46 yr for M6.5+ quakes and 35-143 years for M7.0+ quakes.
Mma x the maximum magnitude arthquake that a fault is likely to suffer, plays an important role i... more Mma x the maximum magnitude arthquake that a fault is likely to suffer, plays an important role in earthquake hazard estimation. Although observational evidence summarized in plots of characteristic earthquake magnitude (Mch~) versus fault length indicate that smaller faults produce lower magnitude vents, an argument has been made that any fault regardless of its length should have Mm ~ near magnitude 8. The rationale for this argument charges that the contrary observational evidence stems from historical catalogs of limited extent and that it largely excludes noncon-ventional earthquakes in which several short and apparently disconnected fault seg-ments fail simultaneously. This article addresses Mma ~ using computer models of rupture on faults of various strengths and configurations. Computer models have advantages in that (a) Mr ~ earthquakes always can be generated by forcing complete stress drop on fully stressed faults, thus avoiding the limitations of short historical catalog...
Truth to say, for most of the three decades that we’ve been involved, tsunami research has been a... more Truth to say, for most of the three decades that we’ve been involved, tsunami research has been a fairly sleepy field. There happened the occasional tsunami in Japan or Central America and the odd Pacific warning issued for never-materialized waves [“tsu-NO-mi ” broadcast the next day’s headlines], but not much grabbed people’s attention for long. The past few years however have noticed a change of tide (sorry about that) in tsunami perceptions. Certainly this year’s events in the Indian Ocean forged the change, but the turn began earlier primarily due to massing information about “exotic ” tsunami sources like submarine landslides. With accelerating increases in sonar technologies, scientists began spotting undersea landslides everywhere — in submarine canyons, on continental slopes, adjacent to seamounts, and off the flanks of oceanic volcanoes. Like terrestrial slides, the submarine slides spanned a vast range of volume from <0.01 km 3 to>1000 km 3 [Figures 1, and 2]. With ...
Submarine landslides have been located along the central California continental margin with the u... more Submarine landslides have been located along the central California continental margin with the use of multibeam bathymetric and sub-bottom profiling data. These features are primarily concentrated on the lower continental slope and in submarine canyons. Recent evaluation of these landslides indicates that they are of various ages and types and formed in different ways. For example, the extensive slope failure morphology on the lower Point Sur slope range from subtle to very sharp geomorphic shapes that suggest these landslides have occurred over a long period of time. These landslides are large features (up to 215 km2) and form primarily from bottom-up processes in a retrogressive fashion. In contrast, some of the landslide scars located on flanks of submarine canyons appear youthful indicating recent activity. Several landslide scars and blocks are also located in the headward parts of Ascension and Monterey canyons. If these scars were generated by catastrophic slope failure, the...
In mountainous areas during intese rain events shallow landslides are often triggered adding thei... more In mountainous areas during intese rain events shallow landslides are often triggered adding their effect and enhancing the damaging consequences of flash flood. Many coastal area of the Mediterranean are exposed to such events, as recently largely happened in Italy, France, Spain and Greek. Large portions of the coastline mountainous territories have been settled and modified since ancient times with agricultural terraces, in order to practice the subsitence cultivation. This kind of anthropogenic modification of the slopes may be considered as an artificial immobilization of debris cover along steep slopes and, particularly after their abandonment, they can turn into sources of shallow landslides. Then terraces from belonging to soil and water conservation measures may represent a source of hazard if not properly mainteined. Considering the intense rain event that hit the Portofino promontory in 1915 causing strong damage to the Medieval monk Abbey in the iconic small San Fruttuoso village in northern Italy, a numerical modeling has been applied basing on historical testifying and the available evidences. A possible terraced area has been highlighted as a source area for the debris/mud flow that hit the Abbey and
Volcano lateral collapse landslides have produced a number of highly destructive tsunamis in hist... more Volcano lateral collapse landslides have produced a number of highly destructive tsunamis in historic time, and the largest such landslides may be the sources of extremely large or “mega-“ tsunamis. Amongst the historical examples of destructive tsunamis from volcano collapse landslides are Oshima Oshima 1741 in the Sea of Japan; Unzen 1792 in Kyushu, and Ritter Island 1888 in Papua New Guinea. The first and third of these are the largest such events, with volumes of about 2 km and 4 to 5 km respectively, for which we have eyewitness accounts of the resulting tsunami waves, but their volumes are only 0.1 – 1 % of the giant lateral collapses that occur at ocean island volcanoes over geological time. Nevertheless, they offer important “scale models” of the latter, as well as being representative of important hazard events at island arc and back arc volcanoes in their own right.
The tsunami generated by the 1995 Nuweiba Mw 7.2 earthquake in the Gulf of Elat-Aqaba (GOE) surpr... more The tsunami generated by the 1995 Nuweiba Mw 7.2 earthquake in the Gulf of Elat-Aqaba (GOE) surprised the local people who were not aware of seismogenic sea waves in their neighborhood, far away from the open sea. Furthermore, the tsunami was triggered by strike slip rupture along the main segment of the Dead Sea Transform system. Eyewitness reports and field observations that were collected after the event, as well as recorded mareogram, showed unequivocally that there was a tsunami and that tsunami hazard in the GOE needs focused examination. In order to investigate the event we adopted the GeoClaw package (LeVeque, 2006, Clawpack software) and simulated selected models of the 1995 Nuweiba earthquake. We then compared the calculated tsunami scenarios with the actual evidences and discuss the outcomes.
Most analyses of storm surge and inundation solve equations of continuity and momentum on fixed f... more Most analyses of storm surge and inundation solve equations of continuity and momentum on fixed finite-difference/finite-element meshes. I develop a completely new approach that uses a momentum equation to accelerate bits or balls of water over variable depth topography. The thickness of the water column at any point equals the volume density of balls there. In addition to being more intuitive than traditional methods, the tsunami ball approach has several advantages. (a) By tracking water balls of fixed volume, the continuity equation is satisfied automatically and the advection term in the momentum equation becomes unnecessary. (b) The procedure is meshless in the finite-difference/finite-element sense. (c) Tsunami balls care little if they find themselves in the ocean or inundating land. (d) Tsunami ball calculations of storm surge can be done on a laptop computer. I demonstrate and calibrate the method by simulating storm surge and inundation around New Orleans, Louisiana caused...
We support the revised estimate of tsunami source length (∼800 km) obtained by Neetu et al . Sea-... more We support the revised estimate of tsunami source length (∼800 km) obtained by Neetu et al . Sea-level monitoring with a high sampling rate, good azimuthal coverage, and real-time access, along with detailed bathymetry data around the stations, would improve source region estimation from tsunami arrival times.
This paper derives exact solutions to the equations of static plane strain by means of propagator... more This paper derives exact solutions to the equations of static plane strain by means of propagator matrices for homogeneous, gravitating and nongravitating elastic media. These solutions are immediately verifiable and are flexible under a variety of boundary conditions. Propagator matrices are eminently suitable for computer encoding and, through their multiplication, are applicable to depth-dependent structures. Attention is focused upon the bending of floating plates which are loaded to simulate the deflection of oceanic lithosphere in the vicinity of trenches. By comparing responses computed with and without body forces, I find that gravity does not meaningfully change deflection profiles; however, it can influence important aspects of the internal stress state. Gravitational stresses are proportional to the gradient of the vertical deformation and amount to about 10 per cent of the bending stresses in these models. Propagators which include gravity are used to investigate the effect of regional horizontal stresses upon bending plates. I conclude that applied compressive forces can transport the neutral surface through 10-20 km of depth without significantly deforming the plate profile or increasing the maximum internal stress by more than 30 per cent. These calculations support the contention that variable compressive stresses resulting from interplate coupling could account for observed regional differences in neutral surface height. For elastic-plastic material, the fundamental equations of motion become non-linear; however, there appears to be no a priori objection to their linearization. I speculate that the propagator formalism, when applied in an iterativeapproach, could be a powerful method for computing the deformation of such media.
Bulletin of the Seismological Society of America, 2004
This article simulates earthquake slip distributions as restricted random walks. Random walks off... more This article simulates earthquake slip distributions as restricted random walks. Random walks offer several unifying insights into earthquake behaviors that physically-based simulations do not. With properly tailored variables, random walks generate observed power law rates of earthquake number versus earthquake magnitude (the Gutenberg-Richter relation). Curiously b-value, the slope of this distribution, not only fixes the ratio of small to law events but it also dictates diverse earthquake scaling laws such as mean slip versus fault length and moment versus mean slip. Moreover, b-value determines the overall shape and roughness of earthquake ruptures. For example, mean random walk quakes with b=-1/2 have elliptical slip distributions characteristic of a uniform stress drop on a crack. Random walk earthquake simulators, tuned by comparison with field data, provide improved bases for statistical inference of earthquake behavior and hazard.
Propagator matrix solutions to the elastic equations of motion in spherically symmetric, inhomoge... more Propagator matrix solutions to the elastic equations of motion in spherically symmetric, inhomogeneous media with moment tensor sources are recast into a simple and intuitively satisfying form which is applicable to both exact and approximate calculations. The transformed expression benefits from the analogous equations of normal mode excitation, while clearly distinguishing the finer partitions of the displacement field and the more flexible boundary conditions that body wave formulations protide. I believe that this new representation, because of its many advantages, should be favoured as the foundation for elastic wave calculations in a sphere.
Very Long Baseline Interferometry (VLBI) determined site velocities from seven stations in wester... more Very Long Baseline Interferometry (VLBI) determined site velocities from seven stations in western Europe reveal a stable continental platform north of the Alps. Deformations between Sweden, Germany and Spain can not exceed 2 mm yr-'. South of the Alps, significant motions are occurring with respect to stable Europe. Two sites east of the Apennine mountains on peninsular Italy have north-easttrending velocities which increase from 2 mm yr-l in the north at Medicina to 6 mm yr-l in the south at Matera. In contrast, the VLBI site in the southeastern corner of Sicily is moving 7 mm yr-I to the north-northwest. These velocities are largely explained if southern Sicily is attached to a north-westerly moving African Plate and the eastern portion of the Italian peninsula forms part of a hypothesized Adriatic Sea crustal block which is rotating counterclockwise with respect to Europe about a pole near the Alps. Such an explanation is consistent with the styles of the larger historical earthquakes of the region, which show NE-SW extension across the Apennines, north-south convergence across the Alps, and NE-SW compression in coastal Yugoslavia. The Adria plate model generates 1.5-2.2 X 10l8 Nm yr-l of potential earthquake moment along the northern and central Apennines. Historical records suggest that 30-60 per cent of this moment is released seismically. Based on a direct-strain-rate measurement, recurrence intervals for Italian earthquakes south of Medicina are estimated to be 12-46 yr for M6.5+ quakes and 35-143 years for M7.0+ quakes.
Mma x the maximum magnitude arthquake that a fault is likely to suffer, plays an important role i... more Mma x the maximum magnitude arthquake that a fault is likely to suffer, plays an important role in earthquake hazard estimation. Although observational evidence summarized in plots of characteristic earthquake magnitude (Mch~) versus fault length indicate that smaller faults produce lower magnitude vents, an argument has been made that any fault regardless of its length should have Mm ~ near magnitude 8. The rationale for this argument charges that the contrary observational evidence stems from historical catalogs of limited extent and that it largely excludes noncon-ventional earthquakes in which several short and apparently disconnected fault seg-ments fail simultaneously. This article addresses Mma ~ using computer models of rupture on faults of various strengths and configurations. Computer models have advantages in that (a) Mr ~ earthquakes always can be generated by forcing complete stress drop on fully stressed faults, thus avoiding the limitations of short historical catalog...
Truth to say, for most of the three decades that we’ve been involved, tsunami research has been a... more Truth to say, for most of the three decades that we’ve been involved, tsunami research has been a fairly sleepy field. There happened the occasional tsunami in Japan or Central America and the odd Pacific warning issued for never-materialized waves [“tsu-NO-mi ” broadcast the next day’s headlines], but not much grabbed people’s attention for long. The past few years however have noticed a change of tide (sorry about that) in tsunami perceptions. Certainly this year’s events in the Indian Ocean forged the change, but the turn began earlier primarily due to massing information about “exotic ” tsunami sources like submarine landslides. With accelerating increases in sonar technologies, scientists began spotting undersea landslides everywhere — in submarine canyons, on continental slopes, adjacent to seamounts, and off the flanks of oceanic volcanoes. Like terrestrial slides, the submarine slides spanned a vast range of volume from <0.01 km 3 to>1000 km 3 [Figures 1, and 2]. With ...
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Papers by Steven Ward