Showing papers in "Pure and Applied Geophysics in 2015"

Seismic Tomography of the Southern California Plate Boundary Region from Noise-Based Rayleigh and Love Waves

Abstract: We use cross-correlations of ambient seismic noise between pairs of 158 broadband and short-period sensors to investigate velocity structure over the top 5–10 km of the crust in the Southern California plate boundary region around the San Jacinto Fault Zone (SJFZ). From the 9-component correlation tensors associated with all station pairs we derive dispersion curves of Rayleigh and Love wave group velocities. The dispersion results are inverted first for Rayleigh and Love waves group velocity maps on a 1.5 × 1.5 km2 grid that includes portions of the SJFZ, the San Andreas Fault (SAF), and the Elsinore fault. We then invert these maps to 3D shear wave velocities in the top ~7 km of the crust. The distributions of the Rayleigh and Love group velocities exhibit 2θ azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas. The reconstructed 3D shear velocity model reveals complex shallow structures correlated with the main geological units, and strong velocity contrasts across various fault sections along with low-velocity damage zones and basins. The SJFZ is marked by a clear velocity contrast with higher V s values on the NE block for the section SE of the San Jacinto basin and a reversed contrast across the section between the San Jacinto basin and the SAF. Velocity contrasts are also observed along the southern parts on the SAF and the Elsinore fault, with a faster southwest block in both cases. The region around the Salton Trough is associated with a significant low-velocity zone. Strong velocity reductions following flower-shape with depth are observed extensively around both the SJFZ and the SAF, and are especially prominent in areas of geometrical complexity. In particular, the area between the SJFZ and the SAF is associated with an extensive low-velocity zone correlated with diffuse seismicity at depth, and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the SJFZ. These results augment local earthquake tomography images that have low resolution in the top few km of the crust, and provide important constraints for studies concerned with behavior of earthquake ruptures, generation of rock damage, and seismic shaking hazard in the region.

Parallel Implementation of Dispersive Tsunami Wave Modeling with a Nesting Algorithm for the 2011 Tohoku Tsunami

Abstract: Because of improvements in offshore tsunami observation technology, dispersion phenomena during tsunami propagation have often been observed in recent tsunamis, for example the 2004 Indian Ocean and 2011 Tohoku tsunamis. The dispersive propagation of tsunamis can be simulated by use of the Boussinesq model, but the model demands many computational resources. However, rapid progress has been made in parallel computing technology. In this study, we investigated a parallelized approach for dispersive tsunami wave modeling. Our new parallel software solves the nonlinear Boussinesq dispersive equations in spherical coordinates. A variable nested algorithm was used to increase spatial resolution in the target region. The software can also be used to predict tsunami inundation on land. We used the dispersive tsunami model to simulate the 2011 Tohoku earthquake on the Supercomputer K. Good agreement was apparent between the dispersive wave model results and the tsunami waveforms observed offshore. The finest bathymetric grid interval was 2/9 arcsec (approx. 5 m) along longitude and latitude lines. Use of this grid simulated tsunami soliton fission near the Sendai coast. Incorporating the three-dimensional shape of buildings and structures led to improved modeling of tsunami inundation.

A 21-Event, 4,000-Year History of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term Earthquake Production on a Major Plate Boundary Fault

Abstract: Paleoseismic work completed at Hog Lake on the San Jacinto Fault (SJF) near Anza, California, indicates that at least 21 surface ruptures have occurred in the Anza Seismic gap over the past 4,000 years. The ages of the ruptures are constrained by 111 radiocarbon dates, 97 of which fall in stratigraphic order. The average recurrence interval for all ruptures for this period is about 185 ± 105 years, although some ruptures, such as occurred in the April 1918 earthquake, caused only minor displacement. We rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo-ground surface. Weakly expressed ruptures, for example the deformation we interpret to be the result of the historical 1918 earthquake, received low scores and are interpreted as smaller earthquakes. From this analysis, we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake, inferred to be the M w 7.3 22 November 1800 earthquake. The adjusted recurrence interval for large earthquakes lengthens to approximately 254 years. Comparison with the rupture history at the Mystic Lake paleoseismic site on the Claremont strand indicates that it is plausible that several of the large ruptures identified at Hog Lake could have jumped the Hemet step-over at Mystic Lake and continued on the Claremont strand (or vice versa), but most of the event ages do not match between the two sites, indicating that most ruptures do not jump the step. Finally, comparison with San Andreas Fault ruptures both to the north and south of its juncture with the SJF suggest that some northern SJF ruptures identified at Mystic Lake may correlate with events identified at Wrightwood, but that these northern ruptures have no match at Hog Lake and can not indicate rupture of the entire SJF onto the SAF.

Deep-Ocean Measurements of Tsunami Waves

Abstract: Deep-ocean tsunami measurements play a major role in understanding the physics of tsunami wave generation and propagation, and in improving the effectiveness of tsunami warning systems This paper provides an overview of the history of tsunami recording in the open ocean from the earliest days, approximately 50 years ago, to the present day Modern tsunami monitoring systems such as the self-contained Deep-ocean Assessment and Reporting of Tsunamis and innovative cabled sensing networks, including, but not limited to, the Japanese bottom cable projects and the NEPTUNE-Canada geophysical bottom observatory, are highlighted The specific peculiarities of seafloor longwave observations in the deep ocean are discussed and compared with observations recorded in coastal regions Tsunami detection in bottom pressure observations is exemplified through analysis of distant (22,000 km from the source) records of the 2004 Sumatra tsunami in the northeastern Pacific

A Decade After the 2004 Indian Ocean Tsunami: The Progress in Disaster Preparedness and Future Challenges in Indonesia, Sri Lanka, Thailand and the Maldives

Abstract: The 2004 Indian Ocean tsunami was one of the most devastating tsunamis in world history. The tsunami caused damage to most of the Asian and other countries bordering the Indian Ocean. After a decade, reconstruction has been completed with different levels of tsunami countermeasures in most areas; however, some land use planning using probabilistic tsunami hazard maps and vulnerabilities should be addressed to prepare for future tsunamis. Examples of early-stage reconstruction are herein provided alongside a summary of some of the major tsunamis that have occurred since 2004, revealing the tsunami countermeasures established during the reconstruction period. Our primary objective is to report on and discuss the vulnerabilities found during our field visits to the tsunami-affected countries—namely, Indonesia, Sri Lanka, Thailand and the Maldives. For each country, future challenges based on current tsunami countermeasures, such as land use planning, warning systems, evacuation facilities, disaster education and disaster monuments are explained. The problem of traffic jams during tsunami evacuations, especially in well-known tourist areas, was found to be the most common problem faced by all of the countries. The readiness of tsunami warning systems differed across the countries studied. These systems are generally sufficient on a national level, but local hazards require greater study. Disaster reduction education that would help to maintain high tsunami awareness is well established in most countries. Some geological evidence is well preserved even after a decade. Conversely, the maintenance of monuments to the 2004 tsunami appears to be a serious problem. Finally, the reconstruction progress was evaluated based on the experiences of disaster reconstruction in Japan. All vulnerabilities discussed here should be addressed to create long-term, disaster-resilient communities.

The seismotectonics of the Po Plain (northern Italy): tectonic diversity in a blind faulting domain

Abstract: We present a systematic and updated overview of a seismotectonic model for the Po Plain (northern Italy). This flat and apparently quiet tectonic domain is, in fact, rather active as it comprises the shortened foreland and foredeep of both the Southern Alps and the Northern Apennines. Assessing its seismic hazard is crucial due to the concentration of population, industrial activities, and critical infrastructures, but it is also complicated because (a) the region is geologically very diverse, and (b) nearly all potential seismogenic faults are buried beneath a thick blanket of Pliocene–Pleistocene sediments, and thus can be investigated only indirectly. Identifying and parameterizing the potential seismogenic faults of the Po Plain requires proper consideration of their depth, geometry, kinematics, earthquake potential and location with respect to the two confronting orogens. To this end, we subdivided them into four main, homogeneous groups. Over the past 15 years we developed new strategies for coping with this diversity, resorting to different data and modeling approaches as required by each individual fault group. The most significant faults occur beneath the thrust fronts of the Ferrara-Romagna and Emilia arcs, which correspond to the most advanced and buried portions of the Northern Apennines and were the locus of the destructive May 2012 earthquake sequence. The largest known Po Plain earthquake, however, occurred on an elusive reactivated fault cutting the Alpine foreland south of Verona. Significant earthquakes are expected to be generated also by a set of transverse structures segmenting the thrust system, and by the deeper ramps of the Apennines thrusts. The new dataset is intended to be included in the next version of the Database of Individual Seismogenic Sources (DISS; http://diss.rm.ingv.it/diss/ , version 3.2.0, developed and maintained by INGV) to improve completeness of potential sources for seismic hazard assessment.

Recent Advances in Agent-Based Tsunami Evacuation Simulations: Case Studies in Indonesia, Thailand, Japan and Peru

Abstract: As confirmed by the extreme tsunami events over the last decade (the 2004 Indian Ocean, 2010 Chile and 2011 Japan tsunami events), mitigation measures and effective evacuation planning are needed to reduce disaster risks. Modeling tsunami evacuations is an alternative means to analyze evacuation plans and possible scenarios of evacuees’ behaviors. In this paper, practical applications of an agent-based tsunami evacuation model are presented to demonstrate the contributions that agent-based modeling has added to tsunami evacuation simulations and tsunami mitigation efforts. A brief review of previous agent-based evacuation models in the literature is given to highlight recent progress in agent-based methods. Finally, challenges are noted for bridging gaps between geoscience and social science within the agent-based approach for modeling tsunami evacuations.

New Insights into the Source of the Makran Tsunami of 27 November 1945 from Tsunami Waveforms and Coastal Deformation Data

Abstract: We constrain the source of the 27 November 1945 tsunami in the Makran Subduction Zone (MSZ) using available tsunami waveforms recorded on tide gauges at Mumbai (India) and Karachi (Pakistan), and that inferred at Port Victoria (Seychelles), and coseismic deformation data along the Makran coast. Spectral analysis of the tsunami waveforms shows that the tsunami governing period was 40–50 min at Karachi whereas it was around 22 min at Mumbai. The inferred tsunami waveform at Port Victoria also indicated a period of around 21 min for the tsunami. Tsunami numerical simulations from the previously proposed source models failed in reproducing the observed tsunami waveforms and coseismic deformation data. Sensitivity analysis showed that the source fault needs to be extended offshore into deep water in order to reproduce the first 22-min signal at Mumbai. Based on the inversion of the observed tsunami waveforms, we propose a four-segment fault with varying slip amounts as the final source. This source includes a slip of 4.3 m onshore near Ormara (Pakistan) and a slip of 10 m offshore at water depth of around 3,000 m. The total fault length is 220 km, and the average slip is 6.1 m. This source, first, reproduces fairly well the observed tide gauge records at Mumbai and Karachi, second, produces ~1 m of uplift at Ormara and ~1 m of subsidence at Pasni, and third, gives a moment magnitude of 8.3 for the earthquake, which is in the acceptable range of seismic data. The computed 1 m uplift at Ormara is in the uplift range of 1–3 m reported in the literature. As the tide gauge stations were located in the far field, our proposed source explains mainly the tectonic source of the tsunami.

Dynamic Ruptures on a Frictional Interface with Off-Fault Brittle Damage: Feedback Mechanisms and Effects on Slip and Near-Fault Motion

Abstract: The spontaneous generation of brittle rock damage near and behind the tip of a propagating rupture can produce dynamic feedback mechanisms that modify significantly the rupture properties, seismic radiation, and generated fault zone structure. In this work, we study such feedback mechanisms for single rupture events and their consequences for earthquake physics and various possible observations. This is done through numerical simulations of in-plane dynamic ruptures on a frictional fault with bulk behavior governed by a brittle damage rheology that incorporates reduction of elastic moduli in off-fault yielding regions. The model simulations produce several features that modify key properties of the ruptures, local wave propagation, and fault zone damage. These include (1) dynamic generation of near-fault regions with lower elastic properties, (2) dynamic changes of normal stress on the fault, (3) rupture transition from crack-like to a detached pulse, (4) emergence of a rupture mode consisting of a train of pulses, (5) quasi-periodic modulation of slip rate on the fault, and (6) asymmetric near-fault ground motion with higher amplitude and longer duration on the side with reduced elastic moduli. The results can have significant implications to multiple topics ranging from rupture directivity and local amplification of seismic motion to near-fault tremor-like signals.

Multi-Temporal Evaluation of Landslide Movements and Impacts on Buildings in San Fratello (Italy) By Means of C-Band and X-Band PSI Data

Abstract: This work provides a multi-temporal and spatial investigation of landslide effects in the San Fratello area (Messina province within the Sicily region, Italy), by means of C-band and X-band Persistent Scatterer Interferometry (PSI) data, integrated with in situ field checks and a crack pattern survey. The Sicily region is extensively affected by hydrogeological hazards since several landslides regularly involved local areas across time. In particular, intense and catastrophic landslide phenomena have recently occurred in the San Fratello area; the last event took place in February 2010, causing large economic damage. Thus, the need for an accurate ground motions and impacts mapping and monitoring turns out to be significantly effective, in order to better identify active unstable areas and to help proper risk-mitigation measures planning. The combined use of historical and recent C-band satellites and current X-band Synthetic Aperture Radar sensors of a new generation permits spatially and temporally detection of landslide-induced motions on a local scale and to properly provide a complete multi-temporal evaluation of their effects on the area of interest. PSI ground motion rates are cross-compared with local failures and damage of involved buildings, recently recognized by in situ observations. As a result, the analysis of landslide-induced movements over almost 20 years and the validation of radar data with manufactured crack patterns, permits one to finally achieve a complete and reliable assessment in the San Fratello test site.

Tsunami Squares Approach to Landslide-Generated Waves: Application to Gongjiafang Landslide, Three Gorges Reservoir, China

Abstract: We have developed a new method, named “Tsunami Squares”, for modeling of landslides and landslide-generated waves. The approach has the advantages of the previous “Tsunami Ball” method, for example, separate, special treatment for dry and wet cells is not needed, but obviates the use of millions of individual particles. Simulations now can be expanded to spatial scales not previously possible. The new method accelerates and transports “squares” of material that are fractured into new squares in such a way as to conserve volume and linear momentum. The simulation first generates landslide motion as constrained by direct observation. It then computes induced water waves, given assumptions about energy and momentum transfer. We demonstrated and validated the Tsunami Squares method by modeling the 2008 Three Gorges Reservoir Gongjiafang landslide and river tsunami. The landslide’s progressive failure, the wave generated, and its subsequent propagation and run-up are well reproduced. On a laptop computer Tsunami Square simulations flexibly handle a wide variety of waves and flows, and are excellent techniques for risk estimation.

A User-Oriented Methodology for DInSAR Time Series Analysis and Interpretation: Landslides and Subsidence Case Studies

Abstract: Recent advances in multi-temporal Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) have greatly improved our capability to monitor geological processes. Ground motion studies using DInSAR require both the availability of good quality input data and rigorous approaches to exploit the retrieved Time Series (TS) at their full potential. In this work we present a methodology for DInSAR TS analysis, with particular focus on landslides and subsidence phenomena. The proposed methodology consists of three main steps: (1) pre-processing, i.e., assessment of a SAR Dataset Quality Index (SDQI) (2) post-processing, i.e., application of empirical/stochastic methods to improve the TS quality, and (3) trend analysis, i.e., comparative implementation of methodologies for automatic TS analysis. Tests were carried out on TS datasets retrieved from processing of SAR imagery acquired by different radar sensors (i.e., ERS-1/2 SAR, RADARSAT-1, ENVISAT ASAR, ALOS PALSAR, TerraSAR-X, COSMO-SkyMed) using advanced DInSAR techniques (i.e., SqueeSAR™, PSInSAR™, SPN and SBAS). The obtained values of SDQI are discussed against the technical parameters of each data stack (e.g., radar band, number of SAR scenes, temporal coverage, revisiting time), the retrieved coverage of the DInSAR results, and the constraints related to the characterization of the investigated geological processes. Empirical and stochastic approaches were used to demonstrate how the quality of the TS can be improved after the SAR processing, and examples are discussed to mitigate phase unwrapping errors, and remove regional trends, noise and anomalies. Performance assessment of recently developed methods of trend analysis (i.e., PS-Time, Deviation Index and velocity TS) was conducted on two selected study areas in Northern Italy affected by land subsidence and landslides. Results show that the automatic detection of motion trends enhances the interpretation of DInSAR data, since it provides an objective picture of the deformation behaviour recorded through TS and therefore contributes to the understanding of the on-going geological processes.

A New Method for Depth and Shape Determinations from Magnetic Data

Abstract: We present in this paper a new formula representing the magnetic anomaly expressions produced by most geological structures. Using the new formula we developed a simple and fast numerical method to determine simultaneously the depth and shape of a buried structure from second-horizontal derivative anomalies obtained from magnetic data with filters of successive window lengths. The method involves using a nonlinear relationship between the depth to the source and the shape factor and a combination of observations at four points with respect to the coordinate of the source center with a free parameter (window length). The relationship represents a parametric family of curves (window curves). For a fixed free parameter, the depth is determined for each shape factor. The computed depths are plotted against the shape factors representing a continuous monotonically increasing curve. The solution for the shape and depth of the buried structure is read at the common intersection of the window curves. This method can be applied to residuals as well as to the observed magnetic data consisting of the combined effect of a local structure and a second-order regional or less. The method is applied to synthetic data with and without random errors and tested on three field examples from India, Brazil and the USA. In all cases the shape and depth of the buried structures are in good agreement with the actual ones.

Far-Field Tsunami Impact in the North Atlantic Basin from Large Scale Flank Collapses of the Cumbre Vieja Volcano, La Palma

Abstract: In their pioneering work, Ward and Day suggested that a large scale flank collapse of the Cumbre Vieja Volcano (CVV) on La Palma (Canary Islands) could trigger a mega-tsunami throughout the North Atlantic Ocean basin, causing major coastal impact in the far-field. While more recent studies indicate that near-field waves from such a collapse would be more moderate than originally predicted by Ward and Day [Lovholt et al. (J Geophy Res 113:C09026, 2008); Abadie et al. (J Geophy Res 117:C05030, 2012)], these would still be formidable and devastate the Canary Island, while causing major impact in the far-field at many locations along the western European, African, and the US east coasts. Abadie et al. (J Geophy Res 117:C05030, 2012) simulated tsunami generation and near-field tsunami impact from a few CVV subaerial slide scenarios, with volumes ranging from 20 to 450 km $$^3$$ ; the latter representing the most extreme scenario proposed by Ward and Day. They modeled tsunami generation, i.e., the tsunami source, using THETIS, a 3D Navier-Stokes (NS) multi-fluid VOF model, in which slide material was considered as a nearly inviscid heavy fluid. Near-field tsunami impact was then simulated for each source using FUNWAVE-TVD, a dispersive and fully nonlinear long wave Boussinesq model [Shi et al. (Ocean Modell 43–44:36–51, 2012); Kirby et al. (Ocean Modeling, 62:39–55, 2013)]. Here, using FUNWAVE-TVD for a series of nested grids of increasingly fine resolution, we model and analyze far-field tsunami impact from two of Abadie et al.’s extreme CVV flank collapse scenarios: (i) that deemed the most “credible worst case scenario” based on a slope stability analysis, with a 80 km $$^3$$ volume; and (ii) the most extreme scenario, similar to Ward and Day’s, with a 450 km $$^3$$ volume. Simulations are performed using a one-way coupling scheme in between two given levels of nested grids. Based on the simulation results, the overall tsunami impact is first assessed in terms of maximum surface elevation computed along the western European and African, and US east coasts (USEC). Strong wave elevation decay is predicted over the wide USEC shelf, which is shown to be essentially due to bottom friction effects. We then show more detailed results for the USEC, which is the object of high-resolution tsunami inundation mapping under the auspices of the US National Tsunami Hazard Mitigation Program. In this context, we compare the maximum surface elevation predicted along the coastline for each CVV scenario and show that, besides the initial directionality of the sources, coastal impact is mostly controlled by focusing/defocusing effects resulting from the shelf bathymetric features. A simplified ray-tracing analysis confirms this controlling effect of the wide USEC shelf for incident long waves. Finally, we perform high-resolution (10 m) inundation mapping for the most extreme CVV scenario and show results at one of the most vulnerable and exposed communities in the mid-Atlantic US states, in and around Ocean City, Maryland. Such maps are being generated for all exposed areas of the USEC, to be used in tsunami hazard assessment and mitigation work.

Fault Geometry and Active Stress from Earthquakes and Field Geology Data Analysis: The Colfiorito 1997 and L’Aquila 2009 Cases (Central Italy)

Abstract: The fault segmentation pattern and the regional stress tensor acting since the Early Quaternary in the intra-Apennine area of central Italy was constrained by integrating two large geological and seismological fault-slip data sets collected for the areas struck by the two most energetic seismic sequences of the last 15 years (Colfiorito 1997, M w 6.0 and L’Aquila 2009, M w 6.1). The integrated analysis of the earthquake fault association and the reconstruction of the 3D shape of the seismogenic sources were exploited to identify homogeneous seismogenic volumes associated with subsets of geological and focal mechanism data. The independent analysis of geological and seismological data allowed us to observe and highlight similarities between the attitude of the long-term (e.g., Quaternary) and the instantaneous present-day (seismogenic) extensional deformations and to reveal their substantial coaxiality. Coherently, with the results from the kinematic analysis, the stress field inversion also noted a prevailing tensional seismotectonic regime associated with a subhorizontal, NE–SW, minimum stress axis. A minor, very local, and shallow (<5 km) strike-slip component of the stress field was observed in the Colfiorito sector, where an inherited N–S oriented right-lateral fault was reactivated with sinistral kinematics. Instead, an almost total absence of strike-slip solutions was observed in the L’Aquila area. These results do not agree with those indicating Quaternary regional strike-slip regimes or wide areas characterized by strike-slip deformation during the Colfiorito and L’Aquila seismic sequences.

Postseismic Deformation Following the 2010 M = 7.2 El Mayor-Cucapah Earthquake: Observations, Kinematic Inversions, and Dynamic Models

Abstract: Due to its location on a transtensional section of the Pacific-North American plate boundary, the Salton Trough is a region featuring large strike-slip earthquakes within a regime of shallow asthenosphere, high heat flow, and complex faulting, and so postseismic deformation there may feature enhanced viscoelastic relaxation and afterslip that is particularly detectable at the surface The 2010 M=72 El Mayor-Cucapah earthquake was the largest shock in the Salton Trough since 1892 and occurred close to the US-Mexico border, and so the postseismic deformation recorded by the continuous GPS network of southern California provides an opportunity to study the rheology of this region Three-year postseismic transients extracted from GPS displacement time-series show four key features: (1) 1–2 cm of cumulative uplift in the Imperial Valley and ∼ 1 cm of subsidence in the Peninsular Ranges, (2) relatively large cumulative horizontal displacements > 150 km from the rupture in the Peninsular Ranges, (3) rapidly decaying horizontal displacement rates in the first few months after the earthquake in the Imperial Valley, and (4) sustained horizontal velocities, following the rapid early motions, that were still visibly ongoing 3 years after the earthquake Kinematic inversions show that the cumulative 3-year postseismic displacement field can be well fit by afterslip on and below the coseismic rupture, though these solutions require afterslip with a total moment equivalent to at least a M=72 earthquake and higher slip magnitudes than those predicted by coseismic stress changes Forward modeling shows that stress-driven afterslip and viscoelastic relaxation in various configurations within the lithosphere can reproduce the early and later horizontal velocities in the Imperial Valley, while Newtonian viscoelastic relaxation in the asthenosphere can reproduce the uplift in the Imperial Valley and the subsidence and large westward displacements in the Peninsular Ranges We present two forward models of dynamically coupled deformation mechanisms that fit the postseismic transient well: a model combining afterslip in the lower crust, Newtonian viscoelastic relaxation in a localized zone in the lower crust beneath areas of high heat flow and geothermal activity, and Newtonian viscoelastic relaxation in the asthenosphere; and a second model that replaces the afterslip in the first model with viscoelastic relaxation with a stress-dependent viscosity in the mantle The rheology of this high-heat-flow, high-strain-rate region may incorporate elements of both these models and may well be more complex than either of them

Performance Benchmarking Tsunami Models for NTHMP’s Inundation Mapping Activities

Abstract: The coastal states and territories of the United States (US) are vulnerable to devastating tsunamis from near-field or far-field coseismic and underwater/subaerial landslide sources. Following the catastrophic 2004 Indian Ocean tsunami, the National Tsunami Hazard Mitigation Program (NTHMP) accelerated the development of public safety products for the mitigation of these hazards. In response to this initiative, US coastal states and territories speeded up the process of developing/enhancing/adopting tsunami models that can be used for developing inundation maps and evacuation plans. One of NTHMP’s requirements is that all operational and inundation-based numerical (OI since they are considered as sufficiently comprehensive. Average relative errors associated with expected parameters values such as maximum surface amplitude/runup are estimated. The level of agreement with the reference data, reasons for discrepancies between model results, and some of the limitations are discussed. In general, dispersive models were found to perform better than nondispersive models, but differences were relatively small, in part because the BPs mostly featured long waves, such as solitary waves. The largest error found (e.g., the laboratory experiment case of a solitary wave on a simple beach) was 10 % for non-breaking wave conditions and 12 % for breaking conditions; these errors are equal or smaller than the thresholds (10 % and 20 %, respectively) defined by the OAR-PMEL-135 for predicting the surface profile; hence, all models examined here are deemed acceptable for inundation mapping purposes.

Effect of Upper Mantle Density Structure on Moho Geometry

Abstract: A constant value of the Moho density contrast is often assumed in the gravimetric methods used for determination of Moho geometry. This assumption might be sufficient in regional studies with a relatively homogenous lithospheric structure (and, consequently, small lateral variations in Moho density contrast). In global studies, however, this assumption is not reasonable, because not only the Moho depth but also the Moho density contrast vary substantially, and are, thus, likely to result in systematic errors in Moho geometry determined globally from gravity data. In this study we address this issue by investigating the effect of variable Moho density contrast on Moho geometry. We demonstrate that assumption of variable Moho density contrast (instead of a uniform model) substantially improves agreement between the global gravimetric and seismic Moho models by approximately 30 %.

Probabilistic Tsunami Hazard in the Northeast Atlantic from Near- and Far-Field Tectonic Sources

Abstract: In this article, we present the first study on probabilistic tsunami hazard assessment for the Northeast (NE) Atlantic region related to earthquake sources. The methodology combines the probabilistic seismic hazard assessment, tsunami numerical modeling, and statistical approaches. We consider three main tsunamigenic areas, namely the Southwest Iberian Margin, the Gloria, and the Caribbean. For each tsunamigenic zone, we derive the annual recurrence rate for each magnitude range, from Mw 8.0 up to Mw 9.0, with a regular interval, using the Bayesian method, which incorporates seismic information from historical and instrumental catalogs. A numerical code, solving the shallow water equations, is employed to simulate the tsunami propagation and compute near shore wave heights. The probability of exceeding a specific tsunami hazard level during a given time period is calculated using the Poisson distribution. The results are presented in terms of the probability of exceedance of a given tsunami amplitude for 100- and 500-year return periods. The hazard level varies along the NE Atlantic coast, being maximum along the northern segment of the Morocco Atlantic coast, the southern Portuguese coast, and the Spanish coast of the Gulf of Cadiz. We find that the probability that a maximum wave height exceeds 1 m somewhere in the NE Atlantic region reaches 60 and 100 % for 100- and 500-year return periods, respectively. These probability values decrease, respectively, to about 15 and 50 % when considering the exceedance threshold of 5 m for the same return periods of 100 and 500 years.

Validating Velocities in the GeoClaw Tsunami Model Using Observations near Hawaii from the 2011 Tohoku Tsunami

Abstract: 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 waveform or height and, therefore, may be a more sensitive variable for model validation.

Progress on Development of an Earthquake Early Warning System Using Low-Cost Sensors

Abstract: Taiwan is one of the leading developers of earthquake early warning (EEW) systems The Central Weather Bureau has been the primary developer of the EEW system in Taiwan since 1993 In 2010, the National Taiwan University (NTU) developed an EEW system for research purposes using low-cost accelerometers As of 2014, a total of 506 stations have been deployed and configured The NTU system can provide earthquake information within 15 s of an earthquake occurrence Thus, this system may provide early warnings for cities located more than 50 km from the epicenter Additionally, the NTU system also has an onsite alert function that triggers a warning for incoming P-waves greater than a certain magnitude threshold, thus providing a 2–3 s lead time before peak ground acceleration for regions close to an epicenter Detailed shaking maps are produced by the NTU system within one or two minutes after an earthquake Regions of high shaking indicated by the shalking map can indicate locations of damage and casualties and help estimate the damage incurred The direction of earthquake ruptures are also potentially identified based on detailed shaking maps and strong motion records of the NTU system

Application of Short-Offset TEM (SOTEM) Technique in Mapping Water-Enriched Zones of Coal Stratum, an Example from East China

Abstract: Water inrush from limestone coal beds is disastrous for coal mining. In general, it is very difficult to detect such water-enriched zones because of their relatively large burial depth. In this paper, we propose a novel transient electromagnetic method (TEM) configuration, short-offset transient electromagnetic method (SOTEM). Consistency of the results obtained from SOTEM measurements in the Shandong province, East China and drilling information indicate that the proposed TEM configuration not only improves the accuracy, but also enlarges the exploration depth for detecting water-enriched areas in coal mines ranging from 1,000 to 1,200 m depth. In this region, a majority of the deep coal beds are filled with water. The SOTEM technique was successfully employed in detecting the floor of a coal seam at a depth of about 1,500 m, as well as in identifying the location of the water-saturated area. These findings were later confirmed by subsequent drillings. Thus, our study indicates that SOTEM represents a convenient and effective technique for deep mineral and hydrogeological investigations due to its high sensitivity to conductive zones (water enriched areas) and vertical resolution.

Shear Senses and Viscous Dissipation of Layered Ductile Simple Shear Zones

Abstract: Velocity profiles and shear heat profiles for inclined, layered Newtonian simple shear zones are considered. Reverse fault-like simple shear of the boundaries and upward net pressure gradient act together in such shear zones. As the velocity of the boundary increases, the point of highest velocity shifts from the lower layer of less viscosity into the upper layer. The shear heat profile shows a temperature peak inside the lower layer. For a more viscous upper layer, the point of highest velocity is located inside the upper layer and shifts towards the upper boundary of the shear zone. The shear heat profile shows a maximum temperature within the upper layer. Depending on the flow parameters of the two layers, the slip rate of the boundary, and the dip and thickness of the shear zone, a shear sense in reverse to the relative movement of the shear zone boundaries may develop. These models can decipher thermo-kinematics of layered shear zones in plate-scale hot orogens.

A Nonextensive Statistical Physics Analysis of the 1995 Kobe, Japan Earthquake

Abstract: This paper presents an analysis of the distribution of earthquake magnitudes for the period 1990–1998 in a broad area surrounding the epicenter of the 1995 Kobe earthquake. The frequency–magnitude distribution analysis is performed in a nonextensive statistical physics context. The nonextensive parameter qM, which is related to the frequency-magnitude distribution, reflects the existence of long-range correlations and is used as an index of the physical state of the studied area. Examination of the possible variations of qM values is performed during the period 1990–1998. A significant increase of qM occurs some months before the strong earthquake on April 9, 1994 indicating the start of a preparation phase prior to the Kobe earthquake. It should be noted that this increase coincides with the occurrence of six seismic events. Each of these events had a magnitude M = 4.1. The evolution of seismicity along with the increase of qM indicate the system’s transition away from equilibrium and its preparation for energy release. It seems that the variations of qM values reflect rather well the physical evolution towards the 1995 Kobe earthquake.

Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults

Abstract: We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and amplitude coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the amplitude coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Joint Inversion of Seismic and Magnetotelluric Data in the Parkfield Region of California Using the Normalized Cross-Gradient Constraint

Abstract: We present jointly inverted models of P-wave velocity (Vp) and electrical resistivity for a two-dimensional profile centered on the San Andreas Fault Observatory at Depth (SAFOD). Significant structural similarity between main features of the separately inverted Vp and resistivity models is exploited by carrying out a joint inversion of the two datasets using the normalized cross-gradient constraint. This constraint favors structurally similar Vp and resistivity images that adequately fit the seismic and magnetotelluric (MT) datasets. The new inversion code, tomoDDMT, merges the seismic inversion code tomoDD and the forward modeling and sensitivity kernel subroutines of the MT inversion code OCCAM2DMT. TomoDDMT is tested on a synthetic dataset and demonstrates the code’s ability to more accurately resolve features of the input synthetic structure relative to the separately inverted resistivity and velocity models. Using tomoDDMT, we are able to resolve a number of key issues raised during drilling at SAFOD. We are able to infer the distribution of several geologic units including the Salinian granitoids, the Great Valley sequence, and the Franciscan Formation. The distribution and transport of fluids at both shallow and great depths is also examined. Low values of velocity/resistivity attributed to a feature known as the Eastern Conductor (EC) can be explained in two ways: the EC is a brine-filled, high porosity region, or this region is composed largely of clay-rich shales of the Franciscan. The Eastern Wall, which lies immediately adjacent to the EC, is unlikely to be a fluid pathway into the San Andreas Fault’s seismogenic zone due to its observed higher resistivity and velocity values.

Model Space Exploration for Determining Landslide Source History from Long-Period Seismic Data

Abstract: The seismic signals generated by two large volcanic debris avalanches (Montserrat, Lesser Antilles, 1997 and Mount St. Helens, USA, 1980) and a large rock-ice avalanche (Mount Steller, USA, 2005) have been analyzed. For the two debris avalanches, given the times and locations of such landslides, their signals were recorded by only a few seismic stations. Moreover, these signals cover only a very narrow frequency band and include considerable noise. The Mount Steller, on the contrary, was precisely recorded. For each event, the source mechanism (i.e., point force) has been determined by waveform inversion using at most two broadband seismic stations. The resulting force is very difficult to interpret in terms of landslide characteristics. A Monte-Carlo inversion was therefore performed by imposing a simple force model associated with the landslide, based on the schematic view of an accelerating/decelerating mass traveling down the slope. The best parameter set of the force model was then found by minimizing misfits and maximizing correlations between data and synthetic signals. This model appears to contain the minimum degree of complexity required to well reproduce the seismic data. We detail here the method for the Montserrat debris avalanche and then present it’s validation on the well studied Mount St. Helens debris avalanche and the well recorded Mount Steller rock-ice avalanche. The horizontal and vertical components of the resulting force have different source time functions. The best force model compares well with the force obtained by waveform inversion. Finally, this simple force model was interpreted using analytical and empirical relations derived from the sliding block model, granular flow model and landslide studies. This made it possible to estimate the order of magnitude of the mass, flow duration and direction, initial topography slope, mean velocity and travel distance of the avalanches. For these three avalanches, the calculated characteristics are consistent with former studies.

Crustal Thickness of Iran Inferred from Converted Waves

Abstract: The Iranian plate is part of the Alpine-Himalayan orogenic belt, which has been formed by the continental collision between the Arabian and Eurasian plates. The present-day Iranian plate is characterized by diverse tectonic domains including mountain belts (e.g. Zagros and Alborz, Kopeh-Dagh) and oceanic plate subduction (e.g. Makran). Here we present the lateral variations of the Moho discontinuity beneath Iran using a detailed P receiver function study. Our results allow for more precise estimations of the crustal thickness and enable us to provide a detailed Moho depth map for all of Iran for the first time. We used the teleseismic events recorded from 1995 to 2011 at 77 national permanent stations (24 broadband and 53 short period stations). Our results show significant variations in the crustal thickness, which are related to the different geological features within Iran. In general, the average crustal thickness beneath Iran is about 40–45 km. A relatively thick crust of about 54 ± 2 km due to the shortening is observed beneath the Alborz mountain ranges. The crust beneath the Alborz zone shows a thickness changing from 47 ± 2 to 45 ± 2 km from west to east and reaches a thickness of about 50 ± 2 km beneath the Kopeh-Dagh mountain range. We find the thinnest crust of about 33 ± 2 km beneath the Makran subduction zone in southeast Iran showing a normal continental crust, which has not been influenced by collisional processes. The thickest crust (~66 ± 2 km) is locally observed beneath the Sanandaj-Sirjan Zone, which is considered the suture zone of the collision between the Arabian and Eurasian plates.

A Comparison of Seismicity Characteristics and Fault Structure Between Stick–Slip Experiments and Nature

Abstract: Fault zones contain structural complexity on all scales. This complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events. Incomplete earthquake records, unknown stresses, and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity. To better understand the relationship between fault structure and seismicity, we examined dynamic faulting under controlled conditions in the laboratory by creating saw-cut-guided natural fractures in cylindrical granite samples. The resulting rough surfaces were triaxially loaded to produce a sequence of stick–slip events. During these experiments, we monitored stress, strain, and seismic activity. After the experiments, fault structures were imaged in thin sections and using computer tomography. The laboratory fault zones showed many structural characteristics observed in upper crustal faults, including zones of localized slip embedded in a layer of fault gouge. Laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro-crack density at larger distances from the fault axis. In addition to the structural similarities, we also observed many similarities between our observed distribution of acoustic emissions (AEs) and natural seismicity. The AEs followed the Gutenberg–Richter and Omori–Utsu relationships commonly used to describe natural seismicity. Moreover, we observed a connection between along-strike fault heterogeneity and variations of the Gutenberg–Richter b value. As suggested by natural seismicity studies, areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post-experimental tomography scans. Our results emphasize the importance of stick–slip experiments for the study of fault mechanics. The direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature.

Deep-Water Characteristics of the Trans-Pacific Tsunami from the 1 April 2014 M w 8.2 Iquique, Chile Earthquake

Abstract: The sea level data used in this study were provided through the USA National Oceanographic and Atmospheric Administration (NOAA). We thank Hiroshi Tsuruoka and Takeo Ishibe at the Earthquake Research Institute (ERI) for assisting in preparation of some figures. Several figures were drafted using the GMT software (Wessel and Smith 1991). We are sincerely grateful to Prof. Alexander Rabinovich, the editor, and two anonymous reviewers for comments that improved this article. This study is supported by the Japan Society for the Promotion of Science (JSPS).