Inferring earth structure from combined measurements of rotational and translational ground motions

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCD41-WCD47 ◽  
Author(s):  
Moritz Bernauer ◽  
Andreas Fichtner ◽  
Heiner Igel
Keyword(s):  
Seismic Tomography ◽  
Wave Speed ◽  
Ground Motions ◽  
Regional Scale ◽  
S Wave ◽  
Tomographic Images ◽  
Teleseismic Tomography ◽  
Local Structures ◽  
Novel Variant ◽  
Definition Of

We introduce a novel variant of seismic tomography that is based on colocated measurements of rotational and translational ground motions. Our aim is to assess whether rotations may be incorporated successfully into seismic inverse problems to produce better resolved and more realistic tomographic images. Our methodology is based on the definition of apparent S-wave speed as the ratio of rms velocity and rotation amplitudes. The principal advantages of this definition are that (1) no traveltimes measurements are needed and (2) the apparent S-wave speed is independent of source magnitude and source timing. We derive finite-frequency kernels for apparent S-wave speed by using a combination of the adjoint method and ray approximation. The properties of these kernels as a function of frequency bandwidth can be illustrated along with their usefulness for seismic tomography. In multifrequency synthetic inversions, we consider local crosshole tomography and regional-scale earthquake tomography. Our results indicate that S-wave speed variations can be retrieved accurately from colocated rotation and translation measurements, suggesting that our methodology is a promising extension of conventional seismic tomography. Further, apparent S-wave speed can be used to increase vertical resolution in teleseismic tomography for local structures.

scholarly journals Coupling of regional geophysics and local soil-structure models in the EQSIM fault-to-structure earthquake simulation framework

2021 ◽  
pp. 109434202110191
Author(s):  
David McCallen ◽  
Houjun Tang ◽  
Suiwen Wu ◽  
Eric Eckert ◽  
Junfei Huang ◽  
...  
Keyword(s):  
Soil Structure ◽  
Ground Motions ◽  
Regional Scale ◽  
Historical Earthquakes ◽  
Department Of Energy ◽  
Simulation Framework ◽  
Data Set ◽  
Major Barrier ◽  
Local Soil ◽  
Computational Workflow

Accurate understanding and quantification of the risk to critical infrastructure posed by future large earthquakes continues to be a very challenging problem. Earthquake phenomena are quite complex and traditional approaches to predicting ground motions for future earthquake events have historically been empirically based whereby measured ground motion data from historical earthquakes are homogenized into a common data set and the ground motions for future postulated earthquakes are probabilistically derived based on the historical observations. This procedure has recognized significant limitations, principally due to the fact that earthquake ground motions tend to be dictated by the particular earthquake fault rupture and geologic conditions at a given site and are thus very site-specific. Historical earthquakes recorded at different locations are often only marginally representative. There has been strong and increasing interest in utilizing large-scale, physics-based regional simulations to advance the ability to accurately predict ground motions and associated infrastructure response. However, the computational requirements for simulations at frequencies of engineering interest have proven a major barrier to employing regional scale simulations. In a U.S. Department of Energy Exascale Computing Initiative project, the EQSIM application development is underway to create a framework for fault-to-structure simulations. This framework is being prepared to exploit emerging exascale platforms in order to overcome computational limitations. This article presents the essential methodology and computational workflow employed in EQSIM to couple regional-scale geophysics models with local soil-structure models to achieve a fully integrated, complete fault-to-structure simulation framework. The computational workflow, accuracy and performance of the coupling methodology are illustrated through example fault-to-structure simulations.

Dynamic Analysis of a Mode I Propagating Crack Subjected to a Concentrated Load

2003 ◽  
Vol 70 (5) ◽  
pp. 668-675
Author(s):  
Y.-L. Chung ◽  
M.-R. Chen
Keyword(s):  
Stress Intensity ◽  
Wave Speed ◽  
Complete Solution ◽  
Crack Tip ◽  
Dynamic Effect ◽  
Mode I ◽  
S Wave ◽  
Dynamic Stress Intensity Factors ◽  
Concentrated Load ◽  
Self Similar

This work investigates the phenomenon of mode I central crack propagating with a constant speed subjected to a concentrated load on the crack surfaces. This problem is not a self-similar problem. However, the method of self-similar potential (SSP) in conjunction with superposition can be successfully applied if the time delay and the origin shift are considered. After the complete solution is obtained, attention is stressed on the dynamic stress intensity factors (DSIFs). Analytical results indicate that the DSIF equals the static stress intensity factor if the crack-tip speed is very slow and equal to zero if the crack-tip velocity approaches the Rayleigh-wave speed. However, the dynamic effect becomes obvious only if the crack-tip speed is 0.4 times faster than the S-wave speed. Moreover, the combination of SSP method and the superposition scheme can be applied to the expanding uniformly distributed load acting on a portion of the crack surfaces.

scholarly journals Seismogenic nodes as a viable alternative to seismogenic zones and observed seismicity for the definition of seismic hazard at regional scale

2019 ◽  
Vol 41 (4) ◽  
pp. 289-304 ◽  
Author(s):  
Paolo Rugarli ◽  
Franco Vaccari ◽  
Giuliano Panza
Keyword(s):  
Seismic Hazard ◽  
Safety Factor ◽  
Seismic Moment ◽  
Regional Scale ◽  
Seismic Hazard Assessment ◽  
Hazard Maps ◽  
Earthquake Catalogues ◽  
Definition Of ◽  
Partial Factor ◽  
Seismogenic Nodes

A fixed increment of magnitude is equivalent to multiply the seismic moment by a factor γEM related to the partial factor γq acting on the seismic moment representing the fault. A comparison is made between the hazard maps obtained with the Neo-Deterministic Seismic Hazard Assessment (NDSHA), using two different approaches: one based on the events magnitude, listed in parametric earthquake catalogues compiled for the study areas, with sources located within the seismogenic zones; the other uses the seismogenic nodes identified by means of pattern recognition techniques applied to morphostructural zonation (MSZ), and increases the reference magnitude by a constant amount tuned by the safety factor γEM.Using γEM=2.0, in most of the territory the two approaches produce totally independent, comparable hazard maps, based on the quite long Italian catalogue. This represents a validation of the seismogenic nodes method and a tuning of the safety factor γEM at about 2.

Geostatistical approach for multi-scale seismic liquefaction risk assessment

2021 ◽  
Author(s):  
Rose Line Spacagna ◽  
Massimo Cesarano ◽  
Stefania Fabozzi ◽  
Edoardo Peronace ◽  
Attilio Porchia ◽  
...  
Keyword(s):  
Regional Scale ◽  
Morphological Characteristics ◽  
Predisposing Factors ◽  
Data Availability ◽  
Hazard Maps ◽  
Multi Scale ◽  
Seismic Liquefaction ◽  
Research Activities ◽  
Geostatistical Approach ◽  
Definition Of

<p>The Seismic Microzonation studies (SMs), promoted all over the Italian territory by the Department of Civil Protection, provide fundamental knowledge of the subsoil response in seismic conditions at the urban scale. Amplification phenomena related to lithostratigraphic and morphological characteristics, instabilities and permanent deformations activated by the earthquake, are highlighted in hazard maps produced at increasing reliability levels (level 1 to 3 of SM). In particular, zones prone to liquefaction instability are firstly identified following the predisposing factors, such as geological and geotechnical characteristics and seismicity. The robustness of the definition of these areas is strongly correlated to the availability and the spatial distribution of surveys. Moreover, the typology and quality of the investigations considerably influence the method of analysis and the degree of uncertainty of the results.</p><p>This work aims to establish an updated procedure of the actual SM guidelines and integrates recent research activities at different levels of SMs, to improve the hazard maps accuracy in terms of liquefaction susceptibility. For the scope, the case of the Calabria region in the south of Italy, well known for the high level of seismicity, was studied. At a regional scale, the base-level analysis was implemented for a preliminary assessment of the Attention Zones (AZ), potentially susceptible to liquefaction. The predisposing factors were implemented at a large scale, taking advantage of geostatistical tools to quantify uncertainties and filter inconsistent data. The regional-scale analysis allowed to highlight areas prone to liquefaction and effectively addressed the subsequent level of analysis. At a local scale, the quantitative evaluation of the liquefaction potential was assessed using simplified methods, integrating data from different survey types (CPT, SPT, Down-Hole, Cross-Hole, MASW) available in SM database. The definition of Susceptibility Zones (SZ) was provided considering additional indexes, combining the results obtained from different surveys typologies and quantifying the uncertainty due to the limited data availability with geostatistical methods. The analyses at the regional and municipality scale were matched with seismic liquefaction evidence, well documented in past seismic events. This multi-scale process optimises resource allocation to reduce the level of uncertainty for subsequent levels of analysis, providing useful information for land management and emergency planning.</p>

Landscape Influences on Stream Habitats and Biological Assemblages

2006 ◽  
Keyword(s):  
Total Phosphorus ◽  
Human Disturbance ◽  
Regional Scale ◽  
Vertebrate Species ◽  
Catchment Scale ◽  
Human Disturbances ◽  
Disturbed Condition ◽  
Small Streams ◽  
Definition Of ◽  
Assemblage Metrics

<em>Abstract.</em>—At broad scales, the types and intensities of human disturbances to ecosystems vary along natural gradients. Biological assemblages also vary with natural and human disturbance gradients. We defined least-disturbed conditions for a set of water chemistry, catchment, and site-scale indicators of disturbance, for 835 Environmental Monitoring and Assessment Program sites in the Mountains, Xeric, and Plains regions of 12 conterminous western United States. For each disturbance indicator, the definition of least-disturbed was adjusted by the sites’ locations on the primary natural gradients. For example, the least-disturbed condition for phosphorus in eastern Plains streams allowed up to 100 µg/L total phosphorus, while in western Plains streams, less than 30 µg/L total phosphorus was required. Sites were scored by the number of times they met the least-disturbed condition for all disturbance indicators. We also applied this process to score for most-disturbed condition. The importance of disturbance types varied regionally and along natural gradients. For example, catchment-scale disturbance measures did not distinguish between least- and most-disturbed sites for small streams at higher elevations, but were important for larger streams and at lower elevations. We examined regional-scale patterns in aquatic vertebrate species and assemblage metrics, and macrobenthos assemblage metrics at least- and most-disturbed sites. Most-disturbed sites in the Mountains and Xeric regions had higher proportions of nonnative and tolerant vertebrates and noninsect macrobenthos, and lower proportions of Ephemeroptera, Plecoptera, and Trichoptera individuals and taxa than did the least-disturbed sites. The Plains region has been extensively used by humans and showed less contrast between disturbance classes for most of these measures.

scholarly journals Capturing Regional Variations of Hard‐Rock Attenuation in Europe

2019 ◽  
Vol 109 (4) ◽  
pp. 1401-1418 ◽  
Author(s):  
Marco Pilz ◽  
Fabrice Cotton ◽  
Riccardo Zaccarelli ◽  
Dino Bindi
Keyword(s):  
High Frequency ◽  
Hard Rock ◽  
Epistemic Uncertainty ◽  
Ground Motions ◽  
Soft Soil ◽  
Coda Waves ◽  
Corner Frequency ◽  
S Wave ◽  
Empirical Parameter ◽  
Regional Variations

Abstract A proper assessment of seismic reference site conditions has important applications as they represent the basis on which ground motions and amplifications are generally computed. Besides accounting for the average S‐wave velocity over the uppermost 30 m (VS30), the parameterization of high‐frequency ground motions beyond source‐corner frequency received significant attention. κ, an empirical parameter introduced by Anderson and Hough (1984), is often used to represent the spectral decay of the acceleration spectrum at high frequencies. The lack of hard‐rock records and the poor understanding of the physics of κ introduced significant epistemic uncertainty in the final seismic hazard of recent projects. Thus, determining precise and accurate regional hard‐rock κ0 values is critical. We propose an alternative procedure for capturing the reference κ0 on regional scales by linking the well‐known high‐frequency attenuation parameter κ and the properties of multiple‐scattered coda waves. Using geological and geophysical data around more than 1300 stations for separating reference and soft soil sites and based on more than 10,000 crustal earthquake recordings, we observe that κ0 from multiple‐scattered coda waves seems to be independent of the soil type but correlated with the hard‐rock κ0, showing significant regional variations across Europe. The values range between 0.004 s for northern Europe and 0.020 s for the southern and southeastern parts. On the other hand, measuring κ (and correspondingly κ0) on the S‐wave window (as classically proposed), the results are strongly affected by transmitted (reflected, refracted, and scattered) waves included in the analyzed window biasing the proper assessment of κ0. This effect is more pronounced for soft soil sites. In this way, κ0coda can serve as a proxy for the regional hard‐rock κ0 at the reference sites.

NEW DIRECTIONS IN GEOSCIENCE TECHNOLOGY FOR PETROLEUM EXPLORATION IN THE NEW AGE

1994 ◽  
Vol 34 (1) ◽  
pp. 189
Author(s):  
T. L. Burnett
Keyword(s):  
Oil And Gas ◽  
Regional Scale ◽  
Seismic Energy ◽  
Oil And Gas Industry ◽  
Transport Processes ◽  
Source Rocks ◽  
P Wave ◽  
Petroleum Exploration ◽  
S Wave ◽  
Seismic Acquisition

As economics of the oil and gas industry become more restrictive, the need for new means of improving exploration risks and reducing expenses is becoming more acute. Partnerships between industry and academia are making significant improvements in four general areas: Seismic acquisition, reservoir characterisation, quantitative structural modelling, and geochemical inversion.In marine seismic acquisition the vertical cable concept utilises hydrophones suspended at fixed locations vertically within the water column by buoys. There are numerous advantages of vertical cable technology over conventional 3-D seismic acquisition. In a related methodology, 'Borehole Seismic', seismic energy is passed between wells and valuable information on reservoir geometry, porosity, lithology, and oil saturation is extracted from the P-wave and S-wave data.In association with seismic methods of determining the external geometry and the internal properties of a reservoir, 3-dimensional sedimentation-simulation models, based on physical, hydrologic, erosional and transport processes, are being utilised for stratigraphic analysis. In addition, powerful, 1-D, coupled reaction-transport models are being used to simulate diagenesis processes in reservoir rocks.At the regional scale, the bridging of quantitative structural concepts with seismic interpretation has led to breakthroughs in structural analysis, particularly in complex terrains. Such analyses are becoming more accurate and cost effective when tied to highly advanced, remote-sensing, multi-spectral data acquisition and image processing technology. Emerging technology in petroleum geochemistry, enables geoscientists to infer the character, age, maturity, identity and location of source rocks from crude oil characteristics ('Geochemical Inversion') and to better estimate hydrocarbon-supply volumetrics. This can be invaluable in understanding petroleum systems and in reducing exploration risks and associated expenses.

scholarly journals Application of seismic tomography for detecting structural faults in a Tertiary Formation

2019 ◽  
Vol 92 ◽  
pp. 18008
Author(s):  
Víctor A. Rinaldi ◽  
Horacio V. Ibarra ◽  
Ricardo F. Viguera ◽  
Juan C. Harasimiuk
Keyword(s):  
Seismic Tomography ◽  
Seismic Refraction ◽  
Soil Formation ◽  
Seismic Profile ◽  
Basic Principles ◽  
Geotechnical Parameters ◽  
Tomographic Images ◽  
The North ◽  
History Of ◽  
Good Agreement

Seismic refraction technique is an increasingly useful geophysical tool for geotechnical studies in civil engineering work including the mapping of different soil formation of subsoil and detection of the bed rock. Additionally, wave velocity is a key parameter which correlates directly with significant geotechnical parameters of soils and rocks. Today, the evolution of the measurement technique in the field and the data processing allows to obtain tomographic images which increases its potential for applications to evaluate structuration of rock mass. This work describes the basic principles of seismic tomography and a case history of an application in civil works used to detect hidden faults in the sedimentary Gatun formation at the north of Panama. The correlation between the seismic profile and geologic profile obtained from boreholes showed very good agreement. Subsequent directed boreholes performed at the site confirmed the position and nature of the faults detected.

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