Directional site resonances and the influence of near-surface geology on ground motion

1991 ◽  
Vol 18 (5) ◽  
pp. 901-904 ◽  
Author(s):  
Ornella Bonamassa ◽  
John E. Vidale ◽  
Heidi Houston ◽  
Susan Y. Schwartz
Keyword(s):  
Ground Motion ◽  
Near Surface ◽  
Surface Geology

scholarly journals Towards a national 3D geological model of Denmark

2016 ◽  
Vol 35 ◽  
pp. 27-30
Author(s):  
Peter B.E. Sandersen ◽  
Thomas Vangkilde-Pedersen ◽  
Flemming Jørgensen ◽  
Richard Thomsen ◽  
Jørgen Tulstrup ◽  
...  
Keyword(s):  
Subsurface Layer ◽  
Geological Model ◽  
Technical Standards ◽  
Near Surface ◽  
Subsurface Geology ◽  
3D Geological Model ◽  
Combining Data ◽  
National Model ◽  
Surface Geology ◽  
2D To 3D

As part of its strategy, the Geological Survey of Denmark and Greenland (GEUS) is to develop a national, digital 3D geological model of Denmark that can act as a publicly accessible database representing the current, overall interpretation of the subsurface geology. A national model should be under constant development, focusing on meeting the current demands from society. The constant improvements in computer capacity and software capabilities have led to a growing demand for advanced geological models and 3D maps that meet the current technical standards (Berg et al. 2011). As a consequence, the users expect solutions to still more complicated and sophisticated problems related to the subsurface. GEUS has a long tradition of making 2D maps of subsurface layer boundaries and near-surface geology (Fredericia & Gravesen 2014), but in the change from 2D to 3D and when combining data in new ways, new geological knowledge is gained and new challenges of both technical and organisational character will arise. The purpose of this paper is to present the strategy for the national 3D geological model of Denmark and the planned activities for the years ahead. The paper will also reflect on some of the challenges related to making and maintaining a nationwide 3D model. Initially, the model will only include the Danish onshore areas, with the Danish offshore areas and Greenland to be added later using a similar general setup.

scholarly journals Basin Resonance and Seismic Hazard for Jakarta, Indonesia

2018 ◽  
Author(s):  
Athanasius Cipta ◽  
Phil Cummins ◽  
Masyhur Irsyam ◽  
Sri Hidayati
Keyword(s):  
Ground Motion ◽  
Seismic Waves ◽  
Response Spectrum ◽  
Capital City ◽  
Earthquake Ground Motion ◽  
Computational Domain ◽  
Near Surface ◽  
Earthquake Scenario ◽  
Design Response Spectrum ◽  
Intraslab Earthquake

We use earthquake ground motion modelling via Ground Motion Prediction Equations (GMPEs) and numerical simulation of seismic waves to consider the effects of site amplification and basin resonance in Jakarta, the capital city of Indonesia. While spectral accelerations at short periods are sensitive to near-surface conditions (i.e., Vs30), our results suggest that, for basins as deep as Jakarta’s, available GMPEs cannot be relied upon to accurately estimate the effect of basin depth on ground motions at long periods (>1 s). Amplitudes at such long periods are influenced by entrapment of seismic waves in the basin, resulting in longer duration of strong ground motion, and interference between incoming and reflected waves as well as focusing at basin edges may amplify seismic waves. In order to simulate such phenomena in detail, a basin model derived from a previous study is used as a computational domain for deterministic earthquake scenario modeling in a 2-dimensional cross-section. A Mw 9.0 megathrust, a Mw 6.5 crustal thrust and a Mw 7.0 instraslab earthquake are chosen as scenario events that pose credible threats to Jakarta, and the interactions with the basin of seismic waves generated by these events were simulated. The highest PGV amplifications are recorded at sites near the middle of the basin and near its southern edge, with maximum amplifications of PGV in the horizontal component of 200% for the crustal, 600% for the megathrust and 335% for the deep intraslab earthquake scenario, respectively. We find that the levels of ground motion response spectral acceleration fall below those of the 2012 Indonesian building Codes's design response spectrum for short periods (< 1 s), but closely approach or may even exceed these levels for longer periods.

Rainfall-Induced Variation of Seismic Waves Velocity in Soil and Implications for Soil Response: What the ARGONET (Cephalonia, Greece) Vertical Array Data Reveal

2020 ◽  
Vol 110 (2) ◽  
pp. 441-451
Author(s):  
Zafeiria Roumelioti ◽  
Fabrice Hollender ◽  
Philippe Guéguen
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Surface Velocity ◽  
Depth Interval ◽  
Seasonal Effect ◽  
Surface Wave Dispersion ◽  
Near Surface ◽  
Soil Response ◽  
Earthquake Records ◽  
Shallow Sediments

ABSTRACT We apply interferometry by deconvolution to compute the shear-wave velocity in shallow sediments (0–83.4 m) based on earthquake records from a vertical accelerometric array (ARGOstoli Network [ARGONET]) on Cephalonia Island, Greece. Analysis of the time variation of measured values reveals a cyclical pattern, which correlates negatively to rainfall and a soil moisture proxy. The pattern includes a sharp reduction in velocity at the beginning of rainy seasons and a gradual rise toward dry periods, the overall variation being around 20%–25% within the shallowest depth interval examined (0–5.6 m) and estimated to reach 40% within the top 2 m. The variation itself and its amplitude are verified by surface-wave dispersion analysis, using ambient vibration data. Synthetic standard spectral ratios suggest that this seasonal effect leaves an imprint on soil response, causing differences in the level of high-frequency ground motion between dry and rainy seasons, and this is verified by earthquake records. Furthermore, the near-surface velocity decrease due to soil saturation can be of the same order of magnitude as the nonlinear coseismic variation, masking the physical process of the nonlinear response of the site due to weak-to-strong-motion shaking. Thus, seasonal variations of seismic-wave velocities in shallow sediments may be important for a number of site-effect related topics, such as high-frequency ground-motion variability, soil anisotropy, kappa measurements, nonlinear site response, and so on.

scholarly journals Regional-Scale 3D Ground-Motion Simulations of Mw 7 Earthquakes on the Hayward Fault, Northern California Resolving Frequencies 0–10 Hz and Including Site-Response Corrections

2020 ◽  
Vol 110 (6) ◽  
pp. 2862-2881
Author(s):  
Arthur J. Rodgers ◽  
Arben Pitarka ◽  
Ramesh Pankajakshan ◽  
Bjorn Sjögreen ◽  
N. Anders Petersson
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Regional Scale ◽  
Frequency Resolution ◽  
Earthquake Ground Motion ◽  
Northern California ◽  
Soft Soils ◽  
Near Surface ◽  
Ground Motion Simulations ◽  
Scenario Earthquakes

ABSTRACT Large earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500  m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500  m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

scholarly journals Characterization of a complex near-surface structure using well logging and passive seismic measurements

2016 ◽  
Author(s):  
Beatriz Benjumea ◽  
Albert Macau ◽  
Anna Gabàs ◽  
Sara Figueras
Keyword(s):  
Wave Velocity ◽  
Upper Cretaceous ◽  
Seismic Velocity ◽  
Well Logging ◽  
P Wave ◽  
Geophysical Field ◽  
Near Surface ◽  
Passive Seismic ◽  
Surface Geology ◽  
Seismic Measurements

Abstract. We combine geophysical well logging and passive seismic measurements to characterize the near surface geology of an area located in Hontomin, Burgos (Spain). This area has some near-surface challenges for a geophysical study. The irregular topography is characterized by limestone outcrops and unconsolidated sediments areas. Additionally, the near surface geology includes an upper layer of pure limestones overlying marly limestones and marls (Upper Cretaceous). These materials lie on top of Low Cretaceous siliciclastic sediments (sandstones, clays, gravels). In any case, decreasing seismic velocity with depth is expected. The geophysical datasets used in this study include sonic and gamma ray logs at two boreholes and passive seismic measurements: 224 H/V stations and 3 arrays. Well logging data defines two significant changes in the P-wave velocity log within the Upper Cretaceous layer and one more at the Upper to Lower Cretaceous contact. This technique has also used for refining the geological interpretation. The passive seismic measurements provide a map of sediment thickness with maximum of around 40 m and shear-wave velocity profiles from the array technique. A comparison between seismic velocity coming from well logging and array measurements defines the resolution limits of the passive seismic techniques and helps for its interpretation. This study shows how these low-cost techniques can provide useful information about near-surface complexity that could be used for designing a geophysical field survey or for seismic processing steps such as statics or imaging.

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