Horizontal-to-vertical spectral ratio and geological conditions: The case of Garner Valley Downhole Array in southern California

1996 ◽  
Vol 86 (2) ◽  
pp. 306-319 ◽  
Author(s):  
N. Theodulidis ◽  
P.-Y. Bard ◽  
R. Archuleta ◽  
M. Bouchon
Keyword(s):  
Southern California ◽  
Transfer Functions ◽  
High Sensitivity ◽  
Spectral Ratio ◽  
S Wave ◽  
Absolute Level ◽  
Data Set ◽  
Geological Conditions ◽  
Different Depths ◽  
Downhole Array

Abstract The aim of the present article is to further check the use of the horizontal-to-vertical (h/v) spectral ratio, which has been recently suggested as an indicator of site effects. The data set consists of 110, three-component, high sensitivity accelerograms, recorded at five different depths by the Garner Valley Downhole Array (GVDA), in southern California, with peak ground accelerations 0.0002 g ≦ ag ≦ 0.04 g, magnitudes 3.0 ≦ ML ≦ 4.6, and hypocentral distances 16 km ≦ R ≦ 107 km. First, the stability of the (h/v) spectral ratio is investigated by computing the mean for the whole data set in different depths. The (h/v) spectral ratio on the surface is compared with the surface-to-depth standard spectral ratio, with theoretical S-wave transfer functions derived from the vertical geotechnical profile, as well as with the (h/v) spectral ratio of synthetic accelerograms generated by the discrete wavenumber method. Both theoretical and experimental data show a good stability of the (h/v) spectral ratio shape, which is in good agreement with the local geological structure and is insensitive to the source location and mechanism. However, the absolute level of the (h/v) spectral ratio depends on the wave field and is different from the surface-to-depth spectral ratio. Consequently the (h/v) spectral ratio technique provides only partially the information that can be obtained from a downhole array. But surface-to-depth ratios may also be misleading because they combine effects at surface and at depth.

Data Analysis of the Euroseistest Strong Motion Array in Volvi (Greece): Standard and Horizontal-to-Vertical Spectral Ratio Techniques

1998 ◽  
Vol 14 (1) ◽  
pp. 203-224 ◽  
Author(s):  
D. Raptakis ◽  
N. Theodulidis ◽  
K. Pitilakis
Keyword(s):  
Resonant Frequency ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Absolute Level ◽  
Data Set ◽  
Alluvial Deposits ◽  
Standard Spectral Ratio ◽  
Strong Motion Station ◽  
Geological Conditions

In this study, the standard spectral ratio and the horizontal-to-vertical spectral ratio techniques are applied in order to study their effectiveness in investigating and quantifying the influence of geological conditions on strong ground motion. For this purpose, an accelerogram data set recorded at the Euroseistest array in the Mygdonia graben (lake Volvi area) near Thessaloniki, Greece, during the period April 1994 to June 1996 is used. Both experimental techniques show similar spectral ratio shapes with comparable fundamental resonant frequencies, which are well correlated with the well known geotechnical-geological conditions. Namely, the resonant frequency at the center of the valley is shifted to lower values, less than 1 Hz, while at the edge it is shifted to higher values, greater than 2 Hz. The horizontal-to-vertical spectral ratio technique is an effective method to estimate some basic characteristics of local site effects using a single accelerograph station. It reveals the fundamental resonant frequency of alluvial deposits by using only a single strong motion station, while the absolute level of the horizontal-to-vertical spectral ratio method tends to underestimate the amplification level compared to the standard spectral ratio technique.

The Importance of Distinguishing Pseudoresonances and Outcrop Resonances in Downhole Array Data

2019 ◽  
Vol 110 (1) ◽  
pp. 288-294 ◽  
Author(s):  
Yumeng Tao ◽  
Ellen Rathje
Keyword(s):  
Transfer Functions ◽  
Site Response ◽  
Short Note ◽  
Spectral Ratio ◽  
Site Response Analysis ◽  
Response Analysis ◽  
Frequency Range ◽  
Wave Effect ◽  
Array Data ◽  
Downhole Array

ABSTRACT This short note examines the downgoing wave effect and the appearance of pseudoresonances in downhole array data. It is demonstrated that pseudoresonances, distinct from the resonances associated with outcrop conditions, occur for sites with a shallow velocity contrast (VC) or with little to no VC. An approach is outlined to distinguish pseudoresonances from outcrop resonances using the theoretical 1D transfer functions for within and outcrop boundary conditions, as well as the horizontal-to-vertical spectral ratio. This approach is applied to hypothetical shear-wave velocity profiles, as well as three downhole array sites. We establish the importance of distinguishing pseudoresonances from outcrop resonances when using downhole array data to evaluate the accuracy of the 1D site response. For the example downhole array sites shown, the pseudoresonances are not captured well by 1D analysis, whereas the outcrop resonances are captured well. We propose that when evaluating the accuracy of 1D site-response analysis using downhole array data, the comparisons of the empirical and theoretical responses only consider the frequency range associated with outcrop resonances.

Site-dependent attenuation relations of seismic motion parameters at depth using borehole data

1995 ◽  
Vol 85 (6) ◽  
pp. 1790-1804
Author(s):  
Yoshimitsu Fukushima ◽  
Jean-Christophe Gariel ◽  
Ryozo Tanaka
Keyword(s):  
Transfer Functions ◽  
Ground Surface ◽  
Response Spectra ◽  
Borehole Data ◽  
Ground Acceleration ◽  
Attenuation Relations ◽  
Attenuation Relationships ◽  
Geological Conditions ◽  
Velocity Response ◽  
Different Depths

Abstract Using more than 500 accelerometric records from three vertical arrays located in Japan, we performed a regression analysis in order to derive attenuation relationships at underground sites with depths ranging from 100 to 950 m. Analyses were conducted on both peak ground acceleration and pseudo-velocity response spectra. Because of a positive correlation between magnitude and distance, a two-step regression technique was employed. Results show that, compared with surface ground motion, peak accelerations at underground sites are lower by a factor ranging from 1.5 to 4 according to the depth. In the case of response spectra, differences between ground surface and underground spectra are dependent on geological conditions. For the three sites considered in the study, underground pseudo-velocity response spectra show amplitudes lower by a factor ranging from 1.5 to 10 according to the depth or the period considered. Ratios between the receiver responses obtained at different depths provided average transfer functions. Those were compared with transfer functions calculated by averaging ratios of observed response spectra between different depths. A good agreement between the two techniques was found. Finally, theoretical transfer functions were estimated using both one-dimensional SH and complete wave modeling. It was shown that the characteristics of the incident wave field can play an important role in the estimation of theoretical transfer functions.

High-frequency borehole seismograms recorded in the San Jcinto Fault zone, Southern California Part 2. Attenuation and site effects

1991 ◽  
Vol 81 (4) ◽  
pp. 1081-1100 ◽  
Author(s):  
Richard C. Aster ◽  
Peter M. Shearer
Keyword(s):  
Fault Zone ◽  
High Frequency ◽  
Southern California ◽  
Spectral Ratio ◽  
Seismic Signals ◽  
Noise Levels ◽  
S Wave ◽  
Low Velocity ◽  
High Frequency Signal ◽  
Near Surface

Abstract We examine surface and downhole P- and S-wave spectra from local earthquakes recorded at two borehole seismometer arrays (KNW-BH and PFO-BH) installed in the Southern California Batholith region of the San Jacinto Fault zone by the U.S. Geological Survey to assess the influence of the weathered layer on the spectral content of high-frequency (2 to 200 Hz) seismic signals. Earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and (especially) to dramatically increased levels of high-frequency signal. Significant seismic signal is observed up to approximately 190 Hz for P waves at KNW-BH. Stacked spectral ratios from these signals indicate that the highly weathered near-surface (between 0 and 150 m) at KNW-BH and PFO-BH exerts a much larger influence on seismic signals than deeper (between 150 and 300 m) material. Modeling of uphole/downhole spectral ratio data suggests Qα ≈ 6.5 and Qβ ≈ 9 between 0 and 150 m, increasing to Qα ≈ 27 and Qβ ≳ 26 between 150 and 300 m. An outcrop-mounted Anza network station, deployed approximately 0.4 km from KNW-BH, displays roughly similar high-frequency content to the KNW-BH downhole sensors, but it exhibits spectra that are significantly colored by directional resonances. Low-Q and low-velocity near-surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high-frequency downhole environment; not only are noise levels reduced, but reflections from the surface and near-surface are greatly attenuated. As a result, high-frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected.

Spectroscopy-Based Mapping with Scanning Microwave Impedance Microscopy

2018 ◽  
Author(s):  
Peter De Wolf ◽  
Zhuangqun Huang ◽  
Bede Pittenger
Keyword(s):  
Single Point ◽  
Electrical Characterization ◽  
Principal Component ◽  
High Sensitivity ◽  
Data Cube ◽  
Nanometer Scale ◽  
Learning Approaches ◽  
Data Set ◽  
3D Data ◽  
Higher Dimensional

Abstract Methods are available to measure conductivity, charge, surface potential, carrier density, piezo-electric and other electrical properties with nanometer scale resolution. One of these methods, scanning microwave impedance microscopy (sMIM), has gained interest due to its capability to measure the full impedance (capacitance and resistive part) with high sensitivity and high spatial resolution. This paper introduces a novel data-cube approach that combines sMIM imaging and sMIM point spectroscopy, producing an integrated and complete 3D data set. This approach replaces the subjective approach of guessing locations of interest (for single point spectroscopy) with a big data approach resulting in higher dimensional data that can be sliced along any axis or plane and is conducive to principal component analysis or other machine learning approaches to data reduction. The data-cube approach is also applicable to other AFM-based electrical characterization modes.

scholarly journals Fall incidents in nursing home residents: development of a predictive clinical rule (FINDER)

BMJ Open ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. e042941
Author(s):  
Vanja Milosevic ◽  
Aimee Linkens ◽  
Bjorn Winkens ◽  
Kim P G M Hurkens ◽  
Dennis Wong ◽  
...  
Keyword(s):  
Nursing Home ◽  
Fall Risk ◽  
Nursing Home Residents ◽  
High Sensitivity ◽  
Secondary Outcome ◽  
Operating Characteristics ◽  
Retrospective Case ◽  
Data Set ◽  
Fall Incident ◽  
Clinical Rule

ObjectivesTo develop (part I) and validate (part II) an electronic fall risk clinical rule (CR) to identify nursing home residents (NH-residents) at risk for a fall incident.DesignObservational, retrospective case–control study.SettingNursing homes.ParticipantsA total of 1668 (824 in part I, 844 in part II) NH-residents from the Netherlands were included. Data of participants from part I were excluded in part II.Primary and secondary outcome measuresDevelopment and validation of a fall risk CR in NH-residents. Logistic regression analysis was conducted to identify the fall risk-variables in part I. With these, three CRs were developed (ie, at the day of the fall incident and 3 days and 5 days prior to the fall incident). The overall prediction quality of the CRs were assessed using the area under the receiver operating characteristics (AUROC), and a cut-off value was determined for the predicted risk ensuring a sensitivity ≥0.85. Finally, one CR was chosen and validated in part II using a new retrospective data set.ResultsEleven fall risk-variables were identified in part I. The AUROCs of the three CRs form part I were similar: the AUROC for models I, II and III were 0.714 (95% CI: 0.679 to 0.748), 0.715 (95% CI: 0.680 to 0.750) and 0.709 (95% CI: 0.674 to 0.744), respectively. Model III (ie, 5 days prior to the fall incident) was chosen for validation in part II. The validated AUROC of the CR, obtained in part II, was 0.603 (95% CI: 0.565 to 0.641) with a sensitivity of 83.41% (95% CI: 79.44% to 86.76%) and a specificity of 27.25% (95% CI 23.11% to 31.81%).ConclusionMedication data and resident characteristics alone are not sufficient enough to develop a successful CR with a high sensitivity and specificity to predict fall risk in NH-residents.Trial registration numberNot available.

A comparison of neustonic plastic and zooplankton at different depths near the southern California shore

2004 ◽  
Vol 49 (4) ◽  
pp. 291-294 ◽  
Author(s):  
G.L. Lattin ◽  
C.J. Moore ◽  
A.F. Zellers ◽  
S.L. Moore ◽  
S.B. Weisberg
Keyword(s):  
Southern California ◽  
Different Depths

A hybrid regularization scheme for the inversion of magnetotelluric data from natural and controlled sources to layer and distortion parameters

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. E301-E315 ◽  
Author(s):  
Thomas Kalscheuer ◽  
Juliane Hübert ◽  
Alexey Kuvshinov ◽  
Tobias Lochbühler ◽  
Laust B. Pedersen
Keyword(s):  
Transfer Functions ◽  
Homogeneous Distribution ◽  
Stable Configuration ◽  
Inversion Algorithm ◽  
Magnetotelluric Data ◽  
Data Set ◽  
Near Surface ◽  
Minimum Solution ◽  
Magnetic Transfer ◽  
Distortion Parameters

Magnetotelluric (MT), radiomagnetotelluric (RMT), and, in particular, controlled-source audiomagnetotelluric (CSAMT) data are often heavily distorted by near-surface inhomogeneities. We developed a novel scheme to invert MT, RMT, and CSAMT data in the form of scalar or tensorial impedances and vertical magnetic transfer functions simultaneously for layer resistivities and electric and magnetic galvanic distortion parameters. The inversion scheme uses smoothness constraints to regularize layer resistivities and either Marquardt-Levenberg damping or the minimum-solution length criterion to regularize distortion parameters. A depth of investigation range is estimated by comparing layered model sections derived from first- and second-order smoothness constraints. Synthetic examples demonstrate that earth models are reconstructed properly for distorted and undistorted tensorial CSAMT data. In the inversion of scalar CSAMT data, such as the determinant impedance or individual tensor elements, the reduced number of transfer functions inevitably leads to increased ambiguity for distortion parameters. As a consequence of this ambiguity for scalar data, distortion parameters often grow over the iterations to unrealistic absolute values when regularized with the Marquardt-Levenberg scheme. Essentially, compensating relationships between terms containing electric and/or magnetic distortion are used in this growth. In a regularization with the minimum solution length criterion, the distortion parameters converge into a stable configuration after several iterations and attain reasonable values. The inversion algorithm was applied to a CSAMT field data set collected along a profile over a tunnel construction site at Hallandsåsen, Sweden. To avoid erroneous inverse models from strong anthropogenic effects on the data, two scalar transfer functions (one scalar impedance and one scalar vertical magnetic transfer function) were selected for inversion. Compared with a regularization of distortion parameters with the Marquardt-Levenberg method, the minimum-solution length criterion yielded smaller absolute values of distortion parameters and a horizontally more homogeneous distribution of electrical conductivity.

P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, southern California: Implications for structure and source location

1996 ◽  
Vol 86 (2) ◽  
pp. 470-476 ◽  
Author(s):  
Cheng-Horng Lin ◽  
S. W. Roecker
Keyword(s):  
Southern California ◽  
Seismic Array ◽  
P Wave ◽  
Small Aperture ◽  
Data Set ◽  
Single Interface ◽  
Seismic Networks ◽  
Dense Seismic Array ◽  
Beamforming Technique

Abstract Seismograms of earthquakes and explosions recorded at local, regional, and teleseismic distances by a small-aperture, dense seismic array located on Pinyon Flat, in southern California, reveal large (±15°) backazimuth anomalies. We investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques: the broadband frequency-wavenumber (BBFK) technique, the polarization technique, and the beamforming technique. While each technique provided nearly the same direction as a most likely estimate, the beamforming estimate was associated with the smallest uncertainties. Backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the Anza and Caltech seismic networks and the Preliminary Determination of Epicenters (PDE) Bulletin. These backazimuth anomalies have a simple sinelike dependence on azimuth, with the largest anomalies observed from the southeast and northwest directions. Such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array. A best-fit model of a single interface has a dip and strike of 20° and 315°, respectively, and a velocity contrast of 0.82 km/sec. Application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions, suggesting that this is an upper crustal feature. We confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models.

Sign in / Sign up

Export Citation Format

Share Document