Evaluation of the relation between near-surface geological units and ground response in the vicinity of Long Beach, California

1979 ◽  
Vol 69 (5) ◽  
pp. 1603-1622
Author(s):  
A. M. Rogers ◽  
J. C. Tinsley ◽  
W. W. Hays ◽  
K. W. King
Keyword(s):  
Strong Motion ◽  
Test Site ◽  
Peak Ground Velocity ◽  
Long Beach ◽  
Spectral Ratios ◽  
Low Velocity ◽  
Ground Response ◽  
Near Surface ◽  
Long Period ◽  
Short Period

abstract Simulataneous recordings of Nevada Test Site nuclear events were made at sites underlain by alluvium in the Long Beach, California, area and at sites underlain by rock in the Palos Verdes and Pasadena areas. These data show peak-ground-velocity alluvium-to-rock ratios as large as 7 and spectral ratios as high as 11 in the period band from 0.2 to 6 sec. Comparison of the low-strain nuclear-explosion data and the San Fernando earthquake strong-motion data at three sites indicates that the alluvium-to-rock spectral ratios derived from the nuclear explosions are similar to those derived from the earthquake. Significant trends exist in the short-period data, indicating higher ground response at sites underlain at the near-surface by materials that have high void ratios and lower ground response with increasing thickness of Quaternary deposits. These results suggest that the short-period response is primarily controlled both by near-surface low-velocity layers and by attenuation in the Quaternary sediments. Comparison of the data of this study with data collected in other areas indicates that the long-period response increase with either increasing depth to basement or with alluvium thickness, when this thickness is greater than 400 m. From previous theoretical studies and these results, ground response in the long-period band is related to those underlying geological structures and major velocity contrasts that control the development of surface waves.

Continuous measurements of microtremors on sediments and basement in Los Angeles, California

1993 ◽  
Vol 83 (5) ◽  
pp. 1595-1609 ◽  
Author(s):  
Hiroaki Yamanaka ◽  
Marijan Dravinski ◽  
Hiroshi Kagami
Keyword(s):  
Los Angeles ◽  
Continuous Measurement ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Earthquake Ground Motion ◽  
Spectral Amplitude ◽  
Spectral Ratios ◽  
Long Period ◽  
Short Period ◽  
Deep Sediments

Abstract Continuous measurement of microtremors at two sites on basement rock and sediments was carried out in Los Angeles, California, in order to understand the fundamental characteristics of microtremors. A predominant peak with a period of about 6.5 sec was found in the microtremor spectra in both media. The spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites. Their time-variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of Los Angeles. This suggests that they originate from an oceanic disturbance. On the other hand, a clear daily variation of spectral amplitudes at a period of 0.3 sec indicates that short-period microtremors are caused by cultural noises. It was found that the spectral ratio of long-period microtremors between the basement and the sediments was repeatable, although the spectral amplitudes at the two sites were time-variant. The spectral ratio of the long-period microtremors was similar to that derived from strong motion records. This suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long-period earthquake ground motion.

P–Coda Evidence for a Layer of Anomalous Velocity in the Crust Beneath Leduc, Alberta

1972 ◽  
Vol 9 (7) ◽  
pp. 845-856 ◽  
Author(s):  
P. G. Somerville ◽  
R. M. Ellis
Keyword(s):  
Synthetic Seismograms ◽  
Precambrian Basement ◽  
Upper Crust ◽  
Spectral Ratios ◽  
Low Velocity ◽  
Crustal Model ◽  
Short Period ◽  
Large Velocity ◽  
Theoretical Results ◽  
Velocity Zone

Previous seismic studies of crustal structure using short-period P-coda recorded in the vicinity of Leduc in central Alberta have indicated that serious discrepancies exist between the experimental observations and those based on a horizontally layered model of the crust in both the time and frequency domains.Using vertical-radial spectral ratios and synthetic seismograms, a modified crustal model has been derived which gives better agreement between experimental and theoretical results. This model involves the insertion of a layer several kilometers thick having large velocity contrast with respect to the surrounding media at the base of the Precambrian basement (12 km deep). The new crustal model is discussed in the light of evidence for a low velocity zone in the upper crust in certain continental regions.

scholarly journals Frequency dependent amplification of weak ground motions in Porirua and Lower Hutt, New Zealand

1992 ◽  
Vol 25 (4) ◽  
pp. 303-331 ◽  
Author(s):  
J. John Taber ◽  
Euan G. C. Smith
Keyword(s):  
New Zealand ◽  
Frequency Band ◽  
Spectral Ratio ◽  
Silty Sand ◽  
Peak Ground Velocity ◽  
Soft Sediment ◽  
Spectral Ratios ◽  
Near Surface ◽  
Fine Grained ◽  
Water Saturated

The relative ground response due to microearthquakes has been examined at a total of 36 sites in the Porirua and Lower Hutt regions of New Zealand, as part of a multi-disciplinary microzoning project conducted with the Wellington Regional Council. The sites were studied in two separate experiments and were chosen to sample a variety of soil types and depths ranging from strong rock to thick sections of alluvial gravels and sands to soft water-saturated fine-grained deposits. The amplitude response of each site relative to a bedrock reference site has been determined as a function of frequency. Fourier spectral ratios (Fsr) were calculated for each earthquake and then between three and twenty-six earthquakes were averaged together at each of the sites. Spectral ratios of individual earthquakes varied significantly from the average spectral ratio. In the Hutt Valley there is a gradual down-valley increase in shaking in a similar pattern to the down-valley increase of the depth to bedrock and thickness of near-surface soft sediment. The response at the upper-most valley sites, underlain by less than 50 m of alluvial gravel and silty sand, is similar to the response at the rock sites on the side of the valley (Fsr = 2.4) while the Fourier spectral ratios reach 14 at the lower-most valley sites, which are underlain by greater than 20 m of soft sediment. The highest amplifications were recorded at two sites on soft flexible sediments (10 to 35 m thick) in an enclosed valley (Fsr = 16 to 18) and a site on an apparently drained and filled swamp (Fsr = 15). A spectral ratio of 18 corresponds to an increase in peak ground velocity by a factor of 5. The amplification at most Lower Hutt sites occurred over a broad frequency band from 0.5 Hz to up to 5 Hz, with the high frequency limit of the band decreasing as the spectral ratio in the band increased. Two of the flexible sediment sites exhibited a very narrow frequency response with a peak in the 1-2 Hz range, similar to three flexible sediment sites in the Porirua basin where the amplification was in the 1-3 Hz frequency band. These flexible sediment sites had Fourier spectral ratios of up to 18 relative to a hard rock site. Three other Porirua sites had spectral ratios greater than 5 at some frequency. Two of these sites were on fan alluvium and fine grained sediment, while the third was on siltly sand on a topographic ridge. The remaining five sites were on weathered gravels and showed little amplification.

scholarly journals The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

1978 ◽  
Vol 68 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Near Field ◽  
Dislocation Line ◽  
Strong Motion ◽  
Body Waves ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Wave Forms ◽  
San Fernando ◽  
The Time Domain

abstract Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 1026 dyne-cm. Implications for near-field modeling are drawn from these results.

Observational Test for Wave Propagation Effects in Local Earthquake Seismograms

1990 ◽  
Vol 61 (2) ◽  
pp. 109-116 ◽  
Author(s):  
David E. Williams ◽  
Charles A. Langston
Keyword(s):  
Thin Layer ◽  
Three Dimensional ◽  
Strong Motion ◽  
Careful Analysis ◽  
Corner Frequency ◽  
Vector Particle ◽  
Low Velocity ◽  
Waveform Data ◽  
Near Surface ◽  
Source Models

Abstract Strong motion data for aftershocks of the 1982 Miramichi earthquake are analyzed to determine site effects on recorded waveforms. Although aftershocks vary in source mechanism, the complicated vector particle motion of P and S arrivals are often coherent between events recorded at the same station. This suggests that near-surface receiver structure has a significant effect on the recorded waveforms. Resonance features dominate the wavetrains with P reverberations existing on the vertical components and S reverberations prominent on the radial components indicating near vertical incidence. These reverberations take the form of peaks in the amplitude spectra which may complicate corner frequency interpretation. As an example, a corner frequency shift, fc(S) < fc(P), is evident and is attributed to structure induced effects. Synthetic seismograms computed using the propagator matrix method indicate that a thin low velocity layer of unconsolidated glacial till located directly beneath the receivers is responsible for most waveform effects. Attenuation effects in the thin layer are included in the computation of the synthetics in order to help match amplitude ratios. The geometry of the till-bedrock interface is interpreted as being three dimensional due to high tangential P amplitudes and anomalous particle motions. The observed waveforms are believed to consist mainly of direct waves, reverberations within the thin layer, and scattered arrivals resulting from the nonplanar interface. A careful analysis of three component waveform data in earthquake aftershock data sets such as this one considered here may be useful in determining local site conditions independent of assumed source models.

scholarly journals On the Utility of Horizontal-to-Vertical Spectral Ratios of Ambient Noise in Joint Inversion with Rayleigh Wave Dispersion Curves for the Large-N Maupasacq Experiment

Sensors ◽  
2021 ◽  
Vol 21 (17) ◽  
pp. 5946
Author(s):  
Maik Neukirch ◽  
Antonio García-Jerez ◽  
Antonio Villaseñor ◽  
Francisco Luzón ◽  
Jacques Brives ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Joint Inversion ◽  
Dispersion Curves ◽  
P Wave ◽  
Gravity Inversion ◽  
Spectral Ratios ◽  
Near Surface ◽  
Dispersion Data ◽  
Short Period

Horizontal-to-Vertical Spectral Ratios (HVSR) and Rayleigh group velocity dispersion curves (DC) can be used to estimate the shallow S-wave velocity (VS) structure. Knowing the VS structure is important for geophysical data interpretation either in order to better constrain data inversions for P-wave velocity (VP) structures such as travel time tomography or full waveform inversions or to directly study the VS structure for geo-engineering purposes (e.g., ground motion prediction). The joint inversion of HVSR and dispersion data for 1D VS structure allows characterising the uppermost crust and near surface, where the HVSR data (0.03 to 10s) are most sensitive while the dispersion data (1 to 30s) constrain the deeper model which would, otherwise, add complexity to the HVSR data inversion and adversely affect its convergence. During a large-scale experiment, 197 three-component short-period stations, 41 broad band instruments and 190 geophones were continuously operated for 6 months (April to October 2017) covering an area of approximately 1500km2 with a site spacing of approximately 1 to 3km. Joint inversion of HVSR and DC allowed estimating VS and, to some extent density, down to depths of around 1000m. Broadband and short period instruments performed statistically better than geophone nodes due to the latter’s gap in sensitivity between HVSR and DC. It may be possible to use HVSR data in a joint inversion with DC, increasing resolution for the shallower layers and/or alleviating the absence of short period DC data, which may be harder to obtain. By including HVSR to DC inversions, confidence improvements of two to three times for layers above 300m were achieved. Furthermore, HVSR/DC joint inversion may be useful to generate initial models for 3D tomographic inversions in large scale deployments. Lastly, the joint inversion of HVSR and DC data can be sensitive to density but this sensitivity is situational and depends strongly on the other inversion parameters, namely VS and VP. Density estimates from a HVSR/DC joint inversion should be treated with care, while some subsurface structures may be sensitive, others are clearly not. Inclusion of gravity inversion to HVSR/DC joint inversion may be possible and prove useful.

Observation of 1- to 5-second microtremors and their application to earthquake engineering. Part I: Comparison with long-period accelerations at the Tokachi-oki earthquake of 1968

1978 ◽  
Vol 68 (3) ◽  
pp. 767-779
Author(s):  
Yutaka Ohta ◽  
Hiroshi Kagami ◽  
Noritoshi Goto ◽  
Kazuyoshi Kudo
Keyword(s):  
Earthquake Engineering ◽  
Underground Structure ◽  
Strong Motion ◽  
Period Range ◽  
Predominant Period ◽  
High Rise ◽  
Long Period ◽  
Short Period ◽  
Source And Path Effects ◽  
Observation Line

abstract A study on elucidation of possible amplification characteristic of strong motions due to deep situated deposit was made by means of 1 to 5 sec microtremors observation. At the Tokachi-oki earthquake of 1968 (M=7.9) several accelerograms were obtained, among which some are dominant but others are not significant in longer periods than 1 sec. To understand whether these differences are from source and path effects or site conditions is important for estimating seismic input motions to high-rise buildings. A long-period microtremors observation was introduced to pursue this problem. Observations were carried out in three cities where the typical acceleration records had been obtained, employing a specially designed instrument good for the microtremors with periods ranging from 0.5 to 6 sec. Each observation line was chosen so as to traverse the accelerograph site along which a remarkable geological change of the underground structure is expected, for example, from the outcrop of bedrock to the alluvial deposit. Through comparison of the obtained spectra and their peaks with those derived from the strong-motion records, it was derived that their predominancy and predominant period in the long-period range are clearly responsible to the presence of deep situated deposit. A formulation of observation and analysing procedures of the long-period microtremors was also proposed, paying attention to overcome the defects in the well-known technique for the short-period microtremors.

scholarly journals Parkfield earthquake of June 28, 1966: Magnitude and source mechanism

1968 ◽  
Vol 58 (2) ◽  
pp. 689-709
Author(s):  
Francis T. Wu
Keyword(s):  
Love Wave ◽  
Main Shock ◽  
Near Field ◽  
Strong Motion ◽  
Wave Radiation ◽  
Motion Data ◽  
Long Period ◽  
Short Period ◽  
Double Couple ◽  
Parkfield Earthquake

Abstract The Parkfield earthquake of June 28, 1966 (04:26:12.4 GMT) is studied using short-period and long-period teleseismic records. It is found that (1) Mb = 5.8 and Ms = 6.4 as compared to Mb = 5.4 and Ms = 5.4 for the foreshock (04:08:54), (2) both the Rayleigh and Love wave radiation patterns conform to those of a double couple at a depth of about 8.6 km, (3) the main shock can be represented by a series of shocks separated in space and time. The near-field strong-motion data support the last conclusion. Based on strong-motion seismograms, and the surficial evidences of the dimensions of the fault, the energy is found to be 1021 ergs.

High-frequency Rayleigh-wave tomography using traffic noise from Long Beach, California

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. B43-B53 ◽  
Author(s):  
Jason P. Chang ◽  
Sjoerd A. L. de Ridder ◽  
Biondo L. Biondi
Keyword(s):  
Traffic Noise ◽  
Long Beach ◽  
Low Velocity ◽  
Near Surface ◽  
Linear Feature ◽  
The North ◽  
Local Roads ◽  
Geologic Map ◽  
Wave Tomography ◽  
Dense Seismic Array

Using a dense seismic array in Long Beach, California, we have investigated the effectiveness of using traffic noise for passive subsurface imaging. Spectral analysis revealed that traffic-induced vibrations dominate the ambient seismic noise field at frequencies between 3 and 15 Hz. Using the ambient-noise crosscorrelation technique at these frequencies, we have extracted fundamental- and first-order-mode Rayleigh waves generated by Interstate 405 and local roads. We picked group traveltimes associated with the fundamental mode and used them in a straight-ray tomography procedure to produce group velocity maps at 3.0 and 3.5 Hz. The velocity trends in our results corresponded to shallow depths and coincided well with lithologies outlined in a geologic map of the survey area. The most prominent features resolved in our velocity maps were the low velocities to the north corresponding to less-consolidated materials, high velocities to the south corresponding to more-consolidated materials, a low-velocity zone corresponding to artificial fill in Alamitos Bay, and a low-velocity linear feature in the Newport-Inglewood Fault Zone. Our resulting near-surface velocities can be useful for identifying regions that are susceptible to serious damage during earthquake-related shaking.

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