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.

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.

An in‐hole shotgun source for engineering seismic surveys

Geophysics ◽  
1987 ◽  
Vol 52 (7) ◽  
pp. 985-996 ◽  
Author(s):  
S. E. Pullan ◽  
H. A. MacAulay
Keyword(s):  
Ground Surface ◽  
Seismic Source ◽  
Coarse Grained ◽  
Near Surface ◽  
Seismic Surveys ◽  
Fine Grained ◽  
Reflection Seismic ◽  
Weight Drop ◽  
Water Saturated ◽  
Excellent Source

We have conducted several source comparisons involving 12‐gauge and 8‐gauge Buffalo guns, a 7.3 kg sledgehammer, and a 75 kg weight drop. The results are strongly site‐dependent. We found that, when the near‐surface consisted of fine‐grained, water‐saturated sediments, the 12‐gauge Buffalo gun produced up to two orders of magnitude more energy than the conventional hammer across a broad frequency range. Under such conditions the gun produced the greatest improvement in energy between 200 and 400 Hz, where it yielded up to ten times more energy than the 75 kg weight drop. This indicates that the Buffalo gun may be particularly useful as a shallow reflection seismic source. However, at sites where the near‐surface materials were coarse‐grained and the water table was well below the ground surface, the advantages of using an in‐hole shotgun source as opposed to a hammer or weight drop were minimal. Nevertheless, in many areas we believe that the Buffalo gun is an excellent source for engineering seismic surveys. It is lightweight and portable (<5 kg), inexpensive to build (<$100 US), simple to use and maintain, and a good source of high‐frequency energy.

Selected Strong and Weak-Motion Data From the Loma Prieta Earthquake Sequence

1989 ◽  
Vol 60 (4) ◽  
pp. 167-176 ◽  
Author(s):  
S. P. Jarpe ◽  
L. J. Hutchings ◽  
T. F. Hauk ◽  
A. F. Shakal
Keyword(s):  
Seismic Response ◽  
Strong Motion ◽  
Spectral Ratio ◽  
The Other ◽  
Ratio Method ◽  
Spectral Ratios ◽  
Near Surface ◽  
Loma Prieta Earthquake ◽  
Rock Site ◽  
Loma Prieta

Abstract The purpose of this paper is to document the strong- and weak-motion seismic data from the Loma Prieta earthquake and its aftershocks obtained by Lawrence Livermore National Laboratory (LLNL), and to present some analysis of the spectral seismic response using both weak- and strong-motion recordings. LLNL operates six free-field, digitally recorded, triaxial, strongmotion accelerographs in the vicinity of LLNL; five of these were operating during the Loma Prieta earthquake. Two days after the main event, LLNL initiated a field deployment of 3-component weak-motion instruments to record aftershocks at three LLNL sites and four California Strong Motion Instrumentation Program (CSMIP) sites that recorded strong-motion from the main event. Spectral ratios of strong- and weak-motion recordings are computed for two pairs of rock and soil sites. One pair of stations is in the vicinity of LLNL, and the other pair is Treasure Island TRI (fill) and Yerba Buena Island YBI (rock) in San Francisco Bay near the Bay Bridge. For the first pair, the weak-motion spectral ratios predict the strong-motion amplification, within 95% confidence limits, for frequencies from 3 to 12 Hz. For TRI and YBI, the strong-motion spectral ratio is much lower than the weak-motion 95% confidence region for frequencies from 1 to 7 Hz. The strong-motion ratio, however, still suggests that the soil underlying TRI resulted in a factor of 3 amplification of energy between 1 and 4 Hz. This is in contrast to the factor of 8 amplification of the weak-motion energy, derived from the spectral ratios of 7 Loma Prieta aftershocks. The large difference between the weak-motion and strong-motion spectral ratios reinforces the limitation that weak-motion cannot be used to directly predict strong-motion amplification at sites underlain by soils that may respond non-linearly at high strain levels. A further examination of weak-motion recordings indicates that the source effect can be removed and the propagation path effects approximated so that the site response can be isolated. Resulting site specific spectral amplifications reveal that the spectral ratio method can lead to erroneous conclusions if the “rock” site has a complicated geology. At two sites near LLNL the apparent diminishing of spectral amplitudes below 5 Hz observed in the spectral ratios was actually due to amplification of spectral response at the rock site. It appears that the reference site spectral ratios at low frequencies may have been influenced by topography or near-surface geologic features. For the other pair of sites, the spectrum at YBI, the rock site, was flat, so that the features in the spectral ratios are due to the seismic response of the soil at TRI.

Two-parameter scaling of source spectra: Love waves from deep-focus Bonin Islands earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 285-300
Author(s):  
R. James Brown
Keyword(s):  
Body Wave ◽  
Scaling Law ◽  
Spectral Ratio ◽  
Love Waves ◽  
Corner Frequency ◽  
Spectral Ratios ◽  
Bonin Islands ◽  
Deep Focus ◽  
Two Parameter ◽  
Fault Length

Abstract Starting with the one-parameter scaling law of Aki, a two-parameter expression is developed to model the source factor of the far-field spectrum from a dislocation fault source for both ω−2 and ω−3 high-frequency asymptotic types. Aki's assumption of similarity is relaxed in two respects: it is neither here assumed that wD0 ∞ L2 (L = fault length, w = fault width, D0 = average dislocation) nor that kT = v kL (kT−1 = correlation time, kL−1 = correlation length, v = velocity of rupture propagation), the latter being equivalent to allowing for Brune's fractional stress drop. From this two-parameter model a four-parameter model of spectral ratio is obtained and fitted to observed spectral ratios by computer optimization of the four parameters. Observed spectral ratios have been determined from the Love waves recorded at NORSAR from six deep-focus Bonin Islands earthquakes using a common-path method. From the optimal values of the four parameters, values are determined for corner frequency (f ≈ 0.2 Hz for m 6.0; f ≈ 0.3 Hz for m = 5.3; m = PDE body-wave magnitude), relative fault length, relative seismic moment (and magnitudes), and p, the slope of the corner-frequency locus. Values found for p are all greater than 3 and such p, in combination with an ω−3 scaling law, can yield a reasonable m:M relation, i.e., with no ceiling imposed on m. A slightly better fit is obtained by starting with an ω−3 model than with ω−2.

Focal mechanism and source depth of earthquakes from body- and surface-wave data

1971 ◽  
Vol 61 (5) ◽  
pp. 1369-1379 ◽  
Author(s):  
Nezihi Canitez ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Source Parameters ◽  
Focal Depth ◽  
Spectral Ratio ◽  
The Body ◽  
Spectral Ratios ◽  
Motion Data ◽  
Wave Data ◽  
Surface Wave Data

abstract The determination of focal depth and other source parameters by the use of first-motion data and surface-wave spectra is investigated. It is shown that the spectral ratio of Love to Rayleigh waves (L/R) is sensitive to all source parameters. The azimuthal variation of the L/R spectral ratios can be used to check the fault-plane solution as well as for focal depth determinations. Medium response, attenuation, and source finiteness seriously affect the absolute spectra and introduce uncertainty into the focal depth determinations. These effects are nearly canceled out when L/R amplitude ratios are used. Thus, the preferred procedure for source mechanism studies of shallow earthquakes is to use jointly the body-wave data, absolute spectra of surface waves, and the Love/Rayleigh spectral ratios. With this procedure, focal depths can be determined to an accuracy of a few kilometers.

scholarly journals Nanoscale Pore Structure Characterization and Permeability of Mudrocks and Fine-Grained Sandstones in Coal Reservoirs by Scanning Electron Microscopy, Mercury Intrusion Porosimetry, and Low-Field Nuclear Magnetic Resonance

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-20 ◽  
Author(s):  
Na Zhang ◽  
Fangfang Zhao ◽  
Pingye Guo ◽  
Jiabin Li ◽  
Weili Gong ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Pore Size ◽  
Mercury Intrusion Porosimetry ◽  
Mercury Intrusion ◽  
Rock Samples ◽  
Fine Grained ◽  
Low Field ◽  
Water Saturated ◽  
Pore Types ◽  
Scanning Electron

Porosity and permeability of two typical sedimentary rocks in coal bearing strata of underground coal mines in China, i.e., mudrocks and fine-grained sandstones, were comprehensively investigated by multiple experimental methods. Measured porosity averages of the helium gas porosity (φg), MIP porosity (φMIP), water porosity (φw), and NMR porosity (φNMR) of the twelve investigated rock samples range from 1.78 to 16.50% and the measured gas permeabilities (Kg) range from 0.0003 to 2.4133 mD. Meanwhile, pore types, pore morphologies, and pore size distributions (PSD) were determined by focused ion beam scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and low-field nuclear magnetic resonance (NMR). FIB-SEM image analyses showed that the mineral matrix pores including interparticle (interP) and intraparticle (intraP) pores with varied morphologies are the dominant pore types of the investigated rock samples while very few organic matter (OM) pores were observed. Results of the MIP and the full water-saturated NMR measurements showed that the PSD curves of the mudrock samples mostly present a unimodal pattern and nanopores with pore diameter less than 0.1 μm are their predominant pore type, while the PSD curves of the fine-grained sandstone samples are featured by a bimodal distribution. Furthermore, comparison of the full water-saturated and irreducible-water-saturated NMR measurements indicated that pores in the mudrocks are solely adsorption pores (normally pore size < 0.1 μm) whereas apart from a fraction of adsorption pores, a large part of the pores in the sandstone sample with relatively high porosity are seepage pores (normally pore size > 0.1 μm). Moreover, the PSD curves of NMR quantitatively converted from the NMR T2 spectra by T2Pc and weighted arithmetic mean (WAM) methods are in good agreement with the PSD curves of MIP. Finally, the applicability of three classic permeability estimation models based on MIP and NMR data to the investigated rock samples was evaluated.

scholarly journals A new type of slumping-induced soft-sediment deformation structure: the envelope structure

Geologos ◽  
2019 ◽  
Vol 25 (2) ◽  
pp. 111-124
Author(s):  
Uk Hwan Byun ◽  
A.J. Tom van Loon ◽  
Yi Kyun Kwon ◽  
Kyoungtae Ko
Keyword(s):  
Slope Failure ◽  
Gravity Flow ◽  
Soft Sediment ◽  
Deformation Structure ◽  
Rare Type ◽  
Fine Grained ◽  
Sediment Deformation ◽  
Soft Sediment Deformation ◽  
The Difference ◽  
Siliciclastic Rocks

Abstract The sediments of the Cretaceous Gyeokpori Formation in south-western South Korea accumulated in a lake in which mainly siliciclastic rocks were deposited, with some interbedded volcaniclastics. The nearby volcanic activity resulted in unstable lake margins inducing a dominance of gravity-flow deposits. The high sedimentation rate facilitated soft-sediment deformation on the sloping margin. The deposition of numerous gravity-flow deposits resulted in a vertically heterolithic stratification. The slumps are composed of different lithologies, which is expressed in different types of deformation due to the difference in cohesion between sandy and mussy layers within the slumps. Coarser-grained (cohesionless) slumps tend to show more chaotic deformation of their lamination or layering. The difference in slumping behaviour of the cohesive and non-cohesive examples is explained and modelled. A unique soft-sediment deformation structure is recognized. This structure has not been described before, and we call it ‘envelope structure’. It consists of a conglomerate mass that has become entirely embedded in fine-grained sediment because slope failure took place and the fine-grained material slumped down with the conglomerate ‘at its back’. The cohesive laminated mudstone formed locally slump folds that embedded the non-cohesive overlying conglomerate unit, possibly partly due to the bulldozing effect of the latter. This structure presumably can develop when the density contrast with the underlying and overlying deposits is exceptionally high. The envelope structure should be regarded as a special – and rare – type of a slumping-induced deformation structure.

Feasibility of the use of Microtremors in Estimating Site Response during Earthquakes: Some Test Cases in Italy

1991 ◽  
Vol 7 (4) ◽  
pp. 551-561 ◽  
Author(s):  
Antonio Rovelli ◽  
Shri K. Singh ◽  
Luca Malagnini ◽  
Alessandro Amato ◽  
Massimo Cocco
Keyword(s):  
Ground Motion ◽  
Seismic Waves ◽  
Site Response ◽  
Spectral Ratio ◽  
Test Cases ◽  
Spectral Ratios ◽  
Cultural Noise ◽  
Maximum Amplification

We explore the feasibility of the use of microtremors in estimating the amplification of seismic waves at soft sites in Italy. Microtremors were measured at three soft sites and nearby hard sites at night when the cultural noise was minimum. These soft sites were selected as those showing the largest amplifications of ground motion during earthquakes as compared to the records on the hard sites or with respect to the predicted spectra. We compare the soft-to-hard site microtremor spectral ratios with the corresponding acceleration spectral ratios. A rough estimate of the shape and level of spectral amplification is obtained from the microtremor data in all three cases. However, the details of the soft-to-hard site spectral ratio are not reproduced and some differences appear in (a) the frequency at which the maximum amplification occurs, and (b) the bandwidth of the significant amplification. More testing of the method is needed before its wider use for microzonation in Italy can be recommended.

Dinosaur trackways from the Upper Cretaceous Oldman and Dinosaur Park formations (Belly River Group) of southern Alberta, Canada, reveal novel ichnofossil preservation style

2015 ◽  
Vol 52 (8) ◽  
pp. 630-641 ◽  
Author(s):  
François Therrien ◽  
Darla K. Zelenitsky ◽  
Annie Quinney ◽  
Kohei Tanaka
Keyword(s):  
Natural Area ◽  
Geochemical Composition ◽  
Fine Grained ◽  
Depositional Settings ◽  
Internal Structures ◽  
Southern Alberta ◽  
Dinosaur Tracks ◽  
Geochemical Analyses ◽  
Water Saturated ◽  
Mineralogical Compositions

Dinosaur tracksites recently discovered in exposures of the Belly River Group in the Milk River Natural Area (MRNA) and Dinosaur Provincial Park (DPP) of southern Alberta represent a novel type of ichnofossils. The tracks, all referable to hadrosaurs, occur as sideritic or calcareous concretions protruding above fine-grained deposits and are here termed concretionary tracks. Detailed sedimentological, petrographic, and geochemical analyses reveal that, although the MRNA and DPP tracks are of different mineralogical compositions (calcium carbonate versus siderite, respectively), they display similar internal structures (microscopic convoluted laminations) and occur in depositional settings indicative of wet paleoenvironments, where the ground was soft and water saturated. These characteristics suggest that concretionary tracks are footprint casts that formed as groundwater rich in dissolved carbonates flooded depressions left in the soft substrate. As the ponded water evaporated, minerals began to precipitate and mix with clastic material transported into the depressions, settling as finely laminated mud within the tracks and filling them either completely or partially. The geochemical composition of the precipitate would depend on the prevalent groundwater conditions (e.g., pH, dissolved carbonate and sulphate concrentrations). Cementation of the tracks occurred relatively soon after burial (<100 years), possibly in response to microbial activity and saturation by mineral-rich groundwater, and modern erosion exposed the concretionary tracks by removing the softer host unit. Recognition of this novel type of ichnofossils suggests dinosaur tracks may be more common than previously thought. Unfortunately, concretionary tracks tend to break apart rapidly when the encasing and underlying substrate erodes away, altering their diagnostic shape and rendering them indistinguishable from nonichnogenic concretions. As such, concretionary tracks may be transient ichnofossils in the badlands, explaining why they are rarely recognized.

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