ReMi Technique Research Articles

Seismic site effects in Setúbal county (Portugal) using remi technique

Setúbal is a county located in the Lisbon metropolitan area (Portugal) which has been hit by historical earthquakes that were responsible for high social and economic losses. The 1858 earthquake, with an epicentre located offshore just south of the Setúbal region, is a good example of an earthquake that caused high damage (IX-VIII MM) in this county. The main city of the region is Setúbal itself, an important and populated urban agglomeration with several industrial facilities very close by. The old city centre is mostly settled upon shallow geological units and taking into consideration the historical seismicity, it is important to examine the possible site effects that could occur during future earthquakes affecting the Setúbal region.The objectives of this study are therefore the characterisation of the seismic behaviour of Setubal's shallow geological formations and the evaluation of potential site effects. Shear wave velocity profiles were computed with the Refraction Microtremor (ReMi) method, spatial distribution of VS30 values was estimated and a map with the VS30 classification of soils according to the EC8 was produced. Spatial distributions of different data are presented and discussed: VS30 values, thickness of the shallow formations, top Pliocene surface, and results from Standard Penetration Tests (NSPT values). Numerical correlations between these parameters were established. Geotechnical characterisation was based on the analysis of 307 logs and 2950 Standard Penetration Tests. A total of 266 refraction microtremor measurements were performed obtaining VS profiles and VS30 values for 43 different sites. It was found that in Setúbal the majority of the Holocene units belong to EC8 class C (180–360 m/s) but, in the areas where the thickness of shallow formations (TSF) is lower, the Holocene units may belong to class B (> 360 m/s). The spatial distribution of VS30 highlighted that the Plio-Pleistocene, Miocene and Mesozoic areas show the best soil conditions corresponding to EC8 classes B and A. However, it was possible to identify a Plio-Pleistocene area with VS30 varying between 232 and 355 m/s, therefore belonging to class C. This fact highlights that site effects studies should not be performed solely based on geological criteria, but it is essential to estimate S wave velocities (VS) in situ.

Multidisciplinary site investigations: refraction microtremor surveys

We present three case studies from recent site investigations that have utilised geophysical data to supplement traditional geotechnical investigations. The refraction microtremor (ReMi) method, which measures the shear-wave velocity of the subsurface soil profile, is used to enhance our overall understanding of geotechnical site conditions. Interpolation of the closely spaced one-dimensional velocity-depth profiles along linear arrays allows two- or three-dimensional velocity-versus-depth representations to be produced, thereby mapping lateral variations and extending subsurface characterisations between more expensive spot borehole measurements. The ReMi technique provides a non-invasive and cost-effective way of estimating vertical soil/rock shear-wave versus depth profiles and therefore is an effective reconnaissance tool for targeting key areas for further, more expensive intrusive investigation method. This paper examines the contribution ReMi shear-wave velocity assessments can make towards enhancing subsurface geological and geotechnical models to mitigate risk from unforeseen ground conditions. Case studies demonstrate the benefits of incorporating the shear-wave velocity estimates from ReMi into the geotechnical investigations. These include identifying the thickness of basalt flows, identifying the location of buried stream channels, characterising palaeo-topographical features, identifying areas of low velocity which may be prone to liquefaction, and assessing the thickness and velocity variations within geological units between borehole and test pit locations. The objective is not to replace traditional geotechnical investigations but allow more meaningful ground models to be developed.

Empirical correlation of shear wave velocity (vs) with spt of soils in Madrid

Empirical correlations are usually used as a predictive tool in geotechnical engineering. However, equations calculated for soils very different to the ones to be characterized are frequently used, and so they are not representative of their mechanical properties. This fact, added to the increasing interest of civil engineering in knowing the shear wave velocity (Vs) of the ground, has led to the calculation of different empirical equations to predict the Vs value of the soils of Madrid. In this study this has been achieved by calculating the empirical correlations between the Vs value obtained through the ReMi (Refraction Microtremor) technique and the Standard Penetration Test (500 NSPT values). The empirical correlations proposed are applicable to the whole metropolitan area of Madrid, and have an excellent predictive capability owing to the incorporation of the measurement depth to the equations, which has an important influence in the resistance properties of soils. It is always better to have data collected in the studied site. But often there are too many difficulties to carry out some of these surveys. It may also happen that the surveys take too long or are too expensive to carry out. In these situations, empiric equations can be used to estimate this data. In geotechnical engineering, these empiric correlations are used frequently as a predictive tool, especially in the project’s design primary phases, when vast extensions of terrain are to be characterized in a short period of time, and to define if the soil fits a specific purpose. Because of this factor, there are plenty of estimations published that link between them different types of mechanical properties and geotechnical parameters.

Comparisons betweenVS30and Spectral Response for 30 Sites in Newcastle, Australia, from Collocated Seismic Cone Penetrometer, Active‐ and Passive‐SourceVSData

Although the time‐averaged shear‐wave velocity down to 30 m depth ( V S 30) can be a proxy for estimating earthquake ground‐motion amplification, significant controversy exists about its limitations when used as a single parameter for the prediction of amplification. To examine this question in absence of relevant strong‐motion records, we use a range of different methods to measure the shear‐wave velocity profiles and the resulting theoretical site amplification factors (AFs) for 30 sites in the Newcastle area, Australia, in a series of blind comparison studies. The multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface‐wave data, with newly acquired horizontal‐to‐vertical spectral ratio, passive‐source surface‐wave spatial autocorrelation (SPAC), refraction microtremor (ReMi), and multichannel analysis of surface‐wave data. The various measurement techniques predicted a range of different AFs. The SPAC and ReMi techniques have the smallest overall deviation from the median AF for the majority of sites. We show that V S 30 can be related to spectral response above a period T of 0.5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear‐wave velocity profiles. Both V S 30 and AF values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low‐velocity layers ( 0.5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes.

Double-array refraction microtremors

We present a critical analysis of the limitations of the standard ReMi technique, specifically in the case of directional sources, and we propose an alternative approach for the efficient acquisition and processing of passive surface wave data, that exploits a simple and yet effective field layout (two linear orthogonal arrays) and processing strategy. The motivations for using a 2D array for passive surface wave testing are reviewed, together with the limitations of the classical ReMi approach. Using synthetic and real data, the robustness of the method is shown, and the limitations of the simplified processing route are described. The possibility of acquiring active data on the same receiver spread allows a partial validation of the passive results, in terms of propagation direction, in addition to producing a broader band dispersion curve to be used in the inversion process. The proposed approach is an intermediate step towards the full complexity of beamforming analysis, that can be of simple use for practitioners and yet help avoid the most common and dangerous interpretation pitfalls inherent to linear array micro-tremor techniques.

Average shear wave velocity of the plain of the province of Treviso (Northern Italy)

The accompanying map is the result of a regional survey to present average shear wave velocity in the uppermost layers (20–40 m in depth) of a large area situated in the province of Treviso, northeastern Italy. The research was conducted using the Refraction Microtremors (ReMi) seismic technique. Data from a total of 250 recording stations, scattered over an area of 2000 km2, was collected during a two months in early 2006. The final Vs map shows the tight correlation between the seismic response of the area and the structure of alluvial deposits formed during late Pleistocene and Holocene. The ReMi technique, as well as the other techniques based on the survey of the surface wave, can be valuable tools for regional mapping average values of the shear wave in near surface deposits. These data, from a seismological perspective, along with measurements of the fundamental period, represent an excellent alternative for the site modeling.

Validity of the Refraction Microtremors (ReMi) Method for Determining Shear Wave Velocities for Different Soil Types in Egypt

The Refraction Microtremor (ReMi) method is being used around the world by the geotechnical and geophysical community to determine shear-wave velocities. This is due to its faster, less expensive and accurate determination of shear wave velocities, when compared to other methods used. Unlike standard crosshole and downhole techniques, ReMi does not require any drilling. It eliminates the problem of shear-wave source and quiet site that are pre-requisites for good seismic refraction surveys. In this paper we present refraction microtremors (ReMi) measurements done at sites underlain by different soil types in Egypt. The ReMi data were collected using standard refraction equipment employing 12, 24 or 48 channels. We used deep oceanographic noise and ambient noise including energy from power generators, pile drivers and traffic. The data were processed using the SeisOpt® ReMi? (© Optim, Inc.) software to reveal one-dimensional shear-wave velocity structures beneath the arrays. To access the validity of the method for the Egyptian soils, the shear-wave profiles obtained from the ReMi measurements were compared to downhole and crosshole data for different soils. Comparisons demonstrate the robustness of the ReMi technique for obtaining shear-wave velocities for different soil types in Egypt.

Comparison among SASW, ReMi and PS-logging techniques: Application to a railway embankment

Results obtained by SASW and PS-logging (in-hole) seismic techniques are compared with the relatively new ReMi (Refraction microtremor) method at a common site with a well-known soil profile: a recently constructed high-speed railway embankment. PS-logging is the most accurate technique in identifying the soil profile of the embankment followed by Re-Mi and SASW. Mean shear wave velocity estimations are also higher for PS-logging, followed by SASW and ReMi, while mean deviation is similar in each technique. The ReMi technique has provided very accurate results in the study of the embankment profile, which in addition to its high operability and its fast data processing, makes it a very convenient technique for extensive geotechnical surveys.

Genetic introduction of foreign genes to Pleurotus eryngii by restriction enzyme-mediated integration

Pleurotus eryngii was transformed via restriction enzyme-mediated integration. In order to construct the transformation plasmid, the enhanced cyan fluorescent protein (ECFP) gene was ligated next to the gpd promoter of the plasmid pAN7-1. Transformation was facilitated via the heat treatment of a transformation mixture containing 1 microg of the HindIII-digested plasmid DNA and 10(6) mushroom protoplasts in 40% polyethyleneglycol solution, resulting in 10-40 hygromycin-resistant transformants. Successful transformation was evidenced by PCR, Southern blot, and confocal fluorescence microscopic analyses on the selected transformants. To date, this is the first report on the transformation of P. eryngii by REMI technique.

Characterization of Near-Surface Geology at Strong-Motion Stations in the Vicinity of Reno, Nevada

Abstract We evaluate site conditions at each of the 21 Advanced National Seismic System (ANSS) strong-motion stations in the Reno–Sparks, Nevada, area. Shallow shear-wave velocities are measured using the refraction microtremor (ReMi) technique (Louie, 2001). Average velocities to depths of 30 and 100 m are compared with local geological and soil classifications. Generalized 1:250,000 scale geological classifications show some variations in unit averages of the measured velocities, but variations between units are much smaller than the standard deviations of velocities within units having multiple measurements. Site velocities are weakly correlated with the weight percent of gravel, sand, silt, and clay in the soil unit at the surface. Predictions of site velocities based on these soil sediment percentages fall within ±20% of measured values for all but two of the 21 sites.

Measurement of shallow shear wave velocities at a rock site using the ReMi technique

Shallow shear wave velocities beneath a rock site are characterized using the refraction microtremor (ReMi) technique developed by Louie [Faster, better: shear-wave velocity to 100 m depth from ReMi arrays. Bull Seism Soc Am 2001; 91: 347–64]. Ground motion from a passing train enabled capture of energy propagating parallel to the recording array. This allowed evaluation of the variation of the minimum phase-velocity of the dispersion curve envelope and better estimation of the true minimum velocity beneath the site. We use a new method to image and evaluate the dispersion curve envelope via power–slowness profiles through the slowness–frequency plots introduced by Louie [Faster, better: shear-wave velocity to 100 m depth from ReMi arrays. Bull Seism Soc Am 2001; 91: 347–64]. Data illustrated the frequency dependency of dispersion curve uncertainties, with greater uncertainty occurring at low frequencies. These uncertainties map directly into uncertainty of the inverted velocity–depth profile. Above 100 m depth velocities are well constrained with 10% variability. Variability is greatly reduced when the energy propagation is along the geophone array. Greater velocity variation is observed below 100 m depth.

Shear Wave Velocity Profiles via Seismic Cone Penetration Test and Refraction Microtremor Techniques at ANSS Strong Motion Sites in Charleston, South Carolina

The Charleston, South Carolina, region is considered to have the highest seismic hazard on the east coast of the United States and has been chosen as a location for an Urban Strong Motion Array of the Advanced National Seismic System (ANSS). This paper will report on subsurface investigations of the shallow shear wave velocity beneath the first four ANSS strong motion stations in Charleston. Both borehole (seismic cone penetration test or SCPT) and surficial seismic (refraction microtremor or ReMi) methods were used to determine shear wave velocities to a depth of 30 m beneath each site. All sites are National Eearthquake Hazards Reduction Program (NEHRP) Class D ( V S30 < 360 m/s), with V S30 ranging from 215 to 344 m/sec. Three sites have low-velocity zones within the shallow sedimentary section. The V S30 derived from the SCPT and ReMi techniques agree within 10% at three sites and within 15% at all four sites.

Transgenic approaches to retinal development and function in Xenopus laevis

The African clawed frog Xenopus laevis has long been used to study the development and function of the vertebrate retina. An efficient technique for generating transgenic Xenopus embryos, the REMI procedure, has enabled the stable overexpression of transgenes in developing and mature X. laevis. In the retina, transgenes driven by retinal-specific promoters have been used to study protein trafficking, circadian rhythms, and retinal degeneration. The REMI technique is surprisingly simple, consisting of integration of plasmid DNA into permeabilized sperm nuclei, followed by transplantation of these nuclei into unfertilized eggs. Here, we describe the reagents and steps necessary for generation of transgenic embryos using the REMI reaction and discuss its applications for the study of retinal development.