scholarly journals Reference stations for Christchurch

2012 ◽  
Vol 45 (4) ◽  
pp. 184-195 ◽  
Author(s):  
C. Van Houtte ◽  
O.-J. Ktenidou ◽  
T. Larkin ◽  
A. Kaiser
Keyword(s):  
Reference Site ◽  
Spectral Ratio ◽  
Site Effect ◽  
Reference Station ◽  
Topographic Effects ◽  
S Wave ◽  
Rock Outcrop ◽  
Soft Soils ◽  
Seismic Stations ◽  
Hvsr Method

During the Canterbury earthquake sequence, the observed level of ground motion on the soft soils of Christchurch was very strong and highly variable. Many studies are now emerging that analyse the amplification effect of these soft soils, usually by estimating a frequency-dependent amplification function relative to a rock outcrop station, or ‘reference site’. If the rock outcrop has its own amplification due to weathering or topographic effects, then the calculated amplification for the soil sites can be compromised. This study examines ten seismic stations in Canterbury to determine the best reference site for Christchurch, using the horizontal-to-vertical spectral ratio (HVSR) method for S-wave shaking. More broadly, this study uses HVSR to expand existing knowledge of the dynamic characteristics of seismic stations in the Canterbury area. Most rock stations show their own local amplification effects that reduce their individual ability to be used as reference stations. The recently installed Huntsbury station (HUNS) appears to be the best reference site for Christchurch, but this will need to be verified when more records become available. In the meantime, the D13C temporary station is currently the best reference station for site effect studies in both Christchurch and Lyttelton.

Site effect evaluation using spectral ratios with only one station

1993 ◽  
Vol 83 (5) ◽  
pp. 1574-1594
Author(s):  
Javier Lermo ◽  
Francisco J. Chávez-García
Keyword(s):  
Transfer Function ◽  
Rayleigh Waves ◽  
Site Effects ◽  
Spectral Ratio ◽  
Site Effect ◽  
Reference Station ◽  
Effect Evaluation ◽  
Spectral Ratios ◽  
S Wave ◽  
Dominant Period

Abstract The spectral ratio technique is a common useful way to estimate empirical transfer function to evaluates site effects in regions of moderate to high seismicity. The purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station. The technique, originally proposed by Nakamura to analyze Rayleigh waves in the microtremor records, is presented briefly and it is discussed why it may be applicable to study the intense S-wave part in earthquake records. Results are presented for three different cities in Mexico: Oaxaca, Oax., Acapulco, Gro., and Mexico City. These cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city. Each time we compare the results of Nakamura's technique with standard spectral ratios. In all three cases the results are very encouraging. We conclude that, if site effects are caused by simple geology, a first estimate of dominant period and local amplification level can be obtained using records of only one station.

scholarly journals The horizontal-to-vertical spectral ratio and its applications

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Rong Xu ◽  
Lanmin Wang
Keyword(s):  
Shear Wave ◽  
Velocity Structure ◽  
Site Response ◽  
Mineral Exploration ◽  
Spectral Ratio ◽  
Site Effect ◽  
Research Area ◽  
Site Classification ◽  
S Wave ◽  
Borehole Data

AbstractThe horizontal-to-vertical spectral ratio (HVSR) has been extensively used in site characterization utilizing recordings from microtremor and earthquake in recent years. This method is proposed based on ground pulsation, and then it has been applied to both S-wave and ambient noise, accordingly, in practical application also different. The main applications of HVSR are site classification, site effect study, mineral exploration, and acquisition of underground average shear-wave velocity structure. In site response estimates, the use of microtremors has been introduced long ago in Japan, while it has long been very controversial in this research area, as there are several studies reporting difficulties in recognizing the source effects from the pure site effects in noise recordings, as well as discrepancies between noise and earthquake recordings. In practice, the most reliable way is the borehole data, and the theoretical site response results were compared with the HVSR using shear wave to describe site response. This paper summarizes the applications of the HVSR method and draws conclusions that HVSR has been well applied in many fields at present, and it is expected to have a wider application in more fields according to its advantages.

Utility of the horizontal-to-vertical spectral ratio passive seismic method for estimating thickness of Quaternary sediments in Minnesota and adjacent parts of Wisconsin

2016 ◽  
Vol 4 (3) ◽  
pp. SH71-SH90 ◽  
Author(s):  
Val W. Chandler ◽  
Richard S. Lively
Keyword(s):  
Cross Sections ◽  
Spectral Ratio ◽  
Sediment Thickness ◽  
S Wave ◽  
Widespread Application ◽  
Near Surface ◽  
Seismic Method ◽  
Calibration Curves ◽  
Passive Seismic ◽  
Hvsr Method

Quaternary glacial and fluvial sediments in Minnesota and adjacent areas are a major source for groundwater, and they are important to many geologic investigations. Unfortunately, the thicknesses of these widespread sediments are often poorly known. The horizontal-to-vertical-spectral ratio (HVSR) passive seismic method is being increasingly used in the region to assist in mapping the thickness of these sediments and the topography of the underlying bedrock surface. HVSR results when control sites with known sediment thickness are used to derive calibration curves that in turn are used to estimate sediment thicknesses in areas lacking control. The HVSR method must be used with appropriate caution. Extreme variations in S-wave velocities of near-surface materials can complicate or even negate the use of calibration curves, and very irregular bedrock surfaces can produce weak, multipeak HVSR spectra that are difficult to interpret. Over soft bedrock, HVSR peaks may reflect intrabedrock features, and velocity contrasts within the glacial sequence can overwhelm HVSR bedrock signatures. Nonetheless, the HVSR method has proven a useful tool to investigate Quaternary geology and depth to bedrock in areas of the state where subsurface data are limited. Thickness estimate errors are usually less than 25%, which is adequate for many geologic applications. The addition of multilocation spectral profiles and cross sections anchored with bedrock control points has allowed us to use data with poor signal quality and to achieve good continuity away from control stations. HVSR methods provide a suitable and cheaper alternative to conventional seismic studies, and they help to target sites for Quaternary drilling programs, bedrock topography evaluation, and determining glacial sediment thickness for 3D mapping. In areas where conventional seismic profiling may be necessary, the HVSR method is useful in selecting and prioritizing targets. The HVSR method should have widespread application in the glaciated areas of the north-central midcontinent.

scholarly journals Seasonal variations in amplitudes and resonance frequencies of the HVSR amplification peaks linked to groundwater

2021 ◽  
Vol 226 (1) ◽  
pp. 1-13
Author(s):  
Alexis Rigo ◽  
Efthimios Sokos ◽  
Valentine Lefils ◽  
Pierre Briole
Keyword(s):  
Soil Moisture ◽  
Wave Velocity ◽  
Maximum Amplitude ◽  
Spectral Ratio ◽  
Vertical Surface ◽  
Sediment Layer ◽  
S Wave ◽  
Surface Displacements ◽  
Resonance Frequencies ◽  
Hvsr Method

SUMMARY Following the installation of a temporary seismological network in western Greece north of the Gulf of Patras, we determined the quality of the sites of each of the 10 stations in the network. For this, we used the horizontal-to-vertical spectral ratio (HVSR) method and calculated an average curve over randomly selected days between 0 and 10 Hz. The daily HVSR curve is determined by the HVSR 12-hr calculation (1 hr every two) without distinction between seismic ambient noise and earthquake signal. The HVSR curves obtained can be classified in three categories: flat curves without amplification, curves with a amplification peaks covering a large frequency range, and curves with one or more narrow peaks. In this third category C3, one station has one peak, two have two and one has three. On the contrary of what it is commonly assumed, the amplitudes and the resonance frequencies of these narrow peaks are not stable over time in C3. We determined the maximum of the amplitude of each peak with the corresponding central frequency for each day during 2.5 yr. Except for the station with three peaks, which finally appears stable within the uncertainties, the principal peak exhibits a seasonal variation, with a maximum in winter and a minimum in summer, the observations being more dispersed during winter. The second peak, when it exists, varies in the same way except at one station where it varies oppositely. These variations are clearly correlated with the loading and unloading cycle of the underlying aquifers as shown by the comparison with water level and yield measurements from wells located close to the stations. Moreover, they are also correlated with the vertical surface displacements observed at continuously recording GPS stations. The dispersion of the observed maximum amplitude in winter is probably related to the rainfall and the soil moisture modifying the S-wave velocity as revealed by other studies. From this study, we would like to emphasize that the use the HVSR method to constrain the S-wave velocity and the thickness of the sediment layer over the bedrock in the basin, has to be done with caution. Upon further confirmation of its robustness, the HVSR methodology presented here could be a good and easy-to-use tool for a qualitative survey of the aquifer backdrop and its seasonal behaviour, and of the soil moisture conditions.

scholarly journals A STUDY OF MICROTREMOR HVSR IN THE RIO-ANTIRIO AREA, (GREECE)

2017 ◽  
Vol 50 (3) ◽  
pp. 1194
Author(s):  
M.E. Norda ◽  
A. Prapiga ◽  
P. Paraskevopoulos ◽  
G.A Tselentis
Keyword(s):  
Fundamental Frequency ◽  
Main Part ◽  
Ambient Noise ◽  
Spectral Ratio ◽  
Recording Time ◽  
Seismic Stations ◽  
Central Greece ◽  
Hvsr Method

Horizontal to Vertical Spectral Ratio (HVSR) method has been applied on ambient noise records at the Rio- Antirio area (central Greece). The dataset used was recorded during 7 days by 12 temporary seismic stations deployed in the area. The stations were laid out along a profile and their interval was approximately 500m. The main part of the processing was done using Geopsy software. The aim of this study was to estimate the fundamental frequency at the station sites and its variation with time and azimuth. The processing results showed that for most stations along the profile, the peaks of the HVSR curve are not strong enough and often there are, more than one, peaks, which seem to be persistent during the whole recording time. When taking the azimuth into account, some of the stations show dominant and persistent directions were the HVSR ratio is stronger, while it has been observed that this direction could vary for different frequency peaks of the same stations. Finally, the top sediment layer’s geometry and thickness were estimated using Vs velocity results from nearby crosshole measurements.

Horizontal-to-Vertical Spectral Ratio (HVSR) IRIS Station Toolbox

2020 ◽  
Vol 91 (6) ◽  
pp. 3539-3549
Author(s):  
Manochehr Bahavar ◽  
Zack J. Spica ◽  
Francisco J. Sánchez-Sesma ◽  
Chad Trabant ◽  
Arash Zandieh ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Spectral Ratio ◽  
Site Effect ◽  
Predominant Frequency ◽  
Density Estimates ◽  
Effect Analysis ◽  
Seismic Stations ◽  
Arctic Regions ◽  
Power Spectral ◽  
The Many

Abstract The horizontal-to-vertical spectral ratio (HVSR) for seismic ambient noise is a popular method that can be used to estimate the predominant frequency at a given site. In this article, we introduce the Incorporated Research Institutions for Seismology (IRIS) Data Management Center’s (DMC’s) openly available HVSR station toolbox. These tools offer a variety of ways to compute the spectral ratio by providing different averaging routines. The options range from the simple average of spectral ratios to the ratio of spectral averages. Computations take advantage of the available power spectral density estimates of ambient noise for the seismic stations, and they can be used to estimate the predominant frequency of the many three-component seismic stations available from the IRIS DMC. Furthermore, to facilitate the identification of the peaks in HVSR profiles for the assessment of the predominant frequency of station sites, the toolbox can also process the results of HVSR analysis to detect and rank HVSR peaks. To highlight the toolbox capabilities, three different examples of possible use of this toolbox for routine site-effect analysis are discussed: (1) site effects related to thawing in Arctic regions, (2) ground-motion amplification in urban area, and (3) estimation of station VS30.

Site amplification in the San Fernando Valley, California: Variability of site-effect estimation using the S-wave, coda, and H/V methods

1997 ◽  
Vol 87 (3) ◽  
pp. 710-730 ◽  
Author(s):  
Luis Fabián Bonilla ◽  
Jamison H. Steidl ◽  
Grant T. Lindley ◽  
Alexei G. Tumarkin ◽  
Ralph J. Archuleta
Keyword(s):  
Los Angeles ◽  
Reference Site ◽  
Site Response ◽  
Spectral Ratio ◽  
Site Amplification ◽  
Spectral Ratios ◽  
S Wave ◽  
S Waves ◽  
General Geology ◽  
San Fernando

Abstract During the months that followed the 17 January 1994 M 6.7 Northridge, California, earthquake, portable digital seismic stations were deployed in the San Fernando basin to record aftershock data and estimate site-amplification factors. This study analyzes data, recorded on 31 three-component stations, from 38 aftershocks ranging from M 3.0 to M 5.1, and depths from 0.2 to 19 km. Site responses from the 31 stations are estimated from coda waves, S waves, and ratios of horizontal to vertical (H/V) recordings. For the coda and the S waves, site response is estimated using both direct spectral ratios and a generalized inversion scheme. Results from the inversions indicate that the effect of Qs can be significant, especially at high frequencies. Site amplifications estimated from the coda of the vertical and horizontal components can be significantly different from each other, depending on the choice of the reference site. The difference is reduced when an average of six rock sites is used as a reference site. In addition, when using this multi-reference site, the coda amplification from rock sites is usually within a factor of 2 of the amplification determined from the direct spectral ratios and the inversion of the S waves. However, for nonrock sites, the coda amplification can be larger by a factor of 2 or more when compared with the amplification estimated from the direct spectral ratios and the inversion of the S waves. The H/V method for estimating site response is found to extract the same predominant peaks as the direct spectral ratio and the inversion methods. The amplifications determined from the H/V method are, however, different from the amplifications determined from the other methods. Finally, the stations were grouped into classes based on two different classifications, general geology and a more detailed classification using a quaternary geology map for the Los Angeles and San Fernando areas. Average site-response estimates using the site characterization based on the detailed geology show better correlation between amplification and surface geology than the general geology classification.

scholarly journals Study on the applicability of the microtremor HVSR method to support seismic microzonation in the town of Idrija (W Slovenia)

2017 ◽  
Vol 17 (6) ◽  
pp. 925-937 ◽  
Author(s):  
Andrej Gosar
Keyword(s):  
Seismic Hazard ◽  
Resonance Frequency ◽  
Complex Geometry ◽  
Free Field ◽  
Seismic Microzonation ◽  
Clear Correlation ◽  
S Wave ◽  
Resonance Frequencies ◽  
Hvsr Method ◽  
The Town

Abstract. The town of Idrija is located in an area with an increased seismic hazard in W Slovenia and is partly built on alluvial sediments or artificial mining and smelting deposits which can amplify seismic ground motion. There is a need to prepare a comprehensive seismic microzonation in the near future to support seismic hazard and risk assessment. To study the applicability of the microtremor horizontal-to-vertical spectral ratio (HVSR) method for this purpose, 70 free-field microtremor measurements were performed in a town area of 0.8 km2 with 50–200 m spacing between the points. The HVSR analysis has shown that it is possible to derive the sediments' resonance frequency at 48 points. With the remaining one third of the measurements, nearly flat HVSR curves were obtained, indicating a small or negligible impedance contrast with the seismological bedrock. The isofrequency (a range of 2.5–19.5 Hz) and the HVSR peak amplitude (a range of 3–6, with a few larger values) maps were prepared using the natural neighbor interpolation algorithm and compared with the geological map and the map of artificial deposits. Surprisingly no clear correlation was found between the distribution of resonance frequencies or peak amplitudes and the known extent of the supposed soft sediments or deposits. This can be explained by relatively well-compacted and rather stiff deposits and the complex geometry of sedimentary bodies. However, at several individual locations it was possible to correlate the shape and amplitude of the HVSR curve with the known geological structure and prominent site effects were established in different places. In given conditions (very limited free space and a high level of noise) it would be difficult to perform an active seismic refraction or MASW measurements to investigate the S-wave velocity profiles and the thickness of sediments in detail, which would be representative enough for microzonation purposes. The importance of the microtremor method is therefore even greater, because it enables a direct estimation of the resonance frequency without knowing the internal structure and physical properties of the shallow subsurface. The results of this study can be directly used in analyses of the possible occurrence of soil–structure resonance of individual buildings, including important cultural heritage mining and other structures protected by UNESCO. Another application of the derived free-field isofrequency map is to support soil classification according to the recent trends in building codes and to calibrate Vs profiles obtained from the microtremor array or geophysical measurements.

Automatic phase identification of earthquake based on the UBDN deep network

2021 ◽  
pp. 1-10
Author(s):  
Jianxian Cai ◽  
Xun Dai ◽  
Zhitao Gao ◽  
Yan Shi
Keyword(s):  
Seismic Data ◽  
Short Term Memory ◽  
Long Term Memory ◽  
Phase Identification ◽  
S Wave ◽  
Traditional Methods ◽  
Term Memory ◽  
Seismic Stations ◽  
2008 Wenchuan Earthquake ◽  
Deep Network

Seismic data obtained from seismic stations are the major source of the information used to forecast earthquakes. With the growth in the number of seismic stations, the size of the dataset has also increased. Traditionally, STA/LTA and AIC method have been applied to process seismic data. However, the enormous size of the dataset reduces accuracy and increases the rate of missed detection of the P and S wave phase when using these traditional methods. To tackle these issues, we introduce the novel U-net-Bidirectional Long-Term Memory Deep Network (UBDN) which can automatically and accurately identify the P and S wave phases from seismic data. The U-net based UBDN strongly maintains the U-net’s high accuracy in edge detection for extracting seismic phase features. Meanwhile, it also reduces the missed detection rate by applying the Bidirectional Long Short-Term Memory (Bi-LSTM) mode that processes timing signals to establish the relationship between seismic phase features. Experimental results using the Stanford University seismic dataset and data from the 2008 Wenchuan earthquake aftershock confirm that the proposed UBDN method is very accurate and has a lower rate of missed phase detection, outperforming solutions that adapt traditional methods by an order of magnitude in terms of error percentage.

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