The single-station microtremor horizontal-to-vertical spectral ratio (MHVSR) method was initially proposed to retrieve the site amplification function and its resonance frequencies produced by ...unconsolidated sediments overlying high-velocity bedrock. Presently, MHVSR measurements are predominantly conducted to obtain an estimate of the fundamental site frequency at sites where a strong subsurface impedance contrast exists. Of the earthquake site characterization methods presented in this special issue, the MHVSR method is the furthest behind in terms of consensus towards standardized guidelines and commercial use. The greatest challenges to an international standardization of MHVSR acquisition and analysis are (1) the
what
— the underlying composition of the microtremor wavefield is site-dependent, and thus, the appropriate theoretical (forward) model for inversion is still debated; and (2) the
how
— many factors and options are involved in the data acquisition, processing, and interpretation stages. This paper reviews briefly a historical development of the MHVSR technique and the physical basis of an MHVSR (the
what
). We then summarize recommendations for MHVSR acquisition and analysis (the
how
). Specific sections address MHVSR interpretation and uncertainty assessment.
Many of the most sensitive physics experiments searching for rare events, like neutrinoless double beta (
0
ν
β
β
) decay, coherent elastic neutrino nucleus scattering and dark matter interactions, ...rely on cryogenic macro-calorimeters operating at the mK-scale. Located underground at the Gran Sasso National Laboratory (LNGS), in central Italy, CUORE (Cryogenic Underground Observatory for Rare Events) is one of the leading experiments for the search of
0
ν
β
β
decay, implementing the low-temperature calorimetric technology. We present a novel multi-device analysis to correlate environmental phenomena with the low-frequency noise of low-temperature calorimeters. Indeed, the correlation of marine and seismic data with data from a couple of CUORE detectors indicates that cryogenic detectors are sensitive not only to intense vibrations generated by earthquakes, but also to the much fainter vibrations induced by marine microseisms in the Mediterranean Sea due to the motion of sea waves. Proving that cryogenic macro-calorimeters are sensitive to such environmental sources of noise opens the possibility of studying their impact on the detectors physics-case sensitivity. Moreover, this study could pave the road for technology developments dedicated to the mitigation of the noise induced by marine microseisms, from which the entire community of cryogenic calorimeters can benefit.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Nakamura (Q Rep Railway Tech Res Inst 30:25–33,
1989
) popularized the application of the horizontal-to-vertical spectral ratio (HVSR) analysis of microtremor (seismic noise or ambient vibration) ...recordings to estimate the predominant frequency and amplification factor of earthquake shaking. During the following quarter century, popularity in the microtremor HVSR (MHVSR) method grew; studies have verified the stability of a site’s MHVSR response over time and validated the MHVSR response with that of earthquake HVSR response. Today, MHVSR analysis is a popular reconnaissance tool used worldwide for seismic microzonation and earthquake site characterization in numerous regions, specifically, in the mapping of site period or fundamental frequency and inverted for shear-wave velocity depth profiles, respectively. However, the ubiquity of MHVSR analysis is predominantly a consequence of its ease in application rather than our full understanding of its theory. We present the state of the art in MHVSR analyses in terms of the development of its theoretical basis, current state of practice, and we comment on its future for applications in earthquake site characterization.
Regression problems for magnitudes Castellaro, S.; Mulargia, F.; Kagan, Y. Y.
Geophysical journal international,
06/2006, Letnik:
165, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Least-squares linear regression is so popular that it is sometimes applied without checking whether its basic requirements are satisfied. In particular, in studying earthquake phenomena, the ...conditions (a) that the uncertainty on the independent variable is at least one order of magnitude smaller than the one on the dependent variable, (b) that both data and uncertainties are normally distributed and (c) that residuals are constant are at times disregarded. This may easily lead to wrong results. As an alternative to least squares, when the ratio between errors on the independent and the dependent variable can be estimated, orthogonal regression can be applied. We test the performance of orthogonal regression in its general form against Gaussian and non-Gaussian data and error distributions and compare it with standard least-square regression. General orthogonal regression is found to be superior or equal to the standard least squares in all the cases investigated and its use is recommended. We also compare the performance of orthogonal regression versus standard regression when, as often happens in the literature, the ratio between errors on the independent and the dependent variables cannot be estimated and is arbitrarily set to 1. We apply these results to magnitude scale conversion, which is a common problem in seismology, with important implications in seismic hazard evaluation, and analyse it through specific tests. Our analysis concludes that the commonly used standard regression may induce systematic errors in magnitude conversion as high as 0.3–0.4, and, even more importantly, this can introduce apparent catalogue incompleteness, as well as a heavy bias in estimates of the slope of the frequency–magnitude distributions. All this can be avoided by using the general orthogonal regression in magnitude conversions.
To compare the outcomes of seismic hazard models with accelerometric records, the seismic ground motion at the reference soil conditions considered by the hazard estimates must be reconstructed. Here ...we illustrate the procedure proposed and operated to this purpose in the frame of the Italian DPC-INGV-S2 project. This includes two phases: the geological/geophysical characterization of the sites to be analysed and a numerical deconvolution analysis, carried on by considering specific records representative of the maximum ground motion observed at the relevant accelerometric sites. Particular attention was addressed to manage the uncertainty associated to this kind of analysis. Results are then compared with those obtained by simply applying the “correction” coefficients provided by the Italian National Seismic Code to account for site conditions.
All-FRP (Fiber Reinforced Polymer) structures made of pultruded structural elements are common in many countries, while their dynamic characterization is by far less uncommon. We focus on the ...evaluation of the dynamic features of a pavilion entirely built with pultruded FRP elements, with the only exception of the steel bolts used for connections. The all-FRP construction, located at the IUAV University Campus (Venice, Italy) was realized after a specific call for architectural design and required complex and dedicated calculation from a structural point of view. As for any new construction, the numerical finite element model was first produced and then compared with the experimental results, acquired once the structure was completed. This implies that the validation of the numerical model could be performed only a posteriori. The experimental dynamic characterization of the structure was performed according to the principles of the operational modal analysis, that is exploiting ambient microtremors as excitation for the structure. The same technique was exploited to assess the dynamic behaviour of foundation subsoil. The comparison between the experimental and the model turns out to be interesting, because the dynamic characteristics of all FRP constructions are still widely unknown in the current literature.
In the Kribi region (south-western Cameroon), a new industrial harbour has been built. This area is marked as a low-seismicity zone, according to the global seismic hazard map. This estimate is ...based, however, on a poorly documented data set. Industrial harbours are critical facilities and, consequently, appropriate cautions have to be taken in the seismic design. This paper illustrates the methodology adopted to compute the expected ground motion for the seismic design of the new harbour, starting from the available information. The standard probabilistic seismic hazard assessment is based on a logic tree approach considering areal and fault sources with two earthquake rate models (characteristic earthquake and Gutenberg–Richter), and two ground motion prediction equations. As expected, the obtained ground motion at the bedrock for a return period of 475 years is not very large 0.07 g, in terms of horizontal peak ground acceleration (PGA) with a well marked peak between 0.1 and 0.2 s. This result is in agreement with that of the Global Seismic Hazard Assessment Project, where a general PGA between 0.04 and 0.08 g is associated with south-western Cameroon. The effects of local site conditions are evaluated through geophysical methods (single station and array surveys) and 1D linear-equivalent numerical modelling. Considering the two geotechnical models identified in the study region, by a specific geophysical survey executed during this study, local amplifications of 1.9 and 2.2 have been calculated for the two sectors, respectively. Furthermore, the results obtained, in terms of uniform hazard response spectra, have been used as guidelines to determine the design ground motions for the maritime and land infrastructures planned in the Kribi harbour area. This study represents a summary of the present knowledge on the seismicity of this part of Africa as well as the first regional and local seismic hazard assessment for the Kribi area.
Earthflows are widespread phenomena in the Mediterranean area. These landslides involve fine-grained soils and clay-bearing rocks, and despite their low speed are responsible for significant economic ...losses in vast areas. The dynamics of these landslides is still relatively obscure thus reducing our ability to forecast and mitigate their effects. In this study, we present a methodological approach for the characterization of active earthflows based on the combination of geophysical surveys, laboratory tests, and empirical formulas. Geophysical surveys consist of periodic measurements of Rayleigh wave velocities repeated over time to evaluate the change of stiffness with time of the landslide material. Laboratory tests combine Atterberg limits, fall cone and oedometric tests and allow to constrain the empirical correlations between geophysical and geotechnical properties. The method is designed to obtain relevant data when direct methods like boreholes or geotechnical soundings are not possible for safety reasons, with the aim of investigating the solid-to-fluid transition that can occur in rapid earthflows. We applied this approach to study the Montevecchio landslide (Northern Apennines of Italy), an active earthflow in young marine clays which was affected by multiple reactivations in the recent years. Results show that after a surge the earthflow material is very soft (shear wave velocity in the order of 50–60 m/s) and characterized by a high water content. However, the exact value of the Liquidity Index remains unknown due to the lack of direct measurements and to the uncertainty dictated by the empirical relationships.
•The studied earthflow experiences significant variation of soil stiffness and void ratio during rapid motion.•Shortly after a surge, the material is very soft and the Liquidity Index is remarkably high.•Geophysical measurements and field observations suggest that the earthflow was fully fluidized during rapid motion.•The combination of geophysical surveys and laboratory tests allows to collect relevant data on active earthflows
This paper proposes a HVSR (horizontal to vertical spectral ratio)-based approach to assess a deep and dynamically compacted fill area in Western Sydney. In addition to recognizing that the ...predominant resonance peak of the HVSR curve is a reflection of the impedance contrast between the surface layers and bedrock, the present paper recognizes that the secondary resonance peaks of the curve at higher frequencies may reflect strong impedance contrast within surface layers. This concept has been applied to develop a methodology of HVSR-based approach relying on the measurement of the HVSR of microtremors at measuring stations, and calibration and verification by independent mechanical and MSOR (multichannel simulation with one receiver) tests. The use of MSOR tests is introduced in this paper to facilitate the calibration of the HVSR forward model, particularly in terms of providing information for the initial guess of the shear wave velocity, Vs, profile in the HVSR forward modelling. The present paper demonstrates the effective use of the HVSR-based approach to assess dynamic compaction in the gaps away from and not covered by the mechanical tests. The mapping between the depth of bedrock and the predominant resonance frequency is also extended to include the mapping of the depths of layers with strong impedance contrasts to the secondary resonance peaks, after the data have been verified by independent mechanical tests.
► We discuss the HVSR technique for the evaluation of dynamic compaction. ► Method is developed using HVSR technique with limited number of CPT and MSOR tests. ► Proposed method is verified using independent mechanical CPT and DMT data.
Ground improvement works are commonly required to overcome poor underlying soils in conjunction with infrastructure and housing development. An extensively employed and popular improvement technique ...is to impart mechanical compaction to the ground in an effort to achieve adequate strength and favourable load-deformation behaviour (stiffness) for the construction of civil infrastructure, including buildings and roads. This paper describes the study of a passive ambient vibration (often also known as microtremors) HVSR based method for assessing compacted ground. Two methods to control this compaction process at a very large site were employed: (a) strictly controlled rolling compaction (b) visually monitored (by naked eye) rolling compaction. The key features of the measured HVSR curves have been studied and analysed to infer useful insights about the compaction achieved by the two methods. Furthermore, the fitting of these measured HVSR curves by trial-and-error forward modelling forms the basis for inferring the shear wave velocity (Vs) profile and layer thicknesses of the compacted ground. It is shown in this paper that the process of analysing and interpreting the HVSR curves, as well as the forward modelling of the HVSR curves reveal useful information about the quality and consistency of the compacted ground.
► We discuss the HVSR technique for compaction assessment.► Two distinct yet complimentary methods are proposed, by interpretation and forward modelling.► The proposed methods are applied to two rolling compacted sites.
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