Frequency-dependent Quality Factor Research Articles

SPECTRAL and SOURCE PARAMETERS of NORTH CAUCASUS EARTHQUAKES in 2018–2019

The dynamic parameters of the sources of 44 earthquakes in the North Caucasus were determined from the amplitude spectra of S-waves for the period 2018–2019 with an energy class according to T.G. Rautian scale KR=9.1–14.1. Earthquake records from regional digital seismic stations of the North Caucasus network, with epicentral distances of no more than 300 km were used for the calculation. The source spectra were calculated based on the frequency-dependent quality factor Q(f) for earthquakes in the North Caucasus western zone – Q(f)=90f 1.02 – and eastern zone – Q(f)=97f 0.89 . The SEISAN program was used for the spectral analysis of 31 earthquakes. The following values were obtained: 0 – spectral density, f0 – corner frequency, M0 – scalar seismic moment, Mw – moment magnitude, L – length of the rupture at the source of an earthquake, or r – radius of the circular area,  – stress drop. Relationships between lgM0 and KR and Mw and KR are obtained.

Strong motion estimation in Costa Rica at non-record sites using spectral inversion method

We performed the spectral inversion to separate the source, path, and site effects using strong ground motion records from essential facilities such as powerhouses and hydroelectric dams, distributed all over Costa Rica. The spectral inversion technique was adapted to a sparsely observed strong motion data set. We used the results to estimate strong ground motions at sites where there were no observation records in and around the intensity anomaly that appeared during the 2012 Sámara earthquake of Mw 7.6. To ensure the quality, we incorporated a broadband station to estimate levels of acceleration source spectra for six events 5.3 ≤ Mw ≤ 6.5, using them as the reference events for the spectral inversion. In this paper, we introduced two consistency checks: confirmation of the correctness of the input data, and verification of the output using synthetic spectra. We used them as an iterative implementation of sequences of elimination of suspicious data and inversions. We regulated the source spectra of the reference events for the final inversion, considering the estimate of site effect for one-dimensional SH wave propagation at the site of the lowest site amplification. We obtained the frequency-dependent quality factor Q = 179f0.5598 for the northern and central parts of Costa Rica. From the output of the spectral inversion, we reproduced the acceleration spectra of earthquakes in the sites where the event was not recorded. We applied this formulation using the earthquake mentioned above. The resulting synthetic spectra are consistent with the anomalous intensity distribution reported at that time.

SPECTRAL and FOCAL PARAMETERS of NORTHERN CAUCASUS EARTHQUAKES in 2016–2017

The source spectral and dynamic parameters for 39 earthquakes with KR=10.0–13.8 occurred in the North Caucasus for 2016–2017 are given. The parameters were determined from S-wave amplitude spectra. Records of four regional digital seismic stations («Anapa», «Kislovodsk», «Makhachkala» and «Sochi») located no more than 300 km from the sources were used. The values of the frequency-dependent quality factor Q(f) for the environment near these stations were obtained earlier. This is necessary to take into account the attenuation of S-wave energy in the Earth's crust and upper mantle in order to recalculate the station spectra into the source spectra. In 2016–2017, most of the studied earthquakes were located in the Eastern Caucasus. For the first time, for western zone earthquakes recorded by a network of stations (N=4–7), the SEISAN program was applied and satisfactory results were obtained when compared with the Crimean data for the Kerch-Kuban zone.

S-Wave Attenuation Variation and its Impact on Ground Motion Amplitudes During 2016–2017 Central Italy Earthquake Sequence

A very energetic seismic sequence struck the central Apennines, Italy, in 2016–2017, with a series of damaging earthquakes, three of them with moment magnitudes M ≥ 5.9, and five of them with M ≥ 5.0, occurred over a few months between 24 August 2016, and late 2017. Several studies explained the phenomenon of a cascading earthquake sequence with fluid movements that provoked the rupture of different parts of the fault segments at different times and locations (e.g., Miller, Nature, 2004, 427, 724–727; Gabrielli, Frontiers in Earth Science, section Structural Geology and Tectonics, 2022; Malagnini, Frontiers in Earth Science, section Solid Earth Geophysics, 2022). In this study, we investigated the variation of crustal S-wave attenuation in terms of the frequency-dependent quality factor Q(f) before and after the main events (including the Amatrice, Visso, and Norcia sub-sequences, hereafter, AVN, and periods before and after the AVN multi-mainshock sequence). The spectral characteristics of regional attenuation in the central Apennines, as well as of the earthquake sources of the AVN sequence, are derived through regression analysis using a large set of seismograms; Q(f) is modeled, together with the bilinear geometrical spreading, g(r), using a widely used tool, namely, random vibration theory, RVT (Cartwright and Longuet-Higgins, 1956). The primary objective of this effort was to examine how the variability of crustal anelastic attenuation would impact the earthquake-induced ground motions. The latter is quantified in terms of peak ground accelerations (PGAs), peak ground velocities (PGVs), and pseudo spectral accelerations (PSAs) at 0.3 and 2 s . Here, we showed that the main events of the AVN sequence strongly affect crustal S-wave attenuation, including its frequency dependence. However, the effects of 1/Q(f) fluctuations on earthquake-induced ground motions are small and have a negligible impact on the seismic hazard.

Frequency-dependent quality factor of body waves in the Kathmandu region, Nepal

The Kathmandu region becomes situated in very close to the major thrust faults such as Main Boundary Thrust (MBT) and Main Central Thrust (MCT) has been significantly affected by a series of several major earthquakes in the past. The current study analyses the attenuation of body waves in the region using the coda normalization method based on the data of two stations (NA430 and NA060) essentially from a temporary seismic network deployed after the occurrence of the 25th April 2015 earthquake. The events considered for the study have a local magnitude of 4–5.5 ​at a depth range of 10–27 ​km. The estimated quality factor of primary and secondary waves are QP = (44 ​± ​12.896)f (0.82±0.173), QS = (62 ​± ​19.265)f (0.94±0.185) for NA430 station and QP = (35 ​± ​9.467)f (0.93±0.155), QS = (68 ​± ​22.510)f (0.91±0.198) for NA060 station. The QS/QP ratio more than one observed for the entire frequency range specifies the highly heterogeneous crust medium beneath the study region. The obtained quality factors could be used in the generation of target ground motion for engineering purposes and in the calculation of source parameters for seismic hazard assessment as risk reduction strategies in the study region.

Nonlinear seismic inversion by physics-informed Caianiello convolutional neural networks for overpressure prediction of source rocks in the offshore Xihu depression, East China

Pressure prediction has long been one of subject of research focuses in petroleum geology and exploration, but is traditionally limited to moderately overpressured formations due to disequilibrium compaction based on the empirical velocity-pressure model. Overpressures in the Xihu depression are caused by fluid expansion due to the generation of natural gas in source rocks. The resulting abnormally pressured gas reservoirs manifest as a high-pressure structure with the thick mud-coated thin sand (MCS) that remains largely unaddressed in prediction. Such gas-producing overpressures make traditional prediction methods unapplicable because of the significant influence of high gas contents on seismic velocities. We employ a frequency-dependent quality factor Q–pressure petrophysical model because of the sensitivity of acoustic attenuation to overpressures. However, acoustic attenuations from rock physics and sonic logging present an uncertain dependence on pore pressures. This implies that overpressure prediction is a typical physical system that is characterized by both deterministic mechanism and statistical behavior, which resorts to physics-informed deep learning methods. We take the Q–pressure petrophysical model as the activation function of Caianiello convolutional neurons with an attempt to combine deterministic and statistical mechanisms for overpressure prediction. Such convolutional neurons render strong feature extraction and powerful learning ability and are used to construct physics-informed Caianiello convolutional neural networks (CCNNs) for overpressure prediction in the Xihu depression. The comprehensive CCNNs-based seismic inversion scheme for overpressures consists of reservoir petrophysical modeling, deep learning for neural wavelets, well-seismic correlation analysis, deconvolution-based inversion for an initial pressure model, and input-signal reconstruction to improve the initial pressure model. With drill stem tests (DSTs), well logs, and 3D seismic data, we conduct the overpressure prediction associated with cross validation in the Xihu depression, which demonstrates the applicability of the physics-informed CCNNs inversion scheme. Predicting reliability away from the training wells usually depends on the geological complexity of areas under study. Nevertheless, the information representation in the trained CCNNs can be improved gradually by feeding new well data during the development of an oil field.

Differential Crustal Attenuation in the Garhwal and Kumaon Himalaya Obtained from Seismological and Geophysical Studies

Abstract The Uttarakhand Himalaya which comprises of the Garhwal and Kumaon Himalaya lies in the central seismic gap region of India. Strong motion networks have been installed separately in the Garhwal and Kumaon Himalaya under various sponsored research projects funded by the Department of Science and Technology (DST) and Ministry of Earth Sciences (MoES). These networks have recorded several near field earthquakes in the recent past. Recorded data from these networks have been utilised to study the crustal attenuation characteristics of these two regions. The crustal attenuation characteristics of medium can be directly estimated from the frequency dependent quality factor ‘Q’. Estimation of shear wave quality factor, coda wave quality factor and attenuation relations have been made by using same methodology in the data set obtained separately from these two regions. It has been found that there is a substantial difference in the attenuation characteristics of the crustal rocks in these two regions. Since shear wave attenuation has a close relation with the shear wave velocity, therefore, the shear wave velocity has been estimated at various locations of the Garhwal and Kumaon Himalaya by both active and passive methods. It has been found that the average shear wave velocity of crustal rocks in the Garhwal Himalaya is comparatively higher than that in the Kumaon Himalaya which clearly support the high attenuation property of the crustal rocks in the Kumaon Himalaya compared to the Garhwal Himalaya.

Simulation of Pulse-Like Ground Motions during the 2015 Mw 8.3 Illapel Earthquake with a New Source Model Using Corrected Empirical Green’s Functions

Abstract Pulse-like near-source ground motions were observed by the local network during the 2015 Mw 8.3 Illapel, Chile earthquake. Such ground motions can be quite damaging to a wide range of infrastructures. The primary objective of this study is to provide a source model that can explain such ground motions. The isolated nature of the pulses indicated that the rupture of some small isolated region on the fault contributed to the generation of the pulse. Therefore, we considered such regions and termed them as Strong Motion Pulse Generation Areas (SPGAs). We used the corrected empirical Green's function (EGF) method because this method has been successfully applied to near-source pulse-like ground motions in previous studies. We simulated synthetic waveforms using the frequency dependent quality factor Q=239f0.71 and empirical site amplification factors, which we obtained by applying a generalized inversion technique to local weak-motion data. The result indicated that the observed ground motions from the Mw 8.3 Illapel earthquake can readily be explained with a source model that involves two SPGAs with dimensions of several kilometers in spite of the huge rupture zone of the earthquake. The source model can reproduce velocity waveforms, acceleration Fourier amplitude spectra (FAS) and pseudoacceleration response spectra. It also reproduces the duration of strong ground motions quite accurately. No significant bias was found with respect to distance and frequency. In conclusion, the corrected EGF method is a very efficient tool to simulate near-source ground motions of a subduction earthquake when it is combined with higher stress-drop subevents whose sizes are adjusted to the observed pulse widths.

Regional attenuation models in Central and Eastern North America using the NGA-East database

The anelastic attenuation term found in ground motion prediction equations (GMPEs) represents the distance dependence of the effect of intrinsic and scattering attenuation on the wavefield as it propagates through the crust and contains the frequency-dependent quality factor, [Formula: see text], which is an inverse measure of the effective anelastic attenuation. In this work, regional estimates of [Formula: see text] in Central and Eastern North America (CENA) are developed using the NGA-East regionalization. The technique employed uses smoothed Fourier amplitude spectrum (FAS) data from well-recorded events in CENA as collected and processed by NGA-East. Regional [Formula: see text] is estimated using an assumption of average geometrical spreading applicable to the distance ranges considered. Corrections for the radiation pattern effect and for site response based on [Formula: see text] result in a small but statistically significant improvement to the residual analysis. Apparent [Formula: see text] estimates from multiple events are combined within each region to develop the regional models. Models are provided for three NGA-East regions: the Gulf Coast, Central North America, and the Appalachian Province. Consideration of the model uncertainties suggests that the latter two regions could be combined. There were not sufficient data to adequately constrain the model in the Atlantic Coastal Plain region. Tectonically stable regions are usually described by higher [Formula: see text] and weaker frequency dependence ([Formula: see text]), while active regions are typically characterized by lower [Formula: see text] and stronger frequency dependence, and the results are consistent with these expectations. Significantly different regional [Formula: see text] is found for events with data recorded in multiple regions, which supports the NGA-East regionalization. An inspection of two well-recorded events with data both in the Mississippi embayment and in southern Texas indicates that the Gulf Coast regionalization by Cramer in 2017 may be an improvement to that of NGA-East for anelastic attenuation. The [Formula: see text] models developed serve as epistemic uncertainty alternatives in CENA based on a literature review and a comparison with previously published models.

Tidal constraints on the low-viscosity zone of the Moon

In this paper, the effect on the tidal response of the low-viscosity zone in the deep interior of the Moon is investigated based on hypothetical temperature profiles. The tidal parameters are computed numerically to demonstrate their dependence on the low-viscosity zone and frequency. One of the calculated parameters is the tidal quality factor, to which energy dissipation is inversely proportional. The other parameters are the tidal Love numbers, which are normalized magnitudes of displacement and potential perturbation of tidal deformation. Unlike earlier considerations, the viscosity structure of the low-viscosity zone is no longer assumed to be fully uniform but linked with several temperature profiles such as a thermal boundary layer model or a convective layer model. The calculations show that the latest observational ranges of the frequency-dependent quality factors can be satisfied only by the convective layer model with some viscosity value for the middle layer but not by the thermal boundary layer model for any structure. The approximate viscosity solution is estimated to be 3 × 1016 Pa s. If considering also the observational ranges of the Love numbers together with those of the quality factors, the solution of the outer radius of the low-viscosity zone is approximately either 560 or 580 km. These solutions are almost identical to those based on the previous model where the low-viscosity zone has uniform viscosity. It is concluded that the thermal state of the bottom layer of the lunar mantle is predicted to be mainly controlled by local convection, and possibly maintained by the energy balance between convective cooling and tidal heating, as previously suggested.

Seismic Wave Absorption in the Eastern Part of the North Caucasus Estimated from Records by Seismic Station “Makhachkala”

Abstract—Records of local earthquakes obtained at seismic station “Makhachkala” are used for estimating the frequency-dependent quality factor of the Earth’s crust and upper mantle in the eastern part of the North Caucasus. The records of 42 earthquakes with epicentral distances up to ~200 km and magnitudes M ~ 2.4–5.8 have been analyzed. The quality function Q(f) is estimated by coda normalization method which is applicable in different situations and yields reliable Q(f) estimates. With the assumed three-segment geometrical spreading function that is equal to 1/R at distances from 1 to 50 km from the source, 1/50 at distances 50–150 km, and 1/ $$\sqrt R $$ beyond 150 km, the quality factor is found to be Q(f) ~ 10 f 0.9, which is close to the Q-values previously established for the the medium in the vicinity of Sochi, Anapa, and Kislovodsk. The obtained quality factor estimates can be used for forecasting the parameters of ground motions during the future strong earthquakes in the eastern part of the North Caucasus. In the future studies, these estimates can be refined.

Correction of Q Factor Effects for Simultaneous Collection of Elemental Analysis and Relaxation Times by Nuclear Magnetic Resonance.

A new method for measurement of elemental analysis by nuclear magnetic resonance (NMR) of unknown samples is discussed here as a quick and robust means to measure elemental ratios without the use of internal or external calibration standards. The determination of elemental ratios was done by normalizing the signal intensities by the frequency dependent quality factor (Q) and the gyromagnetic ratios (γ) for each measured nucleus. The correction for the frequency dependence was found by characterizing the output signal of the probe as a function of the quality factor (Q) and the frequency, and the correction for γ was discussed in a previous study. A Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used for evaluation of the relative signal intensities, which allows for derivation of elemental ratios, and was correspondingly used to simultaneously measure the T2* of samples for an added parameter for more accurate identification of unknown samples.

Spectral decomposition of the Engineering Strong Motion (ESM) flat file: regional attenuation, source scaling and Arias stress drop

We perform a spectral decomposition of the Fourier amplitude spectra disseminated along with the Engineering Strong Motion (ESM) flat file for Europe and Middle East. We apply a non-parametric inversion schema to isolate source, propagation and site effects, introducing a regionalization for the attenuation model into three domains. The obtained propagation and source components of the model are parametrized in terms of geometrical spreading, quality factor, seismic moment, and corner frequency assuming a ω2 source model. The non-parametric spectral attenuation values show a faster decay for earthquakes in Italy than in the other regions. Once described in terms of geometrical spreading and frequency-dependent quality factor, slopes and breakpoint locations of the piece-wise linear model for the geometrical spreading show regional variations, confirming that the non-parametric models capture the effects of crustal heterogeneities and differences in the anelastic attenuation. Since they are derived in the framework of a single inversion, the source spectra of the largest events which have occurred in Europe in the last decades can be directly compared and the scaling of the extracted source parameters evaluated. The Brune stress drop varies over about 2 orders of magnitude (the 5th, 50th and 95th percentiles of the ∆σ distribution are 0.76, 2.94, and 13.07 MPa, respectively), with large events having larger stress drops. In particular, the 5th, 50th and 95th percentiles for M > 5.5 are 2.87, 6.02, and 23.5 MPa, respectively whereas, for M < 5.5, the same percentiles are 0.73, 2.84, and 12.43 MPa. If compared to the residual distributions associated to a ground motion prediction equation previously derived using the same Fourier amplitude spectra, the source parameter and the empirical site amplification effects correlate well with the inter-event and inter-station residuals, respectively. Finally, we calibrated both non-parametric and parametric attenuation models for estimating the stress drop from the ratio between Arias intensity and significant duration. The results confirm that computing the Arias stress drop is a suitable approach for complementing the seismic moment with information controlling the source radiation at high frequencies for rapid response applications.

Frequency-dependent quality factors from the deconvolution of ambient noise recordings in a borehole in West Bohemia/Vogtland

Frequency-dependent quality factors from the deconvolution of ambient noise recordings in a borehole in West Bohemia/Vogtland

On Strong Positive Frequency Dependencies of Quality Factors in Local-Earthquake Seismic Studies

Many observations of seismic waves from local earthquakes are interpreted in terms of the frequency-dependent quality factor \(Q\left( f \right) = Q_{0} f^{\eta }\), where η is often close to or exceeds one. However, such steep positive frequency dependencies of Q require careful analysis with regard to their physical consistency. In particular, the case of η = 1 corresponds to frequency-independent (elastic) amplitude decays with time and consequently requires no Q-type attenuation mechanisms. For η > 1, several problems with physical meanings of such Q-factors occur. First, contrary to the key premise of seismic attenuation, high-frequency parts of the wavefield are enhanced with increasing propagation times relative to the low-frequency ones. Second, such attenuation cannot be implemented by mechanical models of wave-propagating media. Third, with η > 1, the velocity dispersion associated with such Q(f) occurs over unrealistically short frequency range and has an unexpected oscillatory shape. Cases η = 1 and η > 1 are usually attributed to scattering; however, this scattering must exhibit fortuitous tuning into the observation frequency band, which appears unlikely. The reason for the above problems is that the inferred Q values are affected by the conventional single-station measurement procedure. Both parameters Q0 and are apparent, i.e., dependent on the selected parameterization and inversion method, and they should not be directly attributed to the subsurface. For η ≈ 1, parameter Q0 actually describes the frequency-independent amplitude decay in access of some assumed geometric spreading t−α, where α is usually taken equal one. The case η > 1 is not allowed physically and could serve as an indicator of problematic interpretations. Although the case \(0 < \eta < 1\) is possible, its parameters Q0 and may also be biased by the measurement procedure. To avoid such difficulties of Q-based approaches, we recommend measuring and interpreting the amplitude-decay rates (such as parameter α) directly.

High Resistivity SOI RF CMOS 인덕터의 주파수 종속 Quality Factor 모델링

High Resistivity SOI RF CMOS 인덕터의 주파수 종속 Quality Factor 모델링

Attenuation of Lg waves in the New Madrid seismic zone of the central United States using the coda normalization method

Unique properties of coda waves are employed to evaluate the frequency dependent quality factor of Lg waves using the coda normalization method in the New Madrid seismic zone of the central United States. Instrument and site responses are eliminated and source functions are isolated to construct the inversion problem. For this purpose, we used 121 seismograms from 37 events with moment magnitudes, M, ranging from 2.5 to 5.2 and hypocentral distances from 120 to 440km recorded by 11 broadband stations.A singular value decomposition (SVD) algorithm is used to extract Q values from the data, while the geometric spreading exponent is assumed to be a constant. Inversion results are then fitted with a power law equation from 3 to 12Hz to derive the frequency dependent quality factor function. The final results of the analysis are QVLg (f)=(410±38) f0.49±0.05 for the vertical component and QHLg (f)=(390±26) f0.56±0.04 for the horizontal component, where the term after ± sign represents one standard error. For stations within the Mississippi embayment with an average sediment depth of 1 km around the Memphis metropolitan area, estimation of quality factor using the coda normalization method is not well-constrained at low frequencies (f<3Hz). There may be several reasons contributing to this issue, such as low frequency surface wave contamination, site effects, or even a change in coda wave scattering regime which can exacerbate the scatter of the data.

Region-specific S-wave attenuation for earthquakes in northwestern Iran

In this study, continuous wavelet transform is applied to estimate the frequency-dependent quality factor of shear waves, QS, in northwestern Iran. The dataset used in this study includes velocigrams of more than 50 events with magnitudes between 4.0 and 6.5, which have occurred in the study area. The CWT-based method shows a high-resolution technique for the estimation of S-wave frequency-dependent attenuation. The quality factor values are determined in the form of a power law as QS(f) = (147 ± 16)f0.71 ± 0.02 and (126 ± 12)f0.73 ± 0.02 for vertical and horizontal components, respectively, where f is between 0.9 and 12 Hz. Furthermore, in order to verify the reliability of the suggested QS estimator method, an additional test is performed by using accelerograms of Ahar-Varzaghan dual earthquakes on August 11, 2012, of moment magnitudes 6.4 and 6.3 and their aftershocks. Results indicate that the estimated QS values from CWT-based method are not very sensitive to the numbers and types of waveforms used (velocity or acceleration).

Frequency dependent attenuation of seismic waves for Delhi and surrounding area, India

&lt;p align="left"&gt;The attenuation properties of Delhi &amp;amp; surrounding region have been investigated using 6&lt;em&gt;2&lt;/em&gt; local earthquakes recorded at nine stations. The frequency dependent quality factors &lt;em&gt;Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;a&lt;/sub&gt;&lt;/em&gt; (using P-waves) and &lt;em&gt;Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;b&lt;/sub&gt;&lt;/em&gt; (using S-waves) have been determined using the coda normalization method. Quality factor of coda-waves (&lt;em&gt;Q&lt;sub&gt;c&lt;/sub&gt;&lt;/em&gt;) has been estimated using the single backscattering model in the frequency range from 1.5 Hz to 9 Hz. Wennerberg formulation has been used to estimate &lt;em&gt;Q&lt;sub&gt;i&lt;/sub&gt;&lt;/em&gt; (intrinsic attenuation parameter) and &lt;em&gt;Q&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt; (scattering attenuation parameter) for the region. The values &lt;em&gt;Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;a&lt;/sub&gt;, Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;b, &lt;/sub&gt;Q&lt;sub&gt;c, &lt;/sub&gt;Q&lt;sub&gt;i&lt;/sub&gt; and Q&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt; estimated are frequency dependent in the range of 1.5Hz-9Hz. Frequency dependent relations are estimated as &lt;em&gt;Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;a&lt;/sub&gt;=52f&lt;sup&gt;1.03&lt;/sup&gt;, Q&lt;/em&gt;&lt;em&gt;&lt;sub&gt;b&lt;/sub&gt;=98f&lt;sup&gt;1.07&lt;/sup&gt; and Q&lt;sub&gt;c&lt;/sub&gt;=158f&lt;sup&gt;0.97&lt;/sup&gt;&lt;/em&gt;. &lt;em&gt;Q&lt;sub&gt;c&lt;/sub&gt;&lt;/em&gt; estimates lie in between the values of &lt;em&gt;Q&lt;sub&gt;i&lt;/sub&gt;&lt;/em&gt; and &lt;em&gt;Q&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt; but closer to &lt;em&gt;Q&lt;sub&gt;i&lt;/sub&gt;&lt;/em&gt; at all central frequencies. Comparison between &lt;em&gt;Q&lt;sub&gt;i&lt;/sub&gt; &lt;/em&gt;and &lt;em&gt;Q&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt; shows that intrinsic absorption is predominant over scattering for Delhi and surrounding region. &lt;/p&gt;

Investigation of Attenuation of theLg‐Wave Amplitude in the Caribbean Region

The focus of this study is to determine the frequency-dependent quality factor function Qffor the Caribbean region. The analysis considers the Lg portion of 2685 three-component waveforms. Waveforms are selected from 116 earthquakes that occurred between 2006 and 2013 with moment magnitude Mw ranging from 4.6 to 7.0. Spectral amplitudes over 12 distinct passbands from 0.1 to 12.8 Hz are calcu- lated only for waveforms with a signal-to-noise ratio of 5 or better. In the regression model, the vertical component and the geometric mean of two horizontal components are used to estimate Qf � . A geometrical spreading function with spectral amplitude decay of R �0:5 is used for distances beyond 100 km. The following quality factor functions for the assumed geometrical spreading are obtained: Q H � 310f 0:54 for the horizontal components, and Q V � 235f 0:65 for the vertical components.