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

A new ground-motion prediction model is developed for the response spectral ratio of vertical-to-horizontal (V/H) components of earthquakes for the Gulf Coast region. The proposed V/H response spectral ratio model has the advantage of considering the earthquake magnitude, source-to-site distance, and the shear-wave velocity of soil deposits in the upper 30 m of the site (V S30) for the peak ground acceleration, and a wide range of spectral periods (0.01-10.0 s). The model is based on a comprehensive set of regression analyses of the newly compiled Next Generation Attenuation-East database of available central and eastern North America recordings with the moment magnitudes M ≥ 3:4 and the rupture distances R Rup < 1000 km. The 50th percentile (or median) pseudospectral acceleration values computed from the orthogonal horizontal components of ground motions rotated through all possible nonredundant rotation angles, known as the RotD50 (Boore, 2010), is used along with the vertical component to perform regression using a nonlinear mixed-effects regression algorithm. The predicted V/H ratios from the proposed model are compared with the recently published V/H spectral ratio models for different regions. The derived V/H ratios can be used to develop the vertical response spectra for the sites located within the Gulf Coast region, which include the Mississippi embayment.

Section: Path Termmentioning

confidence: 99%

A Study of Vertical‐to‐Horizontal Ratio of Earthquake Components in the Gulf Coast Region

Haji‐Soltani¹,

Pezeshk

Malekmohammadi³

et al. 2017

“…Figure 9 shows the velocity model and the associated phase-velocity dispersion curve used. In real-world data, it is possible to estimate the attenuation in terms of quality factors from the seismic recordings for use in the calculations (Hosseini et al, , 2015Pezeshk et al, 2013). In this study, attenuation effects on the seismograms and dispersion curves are not considered.…”

Section: Model and Assumptionsmentioning

confidence: 99%

A Synthetic Study into the Nature and Solution of Nonuniqueness in Surface-Wave Inverse Problems

Hosseini¹,

Pezeshk²

2015

Self Cite

The solution of a Rayleigh-wave inverse problem may potentially deviate from the realistic shear-wave velocity structure due to nonuniqueness. To overcome such deviation, it is necessary to understand the source of nonuniqueness and situations that may give rise to the nonuniqueness. In this study, the existence and formation of the nonunique solutions in an inverse problem are demonstrated by modeling the solution space of a synthetic surface-wave inverse problem and investigating the major causes that might engender nonuniqueness, namely (1) the inversion convergence threshold, (2) ambient noise, (3) corner frequency of the recordings, and (4) the water level. Regarding the severity of nonuniqueness in the phase-velocity inverse problems, a technique is proposed to improve the inversion that exploits the match between the synthetic and observed time series used as a posteriori information for constraining the realistic velocity structure. Through a synthetic example, the effectiveness of such method is tested and demonstrated effective.

“…The quality factor can be estimated using frequencydomain techniques (Anderson and Hough, 1984;Chen et al, 1994;Zandieh and Pezeshk, 2010;Mousavi et al, 2014;Hosseini et al, 2015), or time-domain techniques (Wu and Lees, 1996;Zollo and de Lorenzo, 2001) for different phases of seismic waves such as body waves (primary and shear waves), surface waves, and coda waves regarding the frequency band of interest. For high frequencies, laboratory techniques are suggested, while for low frequencies, deterministic techniques are often applied.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Coda‐Wave Attenuation and Geometrical Spreading in the New Madrid Seismic Zone

Sedaghati

Pezeshk

2016

Using the single backscattering method, coda quality factor functions through coda window lengths of 20, 30, 40, 50, and 60 s have been estimated for the New Madrid seismic zone (NMSZ). Furthermore, geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method. A total of 284 triaxial seismograms with good signal-to-noise ratios (SNR > 5) from broadband stations located in the NMSZ were used. The database consisted of records from 57 local earthquakes with moment magnitudes of 2.6-4.1, and hypocentral distances less than 200 km.Q-factor values were evaluated at five frequency bands with central frequencies of 1.5, 3, 6, 12, and 24 Hz. Vertical components were utilized to estimate vertical coda Q-factor values. Horizontal coda Q-factor values were determined using the average amount of the Q-factor values estimated from two orthogonal horizontal components. The coda Q-factor increases with increasing of the coda window length implying that with increasing the depth, the coda Q-factor increases. The intermediate values of the Q-factor and intermediate values of the frequency dependency indicate that the Earth's crust and upper mantle beneath the entire NMSZ is tectonically a moderate region with a moderate to relatively high degree of heterogeneities.The geometrical spreading factors of S-wave amplitudes are frequency dependent and determined to be −0:761, −0:991, −1:271, −1:182, and −1:066 for center frequencies of 1.5, 3, 6, 12, and 24 Hz, respectively, at hypocentral distances of 10-60 km. The geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies, as well as the greater sensitivity of band-pass-filtered seismograms of small earthquakes to the noise in low frequencies.