Multiple Lapse Time Window Research Articles

Attenuation of seismic waves in Central Egypt

Attenuation of seismic waves in central Egypt had never been studied before. The results of the research on the seismic attenuation are based upon the information collected by the seismological network from 1998 to 2011. 855 earthquakes were selected from the Egyptian seismological catalog, with their epicenter distances between 15 and 150km, their magnitudes ranging from 2 and 4.1 and focal depths reaching up to 30km. The first systematic study of attenuation derived from the P-, S- and coda wave in the frequency range 1–24Hz is presented. In the interpretation of the results both single and multiple scattering in a half space are considered. The single scattering model proposed by Sato (1977) was used. Two methods, the coda (Qc) and the Multiple Lapse Time Window (MLTW) method are used. The aim of this study is to validate these interpretations in the region and to try to identify the effects of attenuation due to intrinsic (Qi) and scattering attenuation (Qsc). The mean Qc value calculated was Qc=(39±1)f1.0±0.009. The average Qc at 1.5Hz is (53±6) and Qc=(900±195) at 24Hz with Qo ranging between 23 and 107, where η ranging between 0.9 and 1.3. The quality factor (Q) was estimated from spectra of P- and S-waves by applying a spectral ratio technique. The results show variations in Qp and QS as a function of frequency, according to the power law Q=56η1.1. The seismic albedo is 0.7 at all stations and it mean that the earthquake activity is due to tectonic origin. The attenuation and frequency dependency for different paths and the correlation of the results with the geotectonic of the region are presented. The Qc values were calculated and correlated with the geology and tectonics of the area. The relatively low Qo and the high frequency dependency agree with the values of a region characterized by a low tectonic activity and vise versa.

Envelope Inversion Analysis for High-Frequency Seismic Energy Radiation from the 2011 Mw 9.0 Off the Pacific Coast of Tohoku Earthquake

Abstract I study S ‐wave energy radiation in higher frequencies of 1–8 Hz from the 2011 M w 9.0 Off the Pacific Coast of Tohoku, Japan, earthquake (hereafter called the Tohoku‐Oki earthquake) based on a seismogram envelope inversion method. I first evaluate two medium parameters of scattering attenuation and intrinsic absorption for S waves using spatial and temporal distributions of seismic energy from aftershock records, which are necessary for calculating Green’s functions. Next, applying the envelope inversion method to 27 near‐field strong‐motion records from the mainshock, I estimate the S ‐wave energy radiation from 40 subfaults on the fault of 500 km×250 km. Each subfault is allowed to rupture for eight consecutive source time windows. Rupture velocity and the duration of energy radiation for each time window are determined by a grid search to be 2.5 km/s and 8.0 s, respectively. Energy radiated from the entire fault is 5.8×10 16 J for 1–2 Hz, 4.5×10 16 J for 2–4 Hz, 1.5×10 16 J for 4–8 Hz, and totaling 1.2×10 17 J in the 1–8 Hz range. Strong energy emanated twice from greater depths of the off‐Miyagi region, corresponding to two peaks seen at the northern stations. And energy radiation at greater depths off the Fukushima–Ibaraki border is compatible with a single peak found at the southern stations. Strong high‐frequency radiations at greater depths strikingly contrast with large slips at shallower depths estimated in lower frequencies. This frequency‐dependent rupture may accord with structural changes along the dip direction. Online material: Snapshots of high‐frequency energy radiation from the fault plane and results of estimating scattering parameters by the multiple lapse time window analysis in 1–2 and 2–4 Hz.

Depth-dependent intrinsic and scattering seismic attenuation in north central Italy

SUMMARY In this study the attenuation mechanism of seismic wave energy in north central Italy is estimated using low-magnitude earthquake local data recorded at six stations managed by INGV. Most of the analysed events are located along the Alpine chain in the zone of Iseo and Garda lakes, while a minor part in the Po valley. The zone investigated is characterized by the occurrence of significantly intense earthquakes (magnitude up to 6.6) the most recent occurred in 2004 close to the city of Salo on the coast of the Garda lake (Mw= 5.0). Due to the high population density and presence of industrial activity the investigated area is characterized by a high seismic risk. First, the ordinary Multiple Lapse Time Window Analysis (MLTWA) method is applied in the assumption of uniform velocity and scattering and the couple of B0, the seismic albedo and Le−1, the extinction length inverse (corresponding to the total attenuation coefficient) is calculated in the frequency bands of 1.5, 3, 6 and 12 Hz. To retrieve more realistic estimates, the obtained values of B0 and Le−1 are corrected taking into account the effects of a depth-dependent earth model, consisting of an earth structure characterized by a transparent upper mantle and a heterogeneous crust. We find that the corrected intrinsic and scattering attenuation parameters (which are proportional to the inverse of the intrinsic/scattering quality factors, Q−1I and Q−1S) are strongly frequency dependent, with a prevalence of scattering attenuation over the intrinsic dissipation. The corrected and uncorrected values of total Q are in agreement with the total Q values obtained with different approaches for the same area.

Attenuation Characteristics of Taiwan: Estimation of Coda Q, S-wave Q, Scattering Q, Intrinsic Q, and Scattering Coefficient

Research Article| September 01, 2010 Attenuation Characteristics of Taiwan: Estimation of Coda Q, S-wave Q, Scattering Q, Intrinsic Q, and Scattering Coefficient Fangyin Zhang; Fangyin Zhang 1Weidlinger Associates Inc., 375 Hudson Street, New York, NY 10014, USA Search for other works by this author on: GSW Google Scholar Apostolos S. Papageorgiou Apostolos S. Papageorgiou 2Department of Civil Engineering, University of Patras, Patras, Greece Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2010) 81 (5): 769–777. https://doi.org/10.1785/gssrl.81.5.769 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Fangyin Zhang, Apostolos S. Papageorgiou; Attenuation Characteristics of Taiwan: Estimation of Coda Q, S-wave Q, Scattering Q, Intrinsic Q, and Scattering Coefficient. Seismological Research Letters 2010;; 81 (5): 769–777. doi: https://doi.org/10.1785/gssrl.81.5.769 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search A dataset of 5,499 seismograms recorded at 71 short-period stations (distributed over the island of Taiwan) and generated by 108 earthquake events that occurred over a period of time from 2000 to 2003, with a magnitude ranging from ML = 3.0 to 5.0 and depths from 2.0 km to 31.0 km, were used to estimate attenuation characteristics of the lithosphere of Taiwan. The results of the analyses provide evidence that: 1) The S-wave attenuation \(Q_{{\beta}}^{-1}\) (as estimated from the coda normalization method) is in very good agreement with total attenuation \(^{T}Q_{S}^{-1}\) (as estimated from multiple lapse time window... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Study of attenuation mechanism for Garwhal–Kumaun Himalayas from analysis of coda of local earthquakes

The relative contribution of intrinsic ( Q i − 1 ) and scattering ( Q s − 1 ) attenuation to seismic wave attenuation was estimated for the Garwhal–Kumaun Himalayas using Multiple Lapse Time Window Analysis (MLTWA) method under the assumption of isotropic scattering. Local earthquake data recorded by an array operated by Wadia Institute of Himalayan Geology (WIHG), India was used for this purpose. It is observed that scattering attenuation primarily contributes to seismic wave attenuation in this region and its value is much higher compared to that of intrinsic attenuation at around 1 Hz frequency. As frequency increases the relative contribution of scattering attenuation to total attenuation starts decreasing. However, as seismic albedo is higher than 0.5 for all the frequencies considered, it is concluded that the medium here is highly heterogeneous in nature.

Depth dependent seismic scattering attenuation in the Nuevo Cuyo region (southern central Andes)

In the present work we separated intrinsic from scattering attenuation coefficients both for the crust and the upper mantle in the tectonically highly active areas of the Southern‐Central Andes ‐ Nuevo Cuyo region, analyzing two groups of earthquakes, well separated in depth. This region is characterized by the presence of flat subduction. We apply MLTWA (Multiple Lapse Time Window Analysis), coda normalization and Q‐coda techniques to measure the scattering and intrinsic attenuation coefficient and the total Q for S waves. We find that intrinsic attenuation does not decrease with depth whereas scattering attenuation is higher in the crust than in the upper mantle, and that intrinsic attenuation predominates over scattering attenuation. We interpret this observation in terms of the release of water and other fluids into the overlying lithosphere due to the dynamics of the subduction process, in agreement with most of the prevalent geodynamic models.

Spatial distribution of scattering loss and intrinsic absorption of short-periodSwaves in the lithosphere of Japan on the basis of the Multiple Lapse Time Window Analysis of Hi-net data

SUMMARY Propagation of short period S waves through the crust is strongly controlled by scattering loss and intrinsic absorption. Scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates. Since both parameters have a different effect, it is possible to compute them by means of the Multiple Lapse Time Window Analysis (MLTWA). In this paper, high resolution maps of Japan for both seismic S-wave attenuation parameters are obtained by using the MLTWA with data provided by the Hi-net seismic network. The maps show strong regional variation of the parameters. The variations depend mainly on the tectonic setting of each region and volcanism mechanisms. In the scattering loss maps, in the 1–2 Hz map, there is a very different behaviour between the northeast (stronger scattering loss) and the southwest (much weaker scattering loss). In the northeast of Japan, areas with strong scattering loss correspond mainly to the location of the volcanic arcs. In Southwest Japan, Chugoku region and the west side of Kii peninsula show strong scattering levels for the 4–8 Hz and higher frequency bands. In Hokkaido, strong scattering loss and intrinsic absorption can be observed for the lower frequency bands. In the Sendai plain, we find strong scattering loss for all the frequency bands. Under all these areas low velocity anomalies have been detected in previous works. In Tohoku area the east side shows lower intrinsic attenuation than the west side. This characteristic seems to extend to the southern part of Hokkaido and to central Japan. In Kanto area, the values of intrinsic absorption are lower than in the surrounding areas; but in the region around the Itoigawa-Shizuoka tectonic line and in its western side strong absorption areas are observed. The behaviour of each area for intrinsic absorption is similar to the behaviour observed in the Q−1c maps. The MLTWA is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption. Although these hypotheses are very simple, the results are very informative on the characteristics of each region, and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust.

Frequency-dependent attenuation of S-waves in the Kanto region, Japan

AbstractApparent, scattering, and intrinsicS-wave attenuations (QS−1,Qscat−1andQint−1) of the upper lithosphere in the Kanto region of Japan were measured in the 1- to 32-Hz frequency range using Multiple Lapse Time Window Analysis (MLTWA) for 115 borehole seismograms of local earthquakes. A new set of time windows for MLTWA, in which multiple isotropic scattering is assumed, was proposed and employed to estimate the frequency dependence ofS-wave attenuation parameters. Scattering attenuation was found to dominate intrinsic attenuation in theS-wave attenuation mechanism at low frequencies (<;2 Hz), whereas the opposite relation was observed at high frequencies. The transition is caused by the different frequency dependences ofQscat−1(∝f−1.5) andQint−1(∝f−0.7) at this frequency. Interestingly,Qscat−1is almost frequency independent at frequencies >8 Hz, which implies the self-similar nature of short-wavelength heterogeneities in the upper lithosphere. In terms of the upper lithosphere of the Kanto region, these results may indicate that the random heterogeneities characterized by the Gaussian autocorrelation function with a fractional fluctuationε≈ 10% and a correlation lengtha≈ 2 km are superimposed on the weak background self-similar heterogeneity.

Intrinsic and scattering attenuation of the Mt Fuji Region, Japan

Mount Fuji is the focus of intense study because of its potential hazard signaled by seismic, geologic and historical activity. Based on extensive seismic data recorded in the vicinity of Mt Fuji, coda quality factor (Q−1C) using a single scattering model hypothesis, and intrinsic and scattering quality factor (Q−1i and Q−1S) using the Multiple Lapse Time Window (MLTW) method were measured. To focus the study on the magmatic structure below Mt Fuji, the data were separated into two groups: a near-Fuji region of rays traversing an area with radius 5 km around the summit (R < 5 km), and a far-Fuji region of rays beyond a radius of 20 km around the summit (R > 20 km). This classification shows the largest discrepancy of Q−1C at a range of sampling volumes corresponding to overlapped sampling depth of about 80 km. Further, the spatial division shows significant difference of Q−1i and Q−1s at hypocentral distance of 80 km. The large difference of Q−1s in bandwidths 2–4, and 4–8 Hz indicates lithospheric heterogeneity beneath Mt Fuji with a characteristic heterogeneity scale length of about 1 km. The results have a small error range due to the large data sample, showing that all Q−1 values in the near-Fuji area are greater than those of the far-Fuji area, and Q−1i for both the near and far-Fuji areas is higher than Q−1s at high frequencies. The Q−1i and Q−1s values for far-Fuji are in the range of values for typical non-volcanic areas. The Q−1i values of the near-Fuji area are lower than those of other volcanic areas considered, where as values of Q−1s are not. The low Q−1i for the volcanic region of near-Fuji suggests that the magmatic activity, indicated by percent partial melt, in the vicinity of Mt Fuji is not as active as hot spot volcanoes, such as Kilauea, Hawaii.

Estimation of shear-wave attenuation characteristics for the Klyuchevskoi volcanic edifice

This paper reports a study of intrinsic attenuation and scattering in the Klyuchevskoi volcanic edifice. The data set consisted of small volcano-tectonic earthquakes occurring as deep as 30 km beneath Klyuchevskoi Volcano and recorded by radio telemetry seismograph stations installed on the edifice and near it. The digital seismograms of small volcano-tectonic earthquakes were processed by the multiple lapse time window analysis (MLTWA) method currently in use in seismology. The method uses experimental normalized integrals of 3D seismic energy density determined from several time windows applied to earthquake records that have been put through bandpass filters. The parameters that characterize the intrinsic attenuation and scattering of seismic energy of small volcano-tectonic earthquakes in Klyuchevskoi Volcano were estimated by adjusting the coefficients to ensure the best fit between experimental and theoretical integrals. An analytical solution to the seismic energy transfer equation was used to calculate the theoretical integrals of 3D seismic energy. Reliable estimates of the parameters that characterize the intrinsic attenuation and scattering in the material of the Klyuchevskoi volcanic edifice have been obtained. Our estimates of the Q for the edifice are below those derived by other workers for the Kamchatka lithosphere.

Intrinsic and Scattering Seismic Attenuation in Southwestern Anatolia

The intrinsic dissipation and scattering attenuation in southwestern (SW) Anatolia, which is a tectonically active region, is studied using the coda waves. First the coda quality factor (Q c ) assuming single scattering is estimated from the slope of the coda-wave amplitude decay. Then the Multiple Lapse Time Window (MLTW) analysis is performed with a uniform earth model. Three non-overlapping temporal data windows are used to calculate the scattered seismic energy densities against the source-receiver distances, which, in turn, are used to calculate separate estimates of the intrinsic and scattering factors. In order to explore the frequency dependency, the observed seismograms are band pass-filtered at the center frequencies of 0.75, 1.5, 3.0, 6.0 and 12.0. The scattering attenuation (Q s −1) is found lower than the intrinsic attenuation (Q i −1) at all frequencies except at 0.75 Hz where the opposite is observed. Overall the intrinsic attenuation dominates over the scattering attenuation in the SW Anatolia region. The integrated energy curves obtained for the first energy window (i.e., 0–15 s) are somewhat irregular with distance while the second (i.e., 15–30 s) and third (i.e., 30–45 s) data windows exhibit more regular change with distance at most frequencies. The seismic albedo B0 is determined as 0.61 at 0.75 Hz and 0.34 at 12.0 Hz while the total attenuation factor denoted by L e −1 changes in the range 0.034–0.017. For the source-station range 20–180 km considered the scattering attenuation is found strongly frequency dependent given by the power law Q s −1 = 0.010*f−1.508. The same relations for Q i −1, Q t −1 (total), Q c −1 and $${\tilde{Q}}^{{- 1}}_{c}$$ (expected) hold as Q i −1 = 0.0090*f−1.17, Q t −1 = 0.019*f−1.31, Q c −1 = 0.008*f−0.84 and $${\tilde{Q}}_{c}^{{- 1}} = 0.014*f^{{- 0.87}},$$ respectively. Compared to the other attenuation factors Q c −1 and $${\tilde{Q}}^{{- 1}}_{c}$$ are less dependent on the frequency.

Intrinsic attenuation and scattering of shear waves in the lithosphere of Kamchatka

Records of small local Kamchatka earthquakes were processed using Multiple Lapse Time Window Analysis (MLTWA). The method makes use of normalized integrals of 3D seismic energy density in several windows applied to an earthquake record that has been put through a bandpass filter. The intrinsic attenuation and scattering properties of the earth were estimated by choosing parameters that provide the best agreement between experimental and theoretical integrals as functions of hypocentral distance. The theoretical normalized integrals as functions of distance were computed using an analytical solution to the equation of seismic energy transport based on a simple model of isotropic scattering for scalar seismic waves excited by an impulse point source in an earth that is uniform as to scattering and intrinsic attenuation. The resulting estimates of attenuation and scattering parameters are similar to those derived in other studies of Kamchatka, as well as of other continents: America (California, US), Europe (the Canary Is., Spain, and Italy), and Asia (Japan).

Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 2001 Kachchh earthquake

176 vertical-component, short period observations from aftershocks of the M w 7.7, 26 January, 2001 Kachchh earthquake are used to estimate seismic wave attenuation in western India using uniform and two layer models. The magnitudes ( M w ) of the earthquakes are less than 4.5, with depths less than 46 km and hypocentral distances up to 110 km. The studied frequencies are between 1 and 30 Hz. Two seismic wave attenuation factors, intrinsic absorption ( Q i − 1 ) and scattering attenuation ( Q s − 1 ) are estimated using the Multiple Lapse Time Window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. We first assume spatial uniformity of Q i − 1 , Q s − 1 and S wave velocity ( β). A second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient ( g), intrinsic absorption strength ( h), density of the media ( ρ) and shear wave velocity structure. The predicted coda envelopes are computed using Monte Carlo simulation. Results show that, under the assumption of spatial uniformity, scattering attenuation is greater than intrinsic absorption only for the lowest frequency band (1 to 2 Hz), whereas intrinsic absorption is predominant in the attenuation process at higher frequencies (2 to 30 Hz). The values of Q obtained range from Q t = 118, Q i = 246 and Q s = 227 at 1.5 Hz to Q t ≈ 4000, Q i ≈ 4600 and Q s ≈ 33,300 at 28 Hz center frequencies, being Q t − 1 a measure of total attenuation. Results also show that Q i − 1 , Q s − 1 and Q t − 1 decrease proportional to f − ν . Two rates of decay are clearly observed for the low (1 to 6 Hz) and high (6 to 30 Hz) frequency ranges. Values of ν are estimated as 2.07 ± 0.05 and 0.44 ± 0.09 for total attenuation, 1.52 ± 0.21 and 0.48 ± 0.09 for intrinsic absorption and 3.63 ± 0.07 and 0.06 ± 0.08 for scattering attenuation for the low and high frequency ranges, respectively. Despite the lower resolution in deriving the attenuation parameters for a two layered crust, we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle. Also, for a crustal layer of thickness 42 km, intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle, respectively.

Attenuation study in the Straits of Messina area (southern Italy)

The attenuation of seismic waves is one of the basic physical parameters used in seismological studies and earthquake engineering, which is closely related to the seismicity and regional tectonic activity of a particular area. In this work, the seismic attenuation in the Straits of Messina, affected by several and strong historical earthquakes, was studied using waveforms recorded by a local seismic network composed of seven stations. We measured: the coda quality factor ( Q c) in the Single Scattering model hypothesis; the direct quality factor ( Q d) applying the Coda Normalization method for S-waves; and the intrinsic and scattering quality factor ( Q i and Q s) by the Multiple Lapse Time Window Analysis (MLTWA) method. Coda Q values were obtained using different lapse times (40, 60 and 80 s) for the frequency bands centred at 1.5, 3, 6 and 12 Hz. Our findings indicate that Q c increases with increasing lapse time and that Q c is frequency dependent. This behaviour is usually correlated to the degree of tectonic complexity and to the presence of heterogeneities at several scales. In fact, by using the Coda Normalization method we obtained low Q d values, as expected for a heterogeneous and active zone. Finally, by the MLTWA method we observe that the contribution of the scattering attenuation ( Q s − 1 ) prevails on the intrinsic absorption ( Q i − 1 ) until 3 Hz. Conversely, Q i − 1 and Q s − 1 seem to be of the same order in the higher frequency bands.

S-waves attenuation and separation of scattering and intrinsic absorption of seismic energy in southeastern Sicily (Italy)

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes (1.5 ≤ML≤ 4.6) recorded in the period 1994–2003. We first estimated the quality factor of S waves (QS) and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5–15 Hz. The average QS as function of frequency is given by QS= 49f0.88. A detailed separation of scattering attenuation (Q−1s) from intrinsic absorption (Q−1i) was also attempted by applying the multiple lapse time window analysis (MLTWA), under the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Intrinsic absorption dominates over scattering in the attenuation process at high frequencies (above 3 Hz). Below 3 Hz scattering is the predominant attenuation effect in the region, at the scale length of these frequencies. However, some discrepancies have been observed between the theoretical model and the observations. This indicates that models with depth-dependent velocity structure and/or non isotropic scattering should be taken into account in order to remove ambiguities in the interpretation of the results.

Characteristics of coda wave attenuation in Yunnan area

The characteristic of seismic coda wave attenuation in Yunnan area in 7 frequency-bands range from 1 Hz to 20 Hz was estimated by using the local earthquake’s waveform data recorded from 22 Yunnan digital seismic stations. Coda attenuation Q c −1 of each station was firstly calculated by single scattering method. Then, mean free path L e and seismic albedo B 0 of each station were calculated, and scattering attenuation Q s −1 and intrinsic attenuation Q i −1 were separated from total attenuation Q t −1 by multiple lapse time window analysis based on the multiple scattering model in uniform random isotropic scattering medium. The attenuating characteristics in Yunnan show that most value of L e are in 10–30 km, with maximal within 2–6 Hz; B 0 are about 0.5 at 1–2 Hz, but less than 0.5 at other frequency-bands, which means Q i −1 is comparable with Q s −1 at 1–2 Hz, and after 1–2 Hz, Q i −1 is greater than Q s −1 and dominates the attenuation process. Q c −1 is close to Q i −1 at other frequency bands except 1–2 Hz. Results show that Q −1 especially Q s −1 varies spatially, Q −1 in eastern Yunnan zone is a bit higher than in north-western Yunnan zone; northwestern Yunnan zone higher than southwestern Yunnan zone. Comparing with other results in global, Q s −1 in Yunnan is lower than the global average value among these results, Q i −1 is higher than the global average value, and Q t −1 lies the middle among these results.

Regional estimation of Q from seismic coda observations by the Gauribidanur seismic array (southern India)

Attenuation properties of the lithosphere in southern India are estimated from 1219 vertical-component, short-period observations of microearthquake codas recorded by the Gauribidanur seismic array. The magnitudes of the earthquakes range from 0.3 to 3.7 and have focal depths less than 10 km. Coda-wave attenuation ( Q c −1) is estimated by means of a single isotropic scattering method and a multiple lapse time window analysis based on the hypothesis of multiple isotropic scattering and uniform distribution of scatterers is used to estimate the contribution of intrinsic absorption ( Q i −1) and scattering ( Q s −1) to total attenuation ( Q t −1). All the attenuation parameters are estimated, as a function of frequency for hypocentral distances up to 255 km. Results show a frequency dependent relation of the Q c −1 values in the range 1–10 Hz that fit the power law Q −1(f)=Q 0 −1(f/f 0) ηA Q 0 −1 value of 0.014 and a decrease of f −1.2 have been found using data from the whole region. On the other hand, scattering attenuation is found to be greater than intrinsic absorption for all the frequency bands. A high value of the seismic albedo (which ranges from 0.68 to 1) is found which indicates that scattering is the dominant effect in the study region. Nevertheless, the attenuation parameters estimated are much lower than the obtained for other regions in the world. On the other hand, the observed energy at 0–15 s from the S-wave arrival time bends significantly downward with decreasing distance. In order to clarify this phenomenon, there is a need to take into account the vertical varying velocity structure in the theoretical model.

Intrinsic absorption and scattering attenuation in the southern part of the Netherlands

We present the first systematic study of attenuation derived from the S-wave coda in the frequency range 1-32 Hz for the southern part of the Netherlands and its surroundings. For this we used two methods, the codaQ (Q c) method and the Multiple Lapse Time Window (MLTW) method. In the interpretation of the results both single and multiple scattering in a half space are considered. Our aim is to validate these interpretations in our region and to try to identify theeffects of attenuation due to intrinsic absoprtion (Q i)and scattering attenuation (Q s). For this we analyzedmore than 100 3-component high-quality digital seismograms from 43 crustalevents and 23 different stations in the Netherlands, Germany and Belgium.Coda Q results show smaller Q c (=Q 0fn) values for epicentral distances shorter than 25 km (Q 0=90) compared to larger epicentral distances (Q 0=190), but similar frequency dependence (∝f-0.9). Interpretation of MLTW results provided a seismic albedo smaller then 0.5, suggesting that the intrinsic absorption dominates over scattering in this region. Both Q i and Q s show similar frequency dependences as Q c. These results are comparable to those obtained in other areas, but we also show that more sophisticated models are required to remove ambiguities in the interpretation. For short lapse times and shortevent-station distances we find for the simple half space model a correspondinginterpretation of both methodologies, where Q c correspondsto Q t, suggesting that a model with single scattering in ahalf space is appropriate. For long lapse times and long event station distances, however, we find that the S-wave coda is, most probably, too much influenced by crust-mantel heterogenities and more sophisticated Qinversion models using larger data sets are required for more reliable attenuation estimates.

Seismic coda attenuation after theMw= 6.2 Armenia (Colombia) earthquake of 25 January 1999

[1] Seismic wave attenuation in the central region of the Colombian Andes is studied using coda waves. Most of the events used occurred in the region on the occasion of the Armenia 25 January 1999 earthquake. The estimation of the decay rate of coda amplitudes (called coda Q−1 or Qc−1) is performed by means of the single isotropic scattering method of Sato [1977]. The attenuation parameters Qi−1 (intrinsic absorption), Qs−1 (scattering loss), and Qt−1 (total attenuation) are also estimated using the multiple lapse time window method of Hoshiba et al. [1991]. The frequencies of interest lie between 1 and 15 Hz. Results show that scattering attenuation is predominant for the frequency bands 1.5 ± 0.5 and 13.5 ± 1.5 Hz, whereas the intrinsic absorption and scattering contribute in equal shares to total attenuation for the 3 ± 1, 5 ± 1, 7.5 ± 1.5, and 10.5 ± 1.5 Hz frequencies. A comparison among the estimated attenuation parameters indicates that Qc−1 is close to total attenuation for all the studied frequency bands. On the other hand, no evidence in support of temporal changes of Qc−1 before and after the main shock has been found. Finally, the regionalization of Qc−1 values seems to correlate well with the geotectonic characteristics of the region.

Scattering and anelastic attenuation of seismic energy in the vicinity of north anatolian fault zone, eastern Turkey

Erzincan basin, eastern Turkey, is seismically very active pull-apart basin and developed in between the eastern segments of the north anatolian fault zone. A study of the regional and site attenuation of seismic waves of earthquakes in this area will contribute in predicting earthquake generated ground-motion and becomes vital in making decisions for earthquake regulations and building codes, especially for the cities on the north anatolian fault zone. In this paper, anelastic and scattering attenuation in Erzincan region is investigated by using of multiple lapse time window (MLTW) method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatters. It is found that the scattering and intrinsic Q −1 are almost equal for 3 Hz and lower frequencies and intrinsic attenuation is dominant over scattering attenuation for 6 Hz and higher frequencies. Model fitting was quite good for almost all frequencies at long distances, more scattered data and observed poor model fitting at low frequencies (1.5 Hz) and short distances (5–15 km) may indicate the complexities in the shallower part of crust in Erzincan. The seismic albedo is 0.52 for 1.5 Hz and 0.32 for 12 Hz. L e −1 value increases slightly with frequency as 0.058 for 1.5 Hz and 0.032 for 12 Hz. The coda Q c −1 determined from the decay rate of coda waves is similar to Q s −1 for 1.5 and 3 Hz and it is close to Q t −1 for frequencies higher than 3 Hz. We found that the scattering attenuation is strongly frequency dependent, decreasing proportional to f 1.48 whereas intrinsic Q i −1 is considerably less frequency dependent f 1.1. A decrease of Q s −1 faster than f 1.0 with increasing frequency implies that the medium may be characterized by a Gaussian rather than exponential auto-correlation function.