Lapse Time Research Articles

Seismic wave attenuation in the lithosphere of the North Tanzanian divergence zone (East African rift system)

The seismic effective quality factor (QC) and its frequently dependences or the frequency parameter (n) and attenuation coefficient (δ) for the Earth’s crust and upper mantle of the North Tanzanian divergence zone (East African rift system) were estimated from an analysis of the earthquake coda waves recorded in the SEISMO-TANZ’07 French-Tanzanian seismic experiment. The QC values increase and the n and δ values decrease with increasing frequency and length of the lapse time window. This behavior of the attenuation parameters may be evidence that the degree of heterogeneity of the lithosphere decreases with depth. Comparison of the depth variations in the attenuation coefficient δ and the frequency parameter n with the velocity structure of the region shows that there is a distinct change in the behavior of seismic wave attenuation at velocity discontinuities. The obtained attenuation parameters were compared with the same parameters obtained in our previous studies for other continental rift systems—the Baikal rift system (Eurasia) and the Basin and Range Province (North America).

Investigation on shed icicle characteristics and induced surface discharges along a suspension insulator string during ice accretion

This investigation focuses on the dynamic process of ice accretion and induced surface discharges along a suspension insulator string in relation with the icicle characteristics in icing conditions. Using a high-speed camera to record the insulator performance, the growth parameters of icicles at different shed edges were calculated and the characteristics of surface discharges were analysed with regards to the lapse time of ice accretion. It was found that the electric field strength can be quickly enhanced to the threshold value of air breakdown strength at the initial stage of ice accumulation, resulting in weak and unstable discharges at the air gaps between the icicles and the insulator shed surface. As the icicle kept elongating toward ice bridging, the discharges became stronger and more stable. The obtained results will be helpful to improve the operating safety of suspension insulators of power networks subjected to icing.

Detailed Analysis of the Far‐Regional Seismic Coda in Kazakhstan Using Array Processing

Abstract An analysis of seismic coda phases recorded by five small aperture arrays in Kazakhstan and Russia is performed. The characteristics of the coda phases are obtained using array processing providing estimates of direction of propagation, frequency content, and apparent propagation velocity of coherent arrivals propagating through the arrays. A statistical analysis, using the coda characteristics of the whole dataset (far‐regional earthquakes) recorded by the arrays, is performed leading to a time‐azimuth distribution of the detected waves. Long Lg ‐coda wavetrains clearly dominate the far‐regional seismic records. The later part of an Lg ‐coda wavefield is generally expected to consist of omnidirectional and multiple scattered waves; still, in the present study, preferential propagation directions of scattered waves are identified in seismic signals, even for a lapse time larger than 1200 s. The comparison of the Lg ‐coda characteristics for two different groups of earthquakes and for the different arrays shows that the geometrical configuration of the event array strongly influences the back‐azimuthal distribution of detected waves. More precisely, temporal variations of the Lg ‐coda characteristics are identified: (1) as a transitory regime in the early part of the coda where arrival directions deviate from the epicenter back azimuth (eastward or westward); (2) as a final regime where the later part of the Lg coda observed by the two northern arrays exhibits incoherent phases with random propagation directions; and (3) as a final regime for the three southern arrays, which reveals coherent arrivals propagating from array‐specific back azimuths not related to the epicenter back azimuth. Electronic Supplement: Figures showing frequency content of detections.

Perioperative factors associated with hidden blood loss in intertrochanteric fracture patients.

The actual total blood loss after a hip fracture has been found to be considerably larger than that observed during surgery and collected in drainage postoperatively. However, no previous studies have offered reasonable explanations for the deficit between a large hemoglobin drop and a small intraoperative blood loss. The aim was to quantify blood loss associated with hip injuries and surgery, and to identify the relative risk factors for perioperative hidden blood loss. Eighty-nine patients with a femoral intertrochanteric fracture were operated on between August 2012 and October 2013. The patients were accepted to undergo DHS (AO/ASIF) surgery or PFN-a (AO/ASIF) surgery and were randomly assigned to one of the two groups according to whether they had a wound drain or not. Admission information collected included: age, gender, body mass index (BMI), the American Society of Anesthetists system (ASA grading), plasma albumin (ALB), specific gravity of urine (SGU), fracture type (FT), surgery type (ST), and time from admission to surgery in hours (TAS). Blood samples for HB (hemoglobin) analysis were obtained upon admission, at 1h preoperatively, and at successive postoperation days. The hidden blood loss was calculated by deducting the observed perioperative blood loss from the calculated total blood loss based on the hematocrit changes. A total of 82 patients with a mean admission lapse time of 4h after injury remained for the final analysis. One-way analysis of variance (ANOVA) of HBL shows the significant difference was observed in BMI subgroups, ALB subgroups, SGU subgroups, and ST subgroups, but no difference was observed in other subgroups. A multivariate linear regression investigating the relationship between HBL and all factors show that decreased albumin at admission and PFN-a surgery were variables associated with increased HBL. Several readily available preoperative factors in the form of non-drainage, BMI<25kg/m2, admission specific gravity of urine >1.020, surgery type PFN-a, and admission albumin <30g/L were associated with a greater likelihood of more HBL. In addition, the latter two are independent risk factors for greater HBL in patients with intertrochanteric fractures.

Is it Justified to use the Lapse Day as a Decision Maker of Laparoscopic Cholecystectomy for Symptomatic Gall Bladder Stone Disease

Aim: Lapse from symptom onset to surgery has been traditionally used for the operation timing of cholecystectomy. However, intraoperative gallbladder (GB) inflammation status has never been studied to verify its justification.Methods: Meticulous intraoperative inflammation status of 260 consecutive laparoscopic cholecystectomy (LC) patients with symptomatic GB stone disease was prospectively graded (I-VI). Inflammation status in terms of lapse, incidence of difficult GB, complication and conversion rate from LC to open cholecystectomy was retrospectively analysed.Results: Various inflammation grades were non-significantly different in each lapse group irrespective of the lapse time. Severity is not always proportionally increased to the lapse time in every patient. One hundred seventeen patients (45%) had inflammations beyond the GB that reached Calot’s triangle or the hepatoduodenal ligament (Grade IV~VI): 64 (54.7%) were Grade V or VI and were defined as difficult GB. There were no statistically significant differences in terms of incidence of difficult GB, or conversion rate between the lapse groups. When divided into any two lapse groups, only the ≤ 3 and >3 days groups showed a significant difference (P=0.039) in the incidence of difficult GB. But the conversion rate was not significantly different (P=0.388).Conclusion: A majority of the patients were easily manageable despite the different lapse times. Less than onethird of the patients with difficult GB needed earlier LC to avert subsequent progression of dense fibrosis if delayed. Dichotomized lapse determination for LC without considering intraoperative inflammation status is not justified.

Geochemistry of speleothems affected by aragonite to calcite recrystallization – Potential inheritance from the precursor mineral

Formerly aragonite speleothems recrystallized to calcite result from solutions subsaturated in aragonite and supersaturated in calcite that infiltrate into the speleothem through the interconnected porosity. In most cases, the crystal replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary calcite crystals record the composition of the fluid at the time of diagenesis affected by calcite partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary calcite that replaced aragonite, although a core of primary aragonite extending 45mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U–Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and calcite sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50±45μm/yr. Such recrystallization rate can transform any aragonite speleothem into calcite within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is of critical importance for inheritance of different elements. The volume of solution is controlled by (1) the discharge of water passing through the sample and (2) the lapse time between aragonite dissolution and calcite precipitation. Hydrology and hydrochemistry of the interacting solution, together with the mineralogy and texture of the speleothem are the essential controls for the diagenesis of the speleothem. Recrystallization of aragonite speleothems does not follow stratigraphical levels of the sample but occurs along sites with preferential flow paths in any sector of the speleothem. In these cases the relationship between age and distance from base is not preserved. However, alternation of periods of recrystallization with periods of aragonite precipitation causing speleothem accretion can result in recrystallized speleothems with coherent distance from the base-age relationship. Thus, early diagenesis of speleothems affected by seasonal or inter-annual oscillation of drip waters supersaturated and subsaturated in aragonite may provide best-scenario conditions for dating and preservation of paleoenvironmental records along recrystallized speleothems. However, even in this scenario, the variable discharge and the diagenetic rate control the geochemical inheritance from the primary aragonite crystals.

Preliminary estimation of high-frequency (4–20 Hz) energy released from the 2016 Kumamoto, Japan, earthquake sequence

We estimate high-frequency (4–20 Hz) energy release due to the 2016 Kumamoto, Japan, earthquake sequence, within a time period from April 14 to 26 through envelope inversion analysis applied to the Hi-net continuous seismograms. We especially focus on energy releases after each of the April 14 M JMA6.5 and the April 16 M JMA7.3 earthquakes. The cumulative energy release from aftershocks of the April 14 event reaches 60% of that from the April 14 event itself by the lapse time of 27 h (pre-April 16 period). On the other hand, the cumulative energy release from aftershocks of the April 16 event reaches only 11 and 13% of that from the April 16 event itself by the lapse times of 27 h and 10 days (post-April 16 period), respectively. This discrepancy in the normalized cumulative energy release (NCER) indicates that the April 14 event was followed by much larger relative aftershock productivity than the April 16 event. Thus, NCER would provide information that reflects relative aftershock productivity and ongoing seismicity pattern after a large earthquake. We also find that the temporal decay of the energy release rate obeys the power law. The exponent p E of the power-law decay is estimated to be 1.7–2.1, which is much larger than the typical p value of the Omori–Utsu law: slightly larger than 1. We propose a simple relationship given by p E = βp/b, where p value, b value of the Gutenberg–Richter law, and β value of the magnitude–energy release relationship are combined.

Body wave attenuation characteristics in the crust of Alborz region and North Central Iran

Attenuation of P and S waves has been investigated in Alborz and north central part of Iran using the data recorded by two permanent and one temporary networks during October 20, 2009, to December 22, 2010. The dataset consists of 14,000 waveforms from 380 local earthquakes (2 < M L < 5.6). The extended coda normalization method (CNM) was used to estimate quality factor of P (Q P) and S waves (Q S) at seven frequency bands (0.375, 0.75, 1.5, 3, 6, 12, 24 Hz). The Q P and Q S values have been estimated at lapse times from 40 to 100 s. It has been observed that the estimated values of Q P and Q S are time independent; therefore, the mean values of Q P and Q S at different lapse times have been considered. The frequency dependence of quality factor was determined by using a power-law relationship. The frequency-dependent relationship for Q P was estimated in the form of (62 ± 7)f (1.03 ± 0.07) and (48 ± 5)f (0.95 ± 0.07) in Alborz region and North Central Iran, respectively. These relations for Q S for Alborz region and North Central Iran have estimated as (83 ± 8)f (0.99 ± 0.07) and (68 ± 5)f (0.96 ± 0.05), respectively. The observed low Q values could be the results of thermoelastic effects and/or existing fracture. The estimated frequency-dependent relationships are comparable with tectonically active regions.

Frequency and lapse time dependent seismic attenuation in eastern Himalaya and southern Tibet

We have studied the attenuation characteristics of eastern Himalaya and southern Tibet by using local earthquake data set that consists of 123 well-located events, recorded by the Himalayan Nepal Tibet Seismic Experiment operated during 2001–2003. We have used single backscattering model to calculate frequency-dependent values of coda Q ( $$Q_\mathrm{c}$$ ). The estimation of $$Q_\mathrm{c}$$ is made at central frequencies 2, 4, 8 and 12 Hz through five lapse time windows from 10 to 50 s starting at double the travel time of the S-wave. The observed $$Q_\mathrm{c}$$ is found to be strongly frequency-dependent and follows a similar trend as observed in other tectonically active parts of the Himalaya. The trend of variation of $$Q_\mathrm{c}$$ with lapse time and the corresponding apparent depths is also studied. Increase in $$Q_\mathrm{c}$$ values with the lapse time suggests that the deeper part of the study region is less heterogeneous than the shallower part. The observed values of $$Q_0$$ ( $$Q_\mathrm{c}$$ at 1 Hz) and frequency parameter n indicate that the medium beneath the study area is highly heterogeneous and tectonically very active. A regionalization of the estimated $$Q_0$$ is carried out, and a contour map is prepared for the whole region. Some segments of Lesser Himalaya and Sub-Himalaya exhibit very low $$Q_0$$ , while the whole Tethyan Himalaya and some parts of Greater Himalaya are characterized by low $$Q_0$$ values. Our results are comparable with those obtained from tectonically active regions in the world.

What should be legal consequences of lapse time of bringing to responsibility for commission of tax offence

What should be legal consequences of lapse time of bringing to responsibility for commission of tax offence

Deriving Sensitivity Kernels of Coda-Wave Travel Times to Velocity Changes Based on the Three-Dimensional Single Isotropic Scattering Model

Recently, coda-wave interferometry has been used to monitor temporal changes in subsurface structures. Seismic velocity changes have been detected by coda-wave interferometry in association with large earthquakes and volcanic eruptions. To constrain the spatial extent of the velocity changes, spatial homogeneity is often assumed. However, it is important to locate the region of the velocity changes correctly to understand physical mechanisms causing them. In this paper, we are concerned with the sensitivity kernels relating travel times of coda waves to velocity changes. In previous studies, sensitivity kernels have been formulated for two-dimensional single scattering and multiple scattering, three-dimensional multiple scattering, and diffusion. In this paper, we formulate and derive analytical expressions of the sensitivity kernels for three-dimensional single-scattering case. These sensitivity kernels show two peaks at both source and receiver locations, which is similar to the previous studies using different scattering models. The two peaks are more pronounced for later lapse time. We validate our formulation by comparing it with finite-difference simulations of acoustic wave propagation. Our formulation enables us to evaluate the sensitivity kernels analytically, which is particularly useful for the analysis of body waves from deeper earthquakes.

Evidence for a fluid flow triggered spatio-temporal migration of seismicity in the 2001 Mw 7.7 Bhuj earthquake region, Gujarat, India, during 2001–2013

We studied the variations in spatial and temporal clustering of earthquake activity (during 2001–2013) in the Kachchh seismic zone, Gujarat, India, by precisely relocating 3478 events using a joint hypocentral determination (JHD) relocation technique, and high-quality arrival times of 21032 P- and 20870 S-waves. Temporal disposition of estimated station corrections of P- and S-waves suggests that the fluid flow in the causative fault zone of the 2001 Bhuj mainshock increased during 2001–2010, while it reduced during 2011–2013, due to the healing process associated with the perturbed Kachchh fault zone. We also estimated the isotropic seismic diffusivities from epicentral growth patterns, which are found to be much lower than those observed for reservoir-induced seismicity sites in the world. Finally, we analysed the spatial and temporal evolution of this earthquake sequence by solving the diffusion equation of pore-pressure relaxation caused by co- and post-seismic stress changes associated with earthquakes. The value of the isotropic diffusivity is estimated to be 100 m2/s for the Kachchh rift zone. This gives a higher permeability (after a lapse time of 14 years from the occurrence of the 2001 Bhuj mainshock) in comparison to those observed for other intraplate regions in the world. Our results suggest that the observed spatio-temporal migration of seismicity is consistent with the shallow (meteoric water circulation at 0–10 km depths) and deeper (metamorphic fluid and volatile CO2 circulation at 10–40 km depths) fluid flows in the permeable and fractured causative fault zone of the 2001 Bhuj earthquake.

Depth‐Dependent Crustal Scattering Attenuation Revealed Using Single or Few Events in South Korea

Few studies have been conducted on the variance of scattering (![Graphic][1] ) and intrinsic attenuation (![Graphic][2] ) with depth in the crust. Furthermore, these values, routinely estimated using multiple lapse time window analysis (MLTWA), were seriously affected by different earthquake depths. Based on earthquakes recorded by dense seismic networks in South Korea, we used the MLTWA method on single or small clusters of events with similar depths. The depths of 54 earthquakes, relocated using seven velocity models, provide a typical seismogenic layer with the brittle–plastic transition (BPT) depth at 11 km, which correlated well with the seismicity of Korea. The depth was also used for the theoretical model based on the direct‐simulation Monte Carlo method. As the result of MLTWA, events with shallow focal depths exhibit higher ![Graphic][3] correlated with dense scatter, whereas those with deeper focal depths exhibit lower ![Graphic][4] . This depth dependency of the ![Graphic][5] value is indicated by the significant difference between the upper and lower parts of the BPT depth in the seismogenic layer. We also found that ![Graphic][6] values do not show depth dependency, whereas ![Graphic][7] values do. Thus, this study demonstrates for the first time that the crustal depth dependency of total (![Graphic][8] ) attenuation originates from ![Graphic][9] rather than from ![Graphic][10] . The approach using single or few events may be helpful for a regional study of ![Graphic][11] and ![Graphic][12] in seismically inactive regions for which insufficient data exist and may provide insight into the seismogenic layer related to potential seismic hazards. Online Material: Tables of residuals and range of multiple lapse time window analysis (MLTWA) parameters and Q −1 values for studied events. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif [7]: /embed/inline-graphic-7.gif [8]: /embed/inline-graphic-8.gif [9]: /embed/inline-graphic-9.gif [10]: /embed/inline-graphic-10.gif [11]: /embed/inline-graphic-11.gif [12]: /embed/inline-graphic-12.gif

The seismic wave absorption in the crust and upper mantle in the vicinity of the Kislovodsk seismic station

The Q-factor estimates of the Earth’s crust and upper mantle as the functions of frequency (Q(f)) are obtained for the seismic S-waves at frequencies up to ~35 Hz. The estimates are based on the data for ~40 earthquakes recorded by the Kislovodsk seismic station since 2000. The magnitudes of these events are M W > 3.8, the sources are located in the depth interval from 1 to 165 km, and the epicentral distances range from ~100 to 300 km. The Q-factor estimates are obtained by the methods developed by Aki and Rautian et al., which employ the suppression of the effects of the source radiation spectrum and local site responses in the S-wave spectra by the coda waves measured at a fixed lapse time (time from the first arrival). The radiation pattern effects are cancelled by averaging over many events whose sources are distributed in a wide azimuthal sector centered at the receiving site. The geometrical spreading was specified in the form of a piecewise-continuous function of distance which behaves as 1/R at the distances from 1 to 50 km from the source, has a plateau at 1/50 in the interval from 50–70 km to 130–150 km, and decays as \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {\sqrt R }}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\sqrt R }$}}\) beyond 130–150 km. For this geometrical spreading model and some of its modifications, the following Q-factor estimates are obtained: Q(f) ~ 85f 0.9 at the frequencies ranging from ~1 to 20 Hz and Q(f) ~ 75f 1.0 at the frequencies ranging from ~1 to 35 Hz.

The Attenuation of High‐Frequency Seismic Waves in the Lower Siang Region of Arunachal Himalaya:Qα,Qβ,Qc,Qi, andQs

In the present study, the scattering and intrinsic attenuation are separated using the S ‐wave attenuation ( Q β ) and coda‐wave attenuation ( Q c ) employing the Wennerberg (1993) method, and the frequency‐dependent Q s and Q i relations have been developed for the region. The Q i and Q s show the frequency‐dependent character in the frequency range 1.5–24 Hz. The average scattering and intrinsic relationships are obtained for the region as Q s =(31±1) f 1.04±0.02, Q s =(48±1) f 1.05±0.02, and Q s =(61±1) f 1.05±0.02 and as Q i =(68±1) f 0.95±0.06, Q i =(134±1) f 1.01±0.05, and Q i =(167±1) f 0.96±0.03 for lapse time windows of 30, 40, and 50 s, respectively. The quality factor for the P wave ( Q α ) and the S wave ( Q β ) are estimated using the extended coda‐normalization method of Yoshimoto et al. (1993). The frequency dependence Q α and Q β relationships are obtained as Q α =(25±1) f (1.24±0.04) for the P wave and Q β =(58±1) f (1.16±0.04) for the S wave. The quality factor for the coda wave ( Q c ) is estimated using the single backscattering model of Aki and Chouet (1975). The comparison of Q β and Q c with Q i and Q s shows that both Q i and Q s are lower than the Q β , as well as Q c , at 30 s lapse time. As the lapse time increases, both Q i and Q s increase in such a manner that Q c will increase because it contains the effects of both. This agrees with the theoretical as well as the laboratory measurements. Also Q c is higher than Q β ; this supports the model given by Zeng et al. (1991), which predicts that the combination of Q i and Q s should be such that Q c is more than Q β .

CodaQin Different Tectonic Areas, Influence of Processing Parameters

Abstract Published results of coda Q show a large variation in values. These variations are often claimed to be related to different tectonics, whereas they might just be related to using different assumptions in the processing, leading to different input parameters for the analysis. In this study, the effect of using different processing parameters is investigated and significant differences, particularly at low frequencies, are observed. We find a new set of optimal parameters, which we recommend using in future studies. Using a short lapse time of 30 s and optimal parameters, data from both similar and very different tectonic regions are used to calculate coda Q using the same program and the same parameters. The regions considered are eastern Anatolia, the Azores, Jan Mayen, northwestern and central Argentina, the Shanxi rift system in China, and southwestern Norway. We obtain the following relations: eastern Anatolia ( Q =88 f 0.66 ), Azores ( Q =86 f 0.70 ), Jan Mayen ( Q =90 f 0.72 ), northwestern and central Argentina ( Q =89 f 0.94 ), Shanxi rift system ( Q =99 f 0.89 ), and southwestern Norway ( Q =124 f 0.91 ). The results show that coda Q is very similar for regions of similar tectonics and significantly different for regions with varying tectonics. Using alternative, more common parameters gives different Q , but the regional differences remain, so which parameters to use to get correct coda Q values is still uncertain. However, coda Q can clearly distinguish different tectonic areas provided identical processing parameters are used, even if they are not optimal.

Attenuation characteristics in eastern Himalaya and southern Tibetan Plateau: An understanding of the physical state of the medium

Attenuation characteristics of the crust in the eastern Himalaya and the southern Tibetan Plateau are investigated using high quality data recorded by Himalayan Nepal Tibet Seismic Experiment (HIMNT) during 2001–2003. The present study aims to provide an attenuation model that can address the physical mechanism governing the attenuation characteristics in the underlying medium. We have studied the Coda wave attenuation (Qc) in the single isotropic scattering model hypothesis, S wave attenuation (Qs) by using the coda normalization method and intrinsic (Qi-1) and scattering (Qsc-1) quality factors by the multiple Lapse Time Window Analysis (MLTWA) method under the assumption of multiple isotropic scattering in a 3-D half space within the frequency range 2–12Hz. All the values of Q exhibit frequency dependent nature for a seismically active area. At all the frequencies intrinsic absorption is predominant compared to scattering attenuation and seismic albedo (B0) are found to be lower than 0.5. The observed discrepancies between the observed and theoretical models can be corroborated by the depth-dependent velocity and attenuation structure as well as the assumption of a uniform distribution of scatterers. Our results correlate well with the existing geo-tectonic model of the area, which may suggest the possible existence of trapped fluids in the crust or its thermal nature. Surprisingly the underlying cause of high attenuation in the crust of eastern Himalaya and southern Tibet makes this region distinct from its adjacent western Himalayan segment. The results are comparable with the other regions reported globally.

Spatial changes of seismic attenuation and multiscale geological heterogeneity in the Baikal rift and surroundings from analysis of coda waves

The Baikal rift system is undergoing an active tectonic deformation expressed by a high level of seismic activity. This deformation leads to physical and mechanical changes of crustal properties which can be investigated by the seismic quality factor and its frequency dependence. Using a single backscattering model, a seismic quality-factor (QC), a frequency parameter (n) and an attenuation coefficient (δ) have been estimated by analyzing coda waves of 274 local earthquakes of the Baikal rift system for nineteen lapse time windows (W) from 10 to 100s every 5s and for six central frequencies (0.3, 0.75, 1.5, 3, 6 and 12Hz). The average QC value increases with the frequency and lapse time window from 46±52 (at 0.75Hz) to 502±109 (at 12Hz) for W=10s and from 114±49 (at 0.3Hz) to 1865±679 (at 12Hz) for W=100s. The values of QC(f) and δ were estimated for the whole Baikal rift system and for separate tectonic blocks: the stable Siberian Platform, main rift basins, spurs and uplifts. Along the rift system, the Q0-value (QC-factor at the frequency f=1Hz) varies within 72–109 and the frequency parameter n ranges from 0.87 to 1.22, whereas Q0 is 134 and n is 0.48 for the stable Siberian Platform. Vertical variations of attenuation reveal that sharp changes of δ and n are confined to the velocity discontinuities. The comparison of lateral variations of seismic wave attenuation and geological and geophysical characteristics of the Baikal rift system shows that attenuation is correlated with both seismic activity and heat flow and in a lesser degree with the surface fault density and the age of the crust. Seismic wave attenuation found across the main shear zones of the south-western Baikal rift (Main Sayan strike-slip fault zone and Tunka, Obruchev and Primorsky normal faults) is increased by more than 25–60% compared to the neighboring areas.

Lapse time dependent coda-Q (Q c) in the Kachchh, rift zone, Gujarat, India

We study the attenuation of seismic wave energy in the aftershock zone of the 2001 Bhuj earthquake using high-quality (S/N ratio ≥ 2.0) data of 181 aftershocks recorded on eleven three-component broadband seismograph stations. The moment magnitudes and focal depths of the selected aftershocks vary from 2.7 to 4.8 and 2 to 50 km, respectively. The three-component broadband data of these selected aftershocks are used to estimate a new frequency-dependent coda-Q (Q c) relation (Q c = Q 0 f n ) in the frequency range 1.5–15 Hz, for the seismically active Kachchh rift zone, Gujarat. We have used single backscattering model to estimate frequency-dependent values of coda Q c at central frequencies 1.5, 3, 6, 9, 12 and 15 Hz through eight lapse time windows (t L) from 20 to 90 s starting at double the travel time of S-waves. The average frequency-dependent Q c relationship in the range of 1.5–15 Hz for the Kachchh region is estimated to be (82 ± 1) f (1.12±0.01), (121 ± 1) f (1.03±0.01), (154 ± 1) f (0.96±0.01), (181 ± 1) f (0.91±0.01), (207 ± 1) f (0.85±0.01), (239 ± 1) f (0.79±0.01), (271 ± 1) f (0.73±0.01) and (304 ± 1) f (0.68±0.01), for lapse time windows of 20, 30, 40, 50, 60 70, 80 and 90 s, respectively. For t L = 20–50 s, we estimate Q c = 52–163 and n = 0.87–1.18, while for t L = 60–90 s, we find Q o = 128–486 and n = 0.45–1.05. These estimates of Q o and n are found to be in good agreement with the estimates of Q o and n for highly heterogeneous and seismically active regions around the world. We also estimate actual hazard parameters, viz. the extinction distances (L e) and anelastic attenuation coefficients (γ), by assuming that attenuation is entirely intrinsic. L e estimates vary from 56 to 99 km, while the corresponding γ estimates range from 0.009 to 0.0054 km−1. The estimated Q o values at locations in the Mesozoic Kachchh rift basin are found to be low in comparison with the areas at a distance from it. This could be attributed to the fact that seismic waves being highly scattered for paths through the seismically active and fractured zone, but less scattered outside the aftershock zone. This model also gets support from the presence of 1- to 2-km-thick top low-velocity Quaternary sediments, and a large volume of crustal and upper mantle metamorphic fluids/carbonatite melts underlying the central rift basin. We also propose that the Q c relations developed in this study could be useful for predicting ground motion in the region.

Frequency dependent attenuation characteristics of coda waves in the Northwestern Himalayan (India) region

Digital seismogram data of 82 earthquakes from the Northwestern Himalayan (India) region recorded at different stations during 2004–2006 were analyzed to study the seismic coda wave attenuation characteristics in this region. We used 132 seismic observations from local earthquakes with a hypocentral distance <240km and a magnitude range of 1.2–4.9 to study the coda QC using the single isotropic scattering model. These earthquakes were recorded at 20 temporary seismic stations installed in the Northwestern Himalayas (India) by the Wadia institute of Himalayan Geology, Dehradun. The QC values were estimated at 10 central frequencies: 1.5, 3, 5, 7, 9, 12, 16, 20, 24, and 28Hz using starting lapse-times of 10, 20, 30, 40, 50, and 60s and coda window-lengths of 10, 20, 30, 40, and 50s. The QC fits the frequency dependent power-law, QC=Q0fn. For a 10s lapse time with a 10-s coda window length QC=47.42f1.012 and for a 50s lapse time with a 50s coda window length, QC=204.1f0.934. Q0 (QC at 1Hz) varied from ∼47 for a 10s lapse time and a 10s window length, to ∼204 for a 50s lapse time and a 50s window length. An average frequency dependent power law fit for the study region may be given as QC=116.716f0.9943. The exponent of the frequency dependence law n ranged from 1.08 to 0.9, which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world. In our study region, QC increases both with respect to lapse time and frequency, i.e., the attenuation decreases as the quality factor is inversely proportional to attenuation. The low QC values or high attenuation at lower frequencies and high QC values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region.