Upper mantle heterogeneity in the northern part of Eurasia

A two dimensional velocity model of the upper mantle has been compiled from a long-range seismic profile crossing the West Siberian young plate and the old Siberian platform. It revealed considerable horizontal and vertical heterogeneity of the mantle. A sharp seismic boundary at a depth of 400 km outlines the high-velocity gradient transition zone, its base lying at a depth of 650 km. Several layers with different velocities, velocity gradients and wave attenuation are distinguished in the upper mantle. They likewise differ in their inner structure. For instance, the uppermost 50–70 km of the mantle are divided into blocks with velocities from 7.9–8.1 to 8.4–8.6 km s^?1.Comparison of the travel-time curves for the Siberian long-range profile with those compiled from seismological data for Europe distinguished large-scale upper mantle inhomogeneities of the Eurasian continent and allowed for the correlation of tectonic features and geophysical fields. The velocity heterogeneity of the uppermost 50–100 km of the mantle correlates with the platform age and heat flow, i.e., the young plates of Western Europe and Western Siberia have slightly lower velocities and higher heat flows than the ancient East European and Siberian platforms. At greater depths (150–250 km) the upper mantle velocities increase from the ocean to the inner parts of the continent. The structure of the transition zone differs significantly beneath Western Europe and the other parts of Eurasia. The sharp boundary at a depth of 400 km, traced throughout the whole continent as the boundary reflecting intensive waves, transforms beneath Western Europe into a gradient zone. This transition zone feature correlates with positions of the North Atlantic-west Europe geoid and heat-flow anomalies.     

Crustal structure beneath the eastern part of the Coast Ranges (Diablo Range) of central California from explosion seismic and near earthquake data

Seismic refraction and near earthquake data of the U.S. Geological Survey for central California have been compiled into record sections along profiles and interpreted in terms of crustal structure. The profiles are located northeast of the San Andreas fault of central California and run parallel to the general structures. For the explosion seismic line through the centre of the Diablo Range, an uppermost layer (Franciscan formation) with P velocities of 3.6–5.0 km s^?1 decreases in thickness towards the northwest. The lower boundaries of layers with constant velocities of 5.75 and 6.8 km s^?1 are found at almost constant depths of 12 and 21 km, respectively. Between 21 and 26 km depth a well-defined low-velocity zone appears whose velocity is estimated as ～ 5.3 km s^?1 with the aid of a hedgehog inversion and the calculation of amplitudes. This zone is underlain by a layer 3–5 km thick with a velocity of 7.6 km s^?1. The upper-mantle velocity beneath the Moho at 29–30 km depth is 8.2 km s^?1. The near earthquake profiles, located ～ 20 km southwest and parallel to the explosion seismic line, follow more or less the Hayward and Calaveras fault systems. The velocity-depth distribution derived for the earthquake data is very similar to that found beneath the Diablo Range. However, the low-velocity zone at 21–26 km depth does not seem to exist everywhere along the line. The Moho is not disturbed beneath the Calaveras, Hayward and Silver Creek faults; it rises slightly from the Diablo Range towards the southwest.     

Deep structure of the East European platform according to seismic data

The paper presents a review and analysis of new seismic data related to the structure of the mantle beneath the East European platform. Analysis of observations of long-range profiles revealed pronounced differences in the structure of the lower lithosphere beneath the Russian plate and the North Caspian coastal depression. The highest P-velocities found at depths around 100 km are in the range 8.4–8.5 km s^?1. Deep structure of the Baltic shield is different from the structures of both these regions. No evidence of azimuthal anisotropy in the upper mantle was found. A distribution of P-velocity in the upper mantle and in the transition zone consistent with accurate travel-time data was determined. The model involves several zones of small and large positive velocity gradients in the upper mantle, rapid increases of velocity near 400 and 640 km depths and an almost constant positive velocity gradient between the 400 and 640 km discontinuities. The depth of the 640 km discontinuity was determined from observations of waves converted from P to SV in the mantle.     

Q-structure beneath the Tibetan Plateau from the inversion of Love- and Rayleigh-wave attenuation data

The fundamental mode Love and Rayleigh waves generated by ten earthquakes and recorded across the Tibet Plateau, at QUE, LAH, NDI, NIL, KBL, SHL, CHG, SNG and HKG are analysed. Love- and Rayleigh-wave attenuation coefficients are obtained at time periods of 5–120 s using the spectral amplitudes of these waves for 23 different paths. Love wave attenuation coefficient varies from 0.0021 km^?1, at a period of 10 s, to 0.0002 km^?1 at a period of 90 s, attaining two maxima at time periods of 10 and 115 s, and two minima at time periods of 25 and 90 s. The Rayleigh-wave attenuation coefficient also shows a similar trend. The very low value for the dissipation factor, Q_β, obtained in this study suggests high dissipation across the Tibetan paths. Backus-Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q_β^?1 models for the crust and uppermost mantle beneath the Tibetan Plateau. Independent inversion of Love- and Rayleigh-wave attenuation data shows very high attenuation at a depth of ～50–120 km ($\text{Q}{}_{\mathrm{\beta }}\text{? 10}$). The simultaneous inversion of the Love and Rayleigh wave data yields a model which includes alternating regions of high and low Q_β^?1 values. This model also shows a zone of high attenuating material at a depth of ～40–120 km. The very high inferred attenuation at a depth of ～40–120 km supports the hypothesis that the Tibetan Plateau was formed by horizontal compression, and that thickening occurred after the collision of the Indian and Eurasian plates.     

Characteristics of radiation and propagation of seismic waves in the Baikal Rift Zone estimated by simulations of acceleration time histories of the recorded earthquakes

The regularities in the radiation and propagation of seismic waves within the Baikal Rift Zone in Buryatia are studied to estimate the ground motion parameters from the probable future strong earthquakes. The regional parameters of seismic radiation and propagation are estimated by the stochastic simulation (which provides the closest agreement between the calculations and observations) of the acceleration time histories of the earthquakes recorded by the Ulan-Ude seismic station. The acceleration time histories of the strongest earthquakes (M _W ~ 3.4–4.8) that occurred in 2006–2011 at the epicentral distances of ~96–125 km and had source depths of ~8–12 km have been modeled. The calculations are conducted with estimates of the Q-factor which were previously obtained for the region. The frequency-dependent attenuation and geometrical spreading are estimated from the data on the deep structure of the crust and upper mantle (velocity sections) in the Ulan-Ude region, and the parameters determining the wave forms and duration of acceleration time histories are found by fitting. These parameters fairly well describe all the considered earthquakes. The Ulan-Ude station can be considered as the reference bedrock station with minimum local effects. The obtained estimates for the parameters of seismic radiation and propagation can be used for forecasting the ground motion from the future strong earthquakes and for constructing the seismic zoning maps for Buryatia.     

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.     

Attenuation models of the earth

Free oscillation and body wave data are used to construct average Q models for the earth. The data set includes fundamental and overtone observations of the radial, spheroidal and toroidal modes, ScS observations and amplitudes of body waves as a function of distance. The preferred model includes a low-Q zone at both the top and the bottom of the mantle. In these regions the seismic velocities are likely to be frequency dependent in the “seismic” band. Absorption in the mantle is predominantly due to losses in shear. Compressional absorption may be important in the inner core.A grain-boundary relaxation model is proposed that explains the dominance of shear over compressional dissipation, the roughly frequency independent average values for Q and the variation of Q with depth. In the high-Q regions, the lithosphere and the midmantle (200–2000 km), Q is predicted to be frequency dependent. However, the low-Q regions of the earth, where Q is roughly frequency independent, dominate the observations of attenuation.     

The <Emphasis Type="Italic">Q</Emphasis>-factor estimates for the crust and upper mantle in the vicinity of Sochi and Anapa (North Caucasus)

The regularities in the radiation and propagation of seismic waves in the regions of the North Caucasus are analyzed for estimating the ground motion parameters during the probable future strong earthquakes. Based on the records of the regional earthquakes with magnitudes M_W ~ 3.9–5.6 within epicentral distances up to ~300 km obtained during the period of digital measurements at the Sochi and Anapa seismic stations, the Q-factors in the vicinities of these sites are estimated at ~55 f^0.9 and ~90f^0.7, respectively. The estimates were obtained by the coda normalization method developed by Aki, Rautian, and other authors. This method is based on the phenomenon of suppression of the earthquake (source) effects and local (site) responses by coda waves in the S-wave spectra. The obtained Q-factor estimates can be used for forecasting the ground shaking parameters for the future probable strong earthquakes in the North Caucasus in the vicinities of Sochi and Anapa.     

Seismic structure of Iceland from Rayleigh wave inversions and geodynamic implications

We have constrained the shear-wave structure of crust and upper mantle beneath Iceland by analyzing fundamental mode Rayleigh waves recorded at the ICEMELT and HOTSPOT seismic stations in Iceland. The crust varies in thickness from 20 to 28 km in western and northern Iceland and from 26 to 34 km in eastern Iceland. The thickest crust of 34–40 km lies in central Iceland, roughly 100 km west to the current location of the Iceland hotspot. The crust at the hotspot is ∼32 km thick and is underlain by low shear-wave velocities of 4.0–4.1 km/s in the uppermost mantle, indicating that the Moho at the hotspot is probably a weak discontinuity. This low velocity anomaly beneath the hotspot could be associated with partial melting and hot temperature. The lithosphere in Iceland is confined above 60 km and a low velocity zone (LVZ) is imaged at depths of 60 to 120 km. Shear wave velocity in the LVZ is up to 10% lower than a global reference model, indicating the influence of the Mid-Atlantic Ridge and the hotspot in Iceland. The lowest velocities in the LVZ are found beneath the rift zones, suggesting that plume material is channeled along the Mid-Atlantic Ridge. At depths of 100 to 200 km, low velocity anomalies appear at the Tjornes fracture zone to the north of Iceland and beneath the western volcanic zone in southwestern Iceland. Interestingly, a relatively fast anomaly is imaged beneath the hotspot with its center at ∼135 km depth, which could be due to radial anisotropy associated with the strong upwelling within the plume stem or an Mg-enriched mantle residual caused by the extensive extraction of melts.     

Comparison of Sesimic Body Wave and Coda Wave Measures of Q

—Measurements of seismic attenuation (Q ^?1) can vary considerably when made from different parts of seismograms or using different techniques, particularly at high frequencies. These discrepancies may be methodological, or may reflect earth processes. To investigate this problem, we compare body wave with coda Q ^?1 results utilizing three common techniques i) parametric fit to spectral decay, ii) coda normalization of S waves, and iii) coda amplitude decay with lapse time. Q ^?1 is measured from both body and coda waves beneath two mountain ranges and one platform, from recordings made at seismic arrays in the Caucasus and Kopet Dagh over paths ≤ 4° long. If Q is assumed frequency independent, spectral decay fits show Q _s and Q _coda near 700–800 for both mountain paths and near 2100–2200 for platform paths. Similar values are determined with the coda normalization technique. However, frequency-dependent parameterizations fit the data significantly better, with Q _s ?(1 Hz) and Q _coda?(1 Hz) near 200–300 for mountain paths and near 500–600 for platform paths. Lapse decay measurements are close to the frequency-dependent values, showing that both spectral and lapse decay methods can give similar results when Q has comparable parameterizations. Above 6 Hz, coda measurements suggest some enrichment relative to body waves, perhaps due to scattering, but intrinsic absorption appears to dominate at lower frequencies. All approaches show sharp path differences between the Eurasian platform and adjacent mountains, and all are capable of resolving spatial variations in Q.     

Correlation between electrical conductivity and other geophysical parameters

Anomalies of electrical conductivity are considered in relation to other geophysical parameters, such as seismic wave velocity, attenuation, seismicity and density, and to tectonic features. In the case of active subduction zones there appears to be a good correlation between low conductivity and the seismic quality factor Q. Beneath western North America, a conductive zone in the uppermost mantle apparently is controlled by the thickness and severity of the low-velocity layer. Anomalies in conductivity beneath rift valleys can be related to regions of intermediate seismic P-wave velocity, typically about 7.0 km/sec, which is suggestive of partial melting of mantle material. Within the continental crust, anomalies in conductivity are not, in general, thermally controlled, but they can show correlations with seismicity, and may indicate intra-plate boundaries.     

On the Causes of Frequency-Dependent Apparent Seismological Q

Variability of the Earth’s structure makes a first-order impact on attenuation measurements which often does not receive adequate attention. Geometrical spreading (GS) can be used as a simple measure of the effects of such structure. The traditional simplified GS compensation is insufficiently accurate for attenuation measurements, and the residual GS appears as biases in both Q ₀ and η parameters in the frequency-dependent attenuation law Q(f) = Q ₀ f ^η . A new interpretation approach bypassing Q(f) and using the attenuation coefficient χ(f) = γ + πf/Q _e(f) resolves this problem by directly measuring the residual GS, denoted γ, and effective attenuation, Q _e. The approach is illustrated by re-interpreting several published datasets, including nuclear-explosion and local-earthquake codas, Pn, and synthetic 50–300-s surface waves. Some of these examples were key to establishing the Q(f) concept. In all examples considered, χ(f) shows a linear dependence on the frequency, γ ≠ 0, and Q _e can be considered frequency-independent. Short-period crustal body waves are characterized by positive γ _SP values of (0.6–2.0) × 10^?2 s^?1 interpreted as related to the downward upper-crustal reflectivity. Long-period surface waves show negative γ _LP ≈ ?1.9 × 10^?5 s^?1, which could be caused by insufficient modeling accuracy at long periods. The above γ values also provide a simple explanation for the absorption band observed within the Earth. The band is interpreted as apparent and formed by levels of Q _e ≈ 1,100 within the crust decreasing to Q _e ≈ 120 within the uppermost mantle, with frequencies of its flanks corresponding to γ _LP and γ _SP. Therefore, the observed absorption band could be purely geometrical in nature, and relaxation or scattering models may not be necessary for explaining the observed apparent Q(f). Linearity of the attenuation coefficient suggests that at all periods, the attenuation of both Rayleigh and Love waves should be principally accumulated at the sub-crustal depths (~38–100 km).     

Differences in the Crustal and Uppermost Mantle Structure of the Bohemian Massif from Teleseismic Receiver Functions

A target of our study was the Bohemian Massif in Central Europe that was emplaced during the Variscan orogeny. We used teleseismic records from ten broadband stations lying within and around the massif. Different techniques of receiver function interpretation were applied, including 1-D inversion of R- and Q-components, forward modelling of V _s velocity, and simultaneous determination of Moho depth and Poissons ratio in the crust. These results provide new, independent information about the distribution of S wave velocity down to about 60 km depth. In the area of Bohemian Massif, the crustal thickness varies from 29 km in the NW to 40 km in the SE. A relatively simple velocity structure with gradually increasing velocities in the crust and uppermost mantle is observed in the eastern part of the Bohemian Massif. The western part of the massif is characterized by more complicated structure with low S wave velocities in the upper crust, as well as in the uppermost mantle. This could be related to tectono-magmatic activity in the Eger rift that started in the uppermost Cretaceous and was active in the West Bohemia-Vogland area till the late Cenozoic.     

Preliminary reference Earth model

A large data set consisting of about 1000 normal mode periods, 500 summary travel time observations, 100 normal mode Q values, mass and moment of inertia have been inverted to obtain the radial distribution of elastic properties, Q values and density in the Earth's interior. The data set was supplemented with a special study of 12 years of ISC phase data which yielded an additional 1.75 × 10⁶ travel time observations for P and S waves. In order to obtain satisfactory agreement with the entire data set we were required to take into account anelastic dispersion. The introduction of transverse isotropy into the outer 220 km of the mantle was required in order to satisfy the shorter period fundamental toroidal and spheroidal modes. This anisotropy also improved the fit of the larger data set. The horizontal and vertical velocities in the upper mantle differ by 2–4%, both for P and S waves. The mantle below 220 km is not required to be anisotropic. Mantle Rayleigh waves are surprisingly sensitive to compressional velocity in the upper mantle. High S_n velocities, low P_n velocities and a pronounced low-velocity zone are features of most global inversion models that are suppressed when anisotropy is allowed for in the inversion.The Preliminary Reference Earth Model, PREM, and auxiliary tables showing fits to the data are presented.     

Elasticity of antigorite,seismic detection of serpentinites,and anisotropy in subduction zones

Serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones. Seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites, which thus far has not been possible in the absence of single-crystal elastic properties of antigorite. The elastic constants of antigorite, the dominant serpentine at high-pressure in subduction zones, were measured using Brillouin spectroscopy under ambient conditions. In addition, antigorite lattice preferred orientations (LPO) were determined using an electron back-scattering diffraction (EBSD) technique. Isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography. The isotropic V_P/V_S ratio is 1.76 in the Voigt–Reuss–Hill average, not very different from that of 1.73 in peridotite, but may vary between 1.70 and 1.86 between the Voigt and Reuss bonds. Antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions. V_P varies between 8.9 km s^? 1 and 5.6 km s^? 1 (46% anisotropy), and 8.3 km s^? 1 and 5.8 km s^? 1 (37%), and V_S between 5.1 km s^? 1 and 2.5 km s^? 1 (66%), and 4.7 km s^? 1 and 2.9 km s^? 1 (50%) for the single-crystal and aggregate, respectively. The V_P/V_S ratio and shear wave splitting also vary with orientation between 1.2 and 3.4, and 1.3 and 2.8 for the single-crystal and aggregate, respectively. Thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation. These properties can be used to detect serpentinite, quantify the amount of serpentinization, and to discuss relationships between seismic anisotropy and deformation in the mantle wedge. Regions of high V_P/V_S ratios and extremely low velocities in the mantle wedge of subduction zones (down to about 6 and 3 km.s^?1 for V_P and V_S, respectively) are difficult to explain without strong preferred orientation of serpentine. Local variations of anisotropy may result from kilometer-scale folding of serpentinites. Shear wave splittings up to 1–1.5 s can be explained with moderately thick (10–20 km) serpentinite bodies.     

Great-circle Rayleigh wave attenuation and group velocity,Part IV: Regionalization and pure-path models for shear velocity and attenuation

Pure-path averages for group velocities and specific attenuation have been calculated from individual observations and from path averages for two regionalizations; one original to this study and the other previously devised by Wu. Both are based on four upper-mantle provinces: ocean basin, continent, island arc and mid-ocean ridge. Pure-path group velocities and specific attenuation have also been calculated for combinations of regions and provide well separated regional measurements for such composite regions.Shear-velocity models for pure and combined regions have been derived by a controlled Monte Carlo inversion procedure and indicates that a low-velocity zone is required beneath the oceans, but is not required beneath continents. Models have been produced for pure and combined ocean, ocean-ridge, continent and continent-arc provinces.Q^?1_R determined from pure-path average group velocities and attenuation coefficients has been regionalized successfully for 2- and 3-region combinations. The resulting pure-path Q^?1_R for continents is much lower than that for ocean basins and ocean-ridge provinces. Inversion of Q^?1_R for ocean-ridge provinces shows that the average Q_β for the upper 200 km of these regions is between 85 and 100.     

Structure of the crust and upper mantle beneath Australia from Rayleigh- and Love-wave observations

Fundamental and first higher modes of the Rayleigh- and Love-wave group velocities along seven paths in Australia were jointly inverted by a controlled Monte Carlo procedure to obtain regional shear-wave velocity structures of the crust and upper mantle. Our data support the results of Gonez and Cleary which show an S-wave low velocity zone centred near 110 km depth in eastern Australia. However, the thickness-velocity contrast of the low velocity zone is significantly smaller. The crustal models for eastern Australia are characterized by upper crusts which are both thicker and have lower velocities than those in western Australia and have a less sharp crust-upper mantle boundary. The S-wave velocities for the upper mantle appear to be similar (～ 4.55 km s^?1) throughout the continent, with no obvious dependence on the age of cratonization or crustal thickness.     

Thermal structure and thickness of the lithospheric mantle underlying the Siberian Craton from the kraton and kimberlit superlong seismic profiles

A self-consistent approach is proposed for the investigation of the thermal conditions, chemical composition, and internal structure of the upper mantle of the Earth. Using this approach, the thermal state of the lithospheric mantle beneath the Siberian Craton (SC) is reconstructed from P velocities, taking into account the phase transitions, anharmonicity, and the effects of anelasticity. The velocities of seismic waves are more sensitive to temperature than to the composition of the mantle rocks, which allows the velocity models to be effectively used for reconstruction of the thermal regime of the mantle. The temperature at depths 100–300 km is reconstructed by inversion of the Kraton and Kimberlit superlong seismic profiles for compositions of the garnet harzburgite, lherzolite, and intermediate composition of garnet peridotite. The averaged temperature in the normal continental mantle is reconstructed by inversion of the IASP91 reference model for depleted and fertile substance. One-dimensional models and two-dimensional thermal fields undergo a substantial fall in temperature (～300–600°C) beneath the Siberian Craton as compared to the temperatures of the continental mantle and paleotemperatures inferred from the thermobarometry of xenoliths. Temperature profiles of the Siberian Craton deduced from seismic data lie between the conductive geotherms of 32.5–40.0 mW/m² and below the P(H)-T values obtained for low- and high-temperature xenoliths from the Mir, Udachnaya, and Obnazhennaya kimberlite pipes. The thickness of the thermal lithosphere estimated from the intersection with the potential adiabat is 300–320 km, which is consistent with the data on heat flows and seismotomographic observations. This provides grounds for the assumption that the low-temperature anomalies (thermal roots of continents) penetrate down to a depth of 300 km. The analysis of the sensitivity of seismic velocity and density to the variations in temperature, pressure, and chemical and phase composition of petrological models shows that recognition of fine differences in chemical composition of the lithospheric rocks by seismic methods is impossible.     

Seismic Velocity and Q Structure of the Middle Eastern Crust and Upper Mantle from Surface-wave Dispersion and Attenuation

—Observed velocities and attenuation of fundamental-mode Rayleigh waves in the period range 7–82 sec were inverted for shear-wave velocity and shear-wave Q structure in the Middle East using a two-station method. Additional information on Q structure variation within each region was obtained by studying amplitude spectra of fundamental-mode and higher-mode Rayleigh waves. We obtained models for the Turkish and Iranian Plateaus (Region 1), areas surrounding and including the Black and Caspian Seas (Region 2), and the Arabian Peninsula (Region 3). The effect of continent-ocean boundaries and mixed paths in Region 2 may lead to unrealistic features in the models obtained there. At lower crustal and upper-mantle depths, shear velocities are similar in all three regions. Shear velocities vary significantly in the uppermost 10 km of the crust, being 3.21, 2.85, and 3.39 km/s for Regions 1, 2, and 3, respectively. Q models obtained from an inversion of interstation attenuation data show that crustal shear-wave Q is highest in Region 3 and lowest in Region 1. Q’s for the upper 10 km of the crust are 63, 71, and 201 for Regions 1, 2, and 3, respectively. Crustal Q’s at 30 km depth for the three regions are about 51, 71, and 134. The lower crustal Q values contrast sharply with results from stable continental regions where shear-wave Q may reach one thousand or more. These low values may indicate that fluids reside in faults, cracks, and permeable rock at lower crustal, as well as upper crustal depths due to convergence and intense deformation at all depths in the Middle Eastern crust.