Qs Values Research Articles

A Comprehensive Analysis of Attenuation Characteristics Using Strong Ground Motion Records for the Central Seismic Gap Himalayan Region, India

ABSTRACT This study aims to estimate attenuation characteristics of the central Himalayan region of India concerning various strong-motion parameters such as Kappa value (κ) and site effects. We have tried to elaborate on the regional structural heterogeneities and their implications towards the seismic hazard assessment of the study region. A total of 81 earthquakes recorded at 50 stations situated in the central Himalayan region of India are used for the purpose. The particular focus is kept on Kappa value, which shows variability from 0.03 s to 0.095 s, inferring the higher values obtained in plains with deep sediment accumulations proving high-frequency energy dissipation and stiff-soil/rocky sites exhibit comparatively limited attenuation accordingly. To substantiate these results various attenuation parameters such as coda wave quality factor (Qc), intrinsic attenuation parameter (Qi), and scattering attenuation parameter (Qs), have been estimated for two regions in the central seismic gap Himalayan region of India employing the single backscattering model and Wennerberg formulation. The estimated values of Qc, Qi, and Qs are found to be highly dependent on frequency in the frequency range 1.5–24 Hz for both the regions. The average frequency-dependent relationships () estimated for both regions are and , respectively. The low value of Q0 shows that the region is highly heterogeneous while the higher value of η indicates higher seismicity in the area. It is also found that intrinsic attenuation is predominant over the scattering attenuation, envisaging the behavior of the wave attenuation through the absorption within the granitic layer at shallow depths. At lower frequencies, Qc values are found close to Qs values, which is in agreement with the theoretical measurements suggesting the presence of complex crustal heterogeneities beneath the region affecting the propagation of seismic waves experiencing considerable decay of energy through scattering. To confirm the aggregate attenuation on the stations, the site characteristics are also determined for examining the behavior of the amplification as the ground motion is comprised of the combined effect of the source, path, and site. The sites are amplified at a predominant frequency ( fpeak ) in between 1.5 to 10 Hz for the central Himalayan region. The different attenuation and amplification parameters like kappa, Q, and site effects can be utilized for detailed seismic hazard analysis (based on ground motion prediction equations) of the area as this region is of great importance from a socio-economic point of view.

Attenuation of High-Frequency P and S Waves in the Crust of Central and Western Tien Shan

In order to better understand the attenuation characteristics in the crust of the central and western Tien Shan orogenic belt, we investigate both Qp and Qs values by applying the extended coda-normalization method. We estimate the frequency-dependent attenuation of both P and S waves in the frequency band of 1.0–20.0 Hz using data from local networks. The average frequency relations of Qp and Qs have been derived as Qp = (61 ± 9) × f(1.21±0.08) and Qs = (77 ± 6) × f(1.11±0.04) by fitting a power-law frequency dependence model for the study region. The low Q0 and high η values indicate that the central and western Tien Shan is a tectonically and seismically active region. We also find lateral variations of both Qp,s and Qs/Qp values, reflecting complex tectonic structures in the study area. In general, the relatively high-attenuation areas corresponding to tectonically active regions are found beneath mountainous ranges in the central Tien Shan whereas the relatively low-attenuation areas are associated with stable regions, such as Fergana Basin and Issyk-Kul Lake. Besides, regions in the central Tien Shan with Qs/Qp > 1 are likely partially saturated with fluids or rich in scattering heterogeneities, whereas regions in the western Tien Shan display Qs/Qp < 1, possibly suggesting almost complete fluid saturation.

Estimation of the quality factor based on the microseismicity recordings from Northern Poland

We use the peak frequency method to estimate effective P- and S-wave quality factors (QP and QS) based on the recorded waveforms of microseismic events. We analyze downhole datasets recorded during the hydraulic stimulation of the two unconventional gas reservoirs located in the northern part of Poland. The effective attenuation is lower in the deeper reservoir consistent with higher compaction. In both cases, we observe high QS values relative to QP which is consistent with attenuation coefficients of saturated reservoirs.

Evaluation of surface shortwave and longwave downwelling radiations over the global tropical oceans

In the present study, daily downwelling shortwave (QS) and longwave radiation (QL) data from one satellite and two hybrid products have been evaluated using Global Tropical Moored Buoy Array during 2001–2009 in the tropical oceans. Daily satellite data are used from the Clouds and Earth’s Radiant Energy System (CERES) program. Data are obtained using Moderate Resolution Imaging Spectroradiometer (MODIS) (CM) aboard the Terra and Aqua satellites. Coordinated Ocean Research Experiments (CORE-II) and Tropical Flux data (TropFlux) are the other two hybrid products used in this study. The analysis shows that majority of QS observations as well as derived products lie in 200–300 Wm−2 range in all the three tropical oceans. Both QS and QL in all products overestimated the majority of the observations. Yet, they underestimated the lower (0–100 Wm−2) values in QS and higher (300–440 Wm−2) values in QL. Majority of the QL observations lie within 390–420 Wm−2 range, and CM slightly overestimated this observed distribution in the Pacific and the Atlantic Oceans. But, majority of the observations in the Indian Ocean lie within 420–450 Wm−2 range. This implies that the tropical Indian Ocean receives 30 Wm−2 more energy as compared to the tropical Pacific and the Atlantic in the form of downwelling longwave radiation. Daily observed QS shows dominant seasonal cycle over the central, the eastern Pacific and the eastern Atlantic. On the other hand, the western Pacific, the central Atlantic and the Indian Oceans show intraseasonal variations. All products show this variation with high root-mean-square error (RMSE) values (QS and QL) over the Indian Ocean than in the Pacific and the Atlantic Oceans. Downwelling radiation from CORE-II shows highest RMSE (for both QS and QL) with least correlation coefficient (CC), and TropFlux has lowest RMSE and highest CC among all products in all three tropical oceans. CM has intermediate values of standard deviation, CC and RMSE. These results are not seasonally dependent, since the seasonal statistics are consistent with seasonal changes. Assuming that the SST is only driven by the downwelling shortwave and longwave fluxes, the errors associated with monthly SST can be as large as 0.2–0.3 (0.1–0.2) °C associated with errors in QS (QL). Both QS and QL in CORE-II have lower spatial variability as compared to other datasets. QL in the tropical oceans shows seasonal spatial variability determined by intertropical convergence zone positions. This variability does not change significantly over the Pacific and the Atlantic Oceans. The summer and winter monsoon patterns in the Indian Ocean guide the QL variability. Opposite to QS, higher QL values have lower variability. Thus, this study aims at finding better radiation dataset to use in the numerical models and deduce that satellite data could be an alternative to existing reanalysis products.

Updated attenuation tomography of Japan subduction zone

SUMMARYWe determine an updated model of P- and S-wave attenuation (Qp, Qs) tomography of the Japan subduction zone using an improved inversion scheme, and derive the first Qp/Qs model of the study region. We establish a system of observation t* equations by taking 1/Q values at 3-D grid nodes arranged in the study volume as unknown parameters. This scheme can eliminate model errors caused by ignoring high-order terms of the Taylor expansion in the Q-format scheme adopted by previous studies. The inversion problem is considered as a quadratic programming problem with bound constraints for best fitting the observed t* data in a least-squares sense. The 3-D attenuation model is obtained by using a limited-memory Broyden–Fletcher–Goldfarb–Shanno algorithm for bound constrained optimization. Because this inversion scheme uses bound constraints to avoid negative Q values, damping regularization is not needed, hence the ranges of Qp and Qs values obtained are less affected by human subjectivity. The subducting Pacific and Philippine Sea slabs exhibit high-Q and high Qp/Qs, whereas the mantle wedge beneath the volcanic front and back-arc area shows low-Q and low Qp/Qs. Both Qp and Qs vary in a range of 10–2000, and the Qp/Qs ratio changes from 0.4 to 1.4. Our results reveal a narrow high-Qp/Qs belt that is coincident with the distribution of volcanic and non-volcanic low-frequency micro-earthquakes (M 0.0–2.5), which may reflect high water-saturation anomalies that are probably associated with slab-derived fluids and responsible for the generation of low-frequency micro-earthquakes.

Comparison of time-domain SH waveform inversion strategies based on sequential low and bandpass filtered data for improved resolution in near-surface prospecting

The full waveform inversion (FWI) of strongly dispersive Love wave data is a challenging task. Amplitude, phase and dispersion information not only depends on the density and shear modulus distribution in the subsurface, but also significantly on intrinsic damping. This is especially a problem in near surface data applications with complex underground structures and low Qs values. Therefore, the FWI of a dispersive Love wavefield demands an accurate initial visco-elastic model and careful data pre-processing. Another key ingredient of a successful time-domain FWI is the sequential inversion of frequency filtered data in order to mitigate the non-linearity of the inverse problem. Common FWI strategies are based solely on either low- or bandpass filtered data. In this study we develop an FWI workflow consisting of a combined low- and bandpass filter strategy to achieve an appropriate data fit of the low-frequency Love wave and high-frequency refracted SH-wavefield. The applicability of this FWI strategy and the importance of a visco-elastic medium description is demonstrated for SH field data from a transect over the Fossa Carolina, a silted medieval canal structure in southern Germany. The resolved canal shape and small scale structures in the inversion results are verified by an archaeological excavation.

Assessing LNRF, FR, and AHP models in landslide susceptibility mapping index: a comparative study of Nojian watershed in Lorestan province, Iran

Landslides and slope instabilities are major risks for human activities which often lead to economic losses and human fatalities all over the world. The main purpose of this study is to evaluate and compare the results of Landslide Nominal Risk Factor (LNRF), Frequency Ratio (FR), and Analytical Hierarchy Process (AHP) models in mapping Landslide Susceptibility Index (LSI). The study case, Nojian watershed with an area of 344.91 km2, is located in Lorestan province of Iran. The procedure was as follows: first, the effective factors of the landslide basin were prepared for each layer in the GIS software. Then, the layers and the landslides of the basin were also prepared using aerial photographs, satellite images, and fieldwork. Next, the effective factors of the layers were overlapped with the map of landslide distribution to specify the role of units in such distribution. Finally, nine factors including lithology, slope, aspect, altitude, distance from the fault, distance from river, fault land use, rainfall, and altitude were found to be effective elements in landslide occurrence of the basin. The final maps of LSI were prepared based on seven factors using LNRF, FR, and AHP models in GIS. The index of the quality sum (Qs) was also used to assess the accuracy of the LSI maps. The results of the three models with LNRF (40%), FR (39%), and AHP (44%) indicated that the whole study area was located in the classes of high to very high hazard. The Qs values for the three models above were also found to be 0.51, 0.70 and 0.70, respectively. In comparison, according to the amount of Qs, the results of AHP and FR models have slightly better performed than the LNRF model in determining the LSI maps in the study area. Finally, the study watershed was classified into five classes based on LSI as very low, low, moderate, high, and very high. The landslide susceptibility maps can be helpful to select sites and mitigate landslide hazards in the study area and the regions with similar conditions.

57Fe CEMS study on dilute metal ions codoped SnO2 thin films prepared by spray pyrolysis

Dilute Mn-Fe, Co-Fe and V-Fe codoped tin oxide films prepared by spray pyrolysis were characterized by 57Fe conversion electron Mossbauer spectrometry (CEMS) at room temperature (RT) and at 20 K. Two kinds of paramagnetic Fe3+ species were detected at RT; one doublet 1 (D1) with IS = 0.36–0.37 mm/s, QS = 0.69–0.75 mm/s and LW = 0.32–0.40 mm/s, and another doublet 2 (D2) with IS = 0.31–0.35 mm/s QS = 1.16–1.25 mm/s and LW = 0.46–0.52 mm/s. CEMS at 20 K provided more distinguished doublets than at RT. It is found that especially D2 with relatively small IS and large QS values are influenced by other metal ions codoped in SnO2 matrix, whereas D1 with relatively large IS and small QS has the parameters close to the models of Fe-VO1 and Fe-2VO1-Fe models (Nomura et al. Phys. Rev. B 75, 184411 2007; Mudarra Navarro et al. J. Phys. Chem. C 119, 5596–5603 2015).

The performance evaluation of information value, density area, LNRF, and frequency ratio methods for landslide zonation at Miandarband area, Kermanshah Province, Iran

Landslide is one of the natural disasters which causes a lot of annual damage directly or indirectly in the world. Many planned areas, especially in hilly regions, are prone to different types of landslides; therefore, landslide susceptibility maps become an urgent issue, so that landslide damages and impact can be minimized. The best method for studying landslides, which has long been of interest to researchers, is hazard zonation. In this method, due to the affecting factors in landslide occurrence, study areas are classified into areas with low to very high risk. Different methods have been developed for this purpose. In this paper, the four bivariate statistical methods namely information value, density area, LNRF, and frequency ratio are used to investigate the hazard zonation of landslide in Miandarband located north of the Kermanshah Province. The density ratio (D r) and Qs values for information value, density area, frequency ratio, and LNRF methods used in this study were calculated to be 2.245312, 0.98146; 2.857816, 1.071185; 2.858085, 0.783945; and 2.418375, 1.070928, respectively. The results indicate that although there are minor differences, the frequency ratio method compared to the density area method that was used for the study of landslide zonation presents better results.

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

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

Attenuation Characteristics of High Frequency Seismic Waves in Southern India

We present a systematic study of seismic attenuation and its related Q structure derived from the spectral analysis of P-, S-waves in the southern India. The study region is separated into parts of EDC (Eastern Dharwar Craton), Western Dharwar Craton (WDC) and Southern Granulite Terrain (SGT). The study is carried out in the frequency range 1–20 Hz, using a single-station spectral ratio technique. We make use of about 45 earthquakes, recorded in a network of about 32 broadband 3-component seismograph-stations, having magnitudes (M L) varying from 1.6 to 4.5, to estimate the average seismic body wave attenuation quality factors; Q P and Q S. Their estimated average values are observed to be fitting to the power law form of Q = Q 0 f n . The averaged power law relations for Southern Indian region (as a whole) are obtained as Q P = (95 ± 1.12)f (1.32±0.01); Q S = (128 ± 1.84)f (1.49±0.01). Based on the stations and recorded local earthquakes, for parts of EDC, WDC and SGT, the average power law estimates are obtained as: Q P = (97 ± 5)f (1.40±0.03), Q S = (116 ± 1.5)f (1.48±0.01) for EDC region; Q P = (130 ± 7)f (1.20±0.03), Q S = (103 ± 3)f (1.49±0.02) for WDC region; Q P = (68 ± 2)f (1.4±0.02), Q S = (152 ± 6)f (1.48±0.02) for SGT region. These estimates are weighed against coda Q (Q C) estimates, using the coda decay technique, which is based on a weak backscattering of S-waves. A major observation in the study of body wave analysis is the low body wave Q (Q 0 0.5) and Q S/Q P ≫ 1, suggesting lateral stretches of dominant scattering mode of seismic wave propagation. This primarily could be attributed to possible thermal anomalies and spread of partially fluid-saturated rock-masses in the crust and upper mantle of the southern Indian region, which, however, needs further laboratory studies. Such physical conditions might partly be correlated to the active seismicity and intraplate tectonism, especially in SGT and EDC regions, as per the observed low-Q P and Q S values. Additionally, the enrichment of coda waves and significance of scattering mechanisms is evidenced in our observation of Q C > Q S estimates. Lapse time study shows Q C values increasing with lapse time. High Q C values at 40 s lapse times in WDC indicate that it may be a relatively stable region. In the absence of detailed body wave attenuation studies in this region, the frequency dependent Q relationships developed here are useful for the estimation of earthquake source parameters of the region. Also, these relations may be used for the simulation of earthquake strong ground motions which are required for the estimation of seismic hazard, geotechnical and retrofitting analysis of critical structures in the region.

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.

Soil water infiltration affected by topsoil thickness in row crop and switchgrass production systems

Conversion of annual grain crop systems to biofuel production systems can restore soil hydrologic function; however, information on these effects is limited. Hence, the objective of this study was to evaluate the influence of topsoil thickness on water infiltration in claypan soils for grain and switchgrass (Panicum virgatum L.) production systems. The experiment was performed at the University of Missouri South Farm (38°54′N, 92°16′W) on a Mexico silt loam (Vertic Luvisols) soil. Since 2009, plots were planted with either switchgrass or a corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotation. Infiltration rates were measured using ponded infiltrometers during two years (2014 and 2015) under switchgrass and grain crop management each with two levels of topsoil thickness (0 and 37.5cm). Physically-based Parlange and Green-Ampt infiltration models were used to estimate saturated hydraulic conductivity (Ks) and sorptivity (S) parameters. Switchgrass planted on degraded soil (shallow topsoil treatment) resulted in greater Ks, S, qs (quasi-steady infiltration rate) and Kfs (field-saturated hydraulic conductivity) values than with row crop management for both 2014 and 2015 measurement years. Results for selected 24-hour mean frequency (11.8, 14.2, and 16.2cm) storms showed that switchgrass production systems enhanced estimated water infiltration, reduced estimated runoff, and decreased estimated time from water ponding to end of ponding compared with row crop management. Switchgrass is recommended to be planted on degraded soils especially in claypan landscapes for improved water use.

Semiquantitative immunohistochemistry for mucin (MUC1, MUC2, MUC3, MUC4, MUC5AC, and MUC6) profiling of pancreatic ductal cell adenocarcinoma improves diagnostic and prognostic performance.

Mucin (MUC) glycoproteins are involved in various steps of the carcinogenesis and progression of human malignancies. The aim of this study was to verify whether semiquantitative evaluation of MUC staining by immunohistochemistry may help to differentiate pancreatic ductal cell adenocarcinoma (PDAC) from chronic pancreatitis and normal pancreas. Mucin expression was examined by immunohistochemistry in surgical specimens resected from 101 patients with PDAC and 33 with chronic pancreatitis, and in 40 normal pancreatic tissue specimens. A quickscore (QS, range 0-300) was calculated by multiplying staining intensity by the percentage of positive cells. A diagnostic model was developed for MUC QS (MUC1, MUC2, MUC3, MUC4, MUC5AC, and MUC6), based on a receiver operating characteristic (ROC) curve and logistic regression analysis. Median QS values for MUC1 and MUC5AC were significantly higher for PDAC, whereas patients with non-malignant tissues had higher values for MUC3 and MUC6. The area under the curve for the ROC curve derived from the diagnostic model including MUC3, MUC5AC and MUC6 was 0.96 [95% confidence interval (CI) 0.91-0.98], with 85% sensitivity and 94% specificity. Median QS values for MUC2 were significantly higher in patients with less advanced tumours, whereas venous invasion was associated with a lower QS for MUC6. Moreover, multivariate survival analysis revealed that low MUC6 expression was a negative prognostic factor, with a hazard ratio of 1.73 (95% CI 1.07-2.81). The three-MUC diagnostic model (MUC3, MUC5AC, and MUC6) showed an excellent ability to discriminate pancreatic cancer from non-malignant tissues, and yielded information that may prove useful for the development of clinical applications.

A practical approach for the calculation of the activation energy of the sintering

Newly developed software for calculation of activation energy (Qs in the following) of sintering using the Wang and Raj model is presented. To demonstrate the practical potential of the software and to evaluate the behaviour of the Qs during the sintering process, alumina and cubic zirconia ceramic compacts were prepared from nanometric powders. The results obtained with both materials are in agreement with previously published data calculated by different approaches. In the interval of interest (relative densities from 60 % to almost 100 % of theoretical density), both materials show similar behaviour. Three distinct regions can be seen: the initial constant values of Qs 868 kJ/mol and 762 kJ/mol for alumina and cubic zirconia, respectively; a region containing linear drop of Qs and the final region of constant Qs values 625 kJ/mol and 645 kJ/mol for alumina and cubic zirconia, respectively.

Surface heat flow and lithosphere thermal structure of the Rhenohercynian Zone in the greater Luxembourg region

Comprehensive knowledge of surface heat flow and subsurface temperature distribution is indispensable for the interpretation and quantification of crustal/mantle processes as well as for the evaluation of the geothermal potential of an area. In cases where subsurface temperature data are sparse, thermal modeling may be used as a tool for inferring the geothermal resource at depth but requires profound structural, geological, and petrophysical input data. The study area encompasses the Trier–Luxembourg Basin and the western realm of the Rhenish Massif, itself subdivided into the Ardennes region in the west as well as the Eifel and Hunsrück regions in the east. For the study area, 2-D steady-state and conductive thermal models were established based on geological models of lithosphere-scale which were parameterized using thermal rock properties including thermal conductivity, radiogenic heat production, and density. The thermal models are constrained by surface heat flow (qs) and the geophysically-estimated depth of the lithosphere–asthenosphere boundary (LAB). A qs of 75±7 (2σ)mWm−2 was determined in the area. A LAB depth of 100km, as seismically derived for the Ardennes, provides the best fit with the measured qs. Modeled temperatures are in the range of 120–125°C at 5km depth and of 600–650°C at the Moho, respectively. The mantle heat flow amounts to ∼40mWm−2. Possible thermal consequences of the 10–20Ma old Eifel plume, which caused elevation of the LAB to 50–60km depth, were modeled in a steady-state thermal scenario resulting in a qs of 91mWm−2 in the Eifel region. Available qs values (65–80mWm−2) are significantly lower and do indicate that the plume-related heating has not yet reached the surface in its entirety.

Analysis of diagnostic climate model cloud parametrizations using large‐eddy simulations

Current climate models often predict fractional cloud cover on the basis of a diagnostic probability density function (PDF) describing the subgrid‐scale variability of the total water specific humidity, qt, favouring schemes with limited complexity. Standard shapes are uniform or triangular PDFs, the widths of which are assumed to scale with the grid‐box mean qt or the grid‐box mean saturation specific humidity, qs. In this study, the qt variability is analysed from large‐eddy simulations for two stratocumulus, two shallow cumulus, and one deep convective cases. We find that, in most cases, triangles are a better approximation to the simulated PDFs than uniform distributions. In 2 of the 24 slices examined, the actual distributions were so strongly skewed that the simple symmetric shapes could not capture the PDF at all. The distribution width for either shape scales acceptably well with both the mean values of qt and qs, the former being a slightly better choice. The qt variance is underestimated by the fitted PDFs, but overestimated by the existing parametrizations. While the cloud fraction is in general relatively well diagnosed from fitted or parametrized uniform or triangular PDFs, it fails to capture cases with small partial cloudiness, and in 10–30% of the cases misdiagnoses clouds in clear skies or vice versa. The results suggest choosing a parametrization with a triangular shape, where the distribution width would scale with the grid‐box mean qt using a scaling factor of 0.076. However, this is subject to the caveat that the reference simulations examined here were partly for rather small domains and driven by idealised boundary conditions.

Attenuation and velocity structure from diffuse coda waves: Constraints from underground array data

An analysis of coda waves excited in the 0.2–20Hz frequency band and recorded by the underground array Underseis (central Italy) has been performed to constrain both seismic attenuation at regional scale and velocity structure in the Mount Gran Sasso area. Attenuation was estimated with the MLTWA method, and shows a predominance of scattering phenomena over intrinsic absorption. The values of Qi and Qs are compatible with other estimates obtained in similar tectonic environments. Array methods allowed for a detailed study of the propagation characteristics, demonstrating that earthquake coda at frequencies greater than about 6Hz is composed of only body waves. Coherence and spectral characteristics of seismic waves measured along the coda of local and regional earthquakes indicate that the wavefield becomes fully diffuse only in the late coda. The frequency-dependent energy partitioning between horizontal and vertical components has been also estimated and compared with synthetic values computed in a layered half-space under the diffuse field assumption. This comparison confirms that, for frequencies higher than 6Hz, the coda appears as a sum of body waves coming from all directions while, in the low frequency range (0.2–2Hz), the observations can be well explained by a coda wavefield composed of an equipartition mixture of surface and body waves traveling in a multiple-layered medium. A Monte-Carlo inversion has been performed to obtain a set of acceptable velocity models of the upper crust. The present results show that a broadband coda wavefield recorded in an underground environment is useful to constrain both the regional attenuation and the velocity structure of the target area, thereby complementing the results of classical array analysis of the wavefield.

Body Wave Crustal Attenuation Characteristics in the Garhwal Himalaya, India

We estimate frequency-dependent attenuation of P and S waves in Garhwal Himalaya using the extended coda normalization method for the central frequencies 1.5, 2, 3, 4, 6, 8, 10, 12, and 16 Hz, with earthquake hypocentral distance ranging from 27 to 200 km. Forty well-located local earthquake waveforms were used to study the seismic attenuation characteristics of the Garhwal Himalaya, India, as recorded by eight stations operated by Wadia Institute of Himalayan Geology, Dehradun, India, from 2007 to 2012. We find frequency-dependent P and S wave quality factors as defined by the relations Q P = 56 ± 8f 0.91±0.002 and Q S = 151 ± 8f 0.84±0.002 by fitting a power-law frequency dependence model for the estimated values over the whole region. Both the Q P and Q S values indicate strong attenuation in the crust of Garhwal Himalaya. The ratio of Q S/Q P > 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium, playing an important role in seismic wave attenuation in the Himalayan crust.

Assessing seasonal drought stress response in Norway spruce (Picea abies (L.) Karst.) by monitoring stem circumference and sap flow

AbstractSummer drought frequency is expected to increase with climate change in forested regions of Europe. To examine the physiological impacts of low soil moisture on Norway spruce [Picea abies (L.) Karst.], we conducted an irrigation experiment in a Norway spruce‐dominated forest. We monitored sap flow (Qs), stem circumference and soil water potential (Ψw), measured needle water potential (Ψl), and estimated potential evapotranspiration (PET) in control and irrigated plots. Soil water availability influenced the response of Qs to PET and the impact of Qs on maximum daily stem shrinkage (MDS). The positive relationship between Qs and PET was constrained below a threshold Ψw near −0.3 MPa. MDS was higher beyond this threshold, for a given value of Qs. Higher MDS and lower tree water status (ΔW) were observed at low Ψw in control plants, suggesting the lower water potential of stems' conducting tissues. Stem circumference increase (SCI) was 62% lower in control trees following the irrigation treatment. Slight SCI recovery was observed in these trees in response to early autumn rainfall, which caused ΔW to return to its predrought state. The results demonstrate that low water availability not only reduced Qs, ΔW, SCI, Ψl and increased MDS but also altered their mutual relations. Copyright © 2014 John Wiley &amp; Sons, Ltd.