Synthetic Envelopes Research Articles

An envelope-based machine learning workflow for locating earthquakes in the southern Sichuan Basin

The development of machine learning technology enables more robust real-time earthquake monitoring through automated implementations. However, the application of machine learning to earthquake location problems faces challenges in regions with limited available training data. To address the issues of sparse event distribution and inaccurate ground truth in historical seismic datasets, we expand the training dataset by using a large number of synthetic envelopes that closely resemble real data and build an earthquake location model named ENVloc. We propose an envelope-based machine learning workflow for simultaneously determining earthquake location and origin time. The method eliminates the need for phase picking and avoids the accumulation of location errors resulting from inaccurate picking results. In practical application, ENVloc is applied to several data intercepted at different starting points. We take the starting point of the time window corresponding to the highest prediction probability value as the origin time and save the predicted result as the earthquake location. We apply ENVloc to observed data acquired in the southern Sichuan Basin, China, between September 2018 and March 2019. The results show that the average difference with the catalog in latitude, longitude, depth, and origin time is 0.02°, 0.02°, 2 ​km, and 1.25 ​s, respectively. These suggest that our envelope-based method provides an efficient and robust way to locate earthquakes without phase picking, and can be used in earthquake monitoring in near-real time.

Induced Earthquake Source Parameters, Attenuation, and Site Effects From Waveform Envelopes in the Fennoscandian Shield

AbstractWe analyze envelopes of 233 and 22 ML0.0 to ML1.8 earthquakes induced by two geothermal stimulations in the Helsinki, Finland, metropolitan area. We separate source spectra and site terms and determine intrinsic attenuation and the scattering strength of shear waves in the 3–200 Hz frequency range using radiative transfer based synthetic envelopes. Displacement spectra yield scaling relations with a general deviation from self‐similarity, with a stronger albeit more controversial signal from the weaker 2020 stimulation. The 2020 earthquakes also tend to have a smaller local magnitude compared to 2018 earthquakes with the same moment magnitude. We discuss these connections in the context of fluid effects on rupture speed or medium properties. Site terms demonstrate that the spectral amplification relative to two reference borehole sites is not neutral at the other sensors; largest variations are observed at surface stations at frequencies larger than 30 Hz. Intrinsic attenuation is exceptionally low with values down to 2.4 × 10−5 at 20 Hz, which allows the observation of a diffuse reflection at the ∼50 km deep Moho. Scattering strength is in the range of globally observed data with between 10−3 and 10−4. The application of the employed Qopen analysis program to the 2020 data in a retrospective monitoring mode demonstrates its versatility as a seismicity processing tool. The diverse results have implications for scaling relations, hazard assessment and ground motion modeling, and imaging and monitoring using ballistic and scattered wavefields in the crystalline Fennoscandian Shield environment.

Investigating the suitability of synthetic envelopes as an alternative or complement to stone aggregate in clay-textured soils in Ireland

In Ireland, agricultural landscapes dominated by high rainfall and poorly drained soils have high densities of in-field pipe drains surrounded by stone aggregate envelopes. Unlike other countries, there is limited availability and use of synthetic envelopes, and no data exist about their suitability and efficacy in clay-textured soils. Indeed, both aggregate and synthetic envelope based designs have been implemented without knowledge of their suitability or efficacy. Available synthetic envelopes have two configurations: pre-wrapped loose materials and pre-wrapped geotextiles (woven, non-woven, and knitted, with the knitted being the most common in the U.S. and Canada). In total, five configurations (referred to in this paper as ‘treatments’) were examined in this study with a view to ranking them from performance and cost perspectives. The treatments were: a 0.8-mm-thick needle-punched, non-woven geotextile or a 2-mm-thick knitted filter sock wrapped around the drainpipe, with no aggregate (Treatments 1 and 2, respectively); a 0.8-mm-thick needle-punched, non-woven geotextile wrapped around 2–10 mm (D10–D90) stone aggregate (Treatment 3); a 2-mm-thick knitted filter sock wrapped around a drainpipe surrounded by 2-to-10-mm-diameter stone aggregate (0.15 m above pipe, 0.13 m below pipe) (Treatment 4); and a 2-to-10-mm stone aggregate alone (0.15 m above pipe, 0.13 m below pipe) (Treatment 5). The hydraulic and filter performance of Treatments 1 to 4 were compared with Treatment 5. Treatments 3 and 4 were assessed to determine if they improved hydraulic conductivity and filter performance over Treatment 5. Using cumulative discharge and cumulative flow weighted sediment loss (total suspended solids: TSS) as indicators of performance, geotextiles performed poorly from discharge and TSS perspectives. The discharge for Treatment 1 and Treatment 2 was below the discharge observed from the stone aggregate, and cumulative TSS losses were 636% and 709% higher (Treatment 1 and 2, respectively). The discharge from Treatments 3 and 4 was 67% and 134% higher than the stone aggregate, but this produced an increase in cumulative sediment losses. Treatment 5 performed effectively, with a discharge that was higher than that observed in the geotextile treatments (Treatments 1 and 2) but lower than that observed in Treatments 3 and 4. The use of these treatments, either alone or in combination with stone aggregate, is not recommended in the clay-textured soil tested, from both performance and cost perspectives. Therefore, this study recommends that stone aggregates in the optimal size range should be used as drain envelope material in similar textured soils in Ireland.

Field study on the influence of subsurface drainage pipes and envelopes on discharge and salt leaching in arid areas

AbstractThe selection of suitable drainage materials is crucial for the efficient operation of subsurface drainage systems. Previous studies on drainage material selection have focused on anti‐clogging characteristics, and less attention has been given to their effects on the process of soil salt leaching, which is an important consideration in arid and semi‐arid areas. To investigate the influence of subsurface drainage pipes and envelopes on salt leaching and discharge, field leaching experiments under flood irrigation and drip irrigation were conducted in Xinjiang region in China. Results show that the amount of drainage water in treatments that use gravel envelopes is higher than that in treatments that use synthetic envelopes. Meanwhile, the amount of drainage water in treatments that use gravel envelopes decreases the most after 1 year of operation. The synthetic envelope, the interaction between the perforation rate of the drainage pipe and the synthetic envelope significantly influence water and salt discharge. The optimal level of the synthetic envelope used in this study is spun‐bonded non‐woven geotextile, that of the layer number of envelopes is a single layer, and that of the perforation rate of the drainage pipe is 3.0%.

Dynamic-responsive virus-mimetic nanocapsules facilitate protein drug penetration and extracellular-specific unpacking for antitumor treatment.

Protein-based drugs have been demonstrating great potential for the treatment of various diseases, but most of them encounter many difficulties in clinical trials or uses, such as instability, low bioavailability, and poor in vivo efficacy. In this work, we developed virus-mimetic nanocapsules (VMNs) for improving protein systemic delivery and pharmaceutical effects through bioinspired macromolecular and supramolecular engineering. These VMNs possessed hierarchical nanostructures including artificial capsids, encapsulated proteins, and synthetic envelopes. These dynamic-responsive VMNs can harbor protein drugs, resist protein adsorption, target solid tumors, penetrate into deep tissue, and site-specifically unpack protein drugs. Through surmounting the sequential physio-pathological barriers, protein-loaded VMNs successfully maximized the in vitro and in vivo therapeutic efficacy of proteins, giving a promising strategy to address dilemmas on clinical TRAIL therapy. This study is expected to promote in vivo treatment outcomes and clinical transformation of protein drugs.

Investigating the Suitability of Synthetic Envelopes as an Alternative or Compliment to Stone Aggregate in Clay Textured Soils in Ireland

Investigating the Suitability of Synthetic Envelopes as an Alternative or Compliment to Stone Aggregate in Clay Textured Soils in Ireland

Laboratory comparison of clogging in three types of domestic synthetic envelopes installed in clay‐calcareous soils*

AbstractClogging in subsurface drain envelopes is one of the main issues in drainage systems; changing drainpipes needs a large amount of money and can decrease the profitability of the system, so in this study we tried to select the best envelope according to clogging. This study was conducted to evaluate comparatively the performance of three synthetic envelopes (A, B, C) manufactured in Iran by using a physical permeameter model in the laboratory. The selected envelopes were of PP450 synthetic type. Experiments were performed to examine the changes in drain discharge and hydraulic conductivity of the soil–envelope of each permeameter in each of the three envelopes during a period of 2000 h. Experimental results indicated that at a constant water head, reduction of drain discharge was associated with reduction of hydraulic conductivity of the soil–envelope over time. It was due to the movement of soil particles within the envelopes for each discharge until it reached a constant value or the soil–envelope equilibrium. Comparison of results for the applied envelopes showed that envelope A had a better performance than the other two. Envelope A also had 28% higher drainage coefficient than envelope B and 58% higher drainage coefficient than envelope C, so this property can increase drain distances and save costs. The total hydraulic conductivity of envelope A is 6.5 and 5% higher than those of C and B envelopes, respectively. By comparing envelopes B and C we can see that envelope B presented a better function.

Hybrid Broadband Seismograms for Seismic Shaking Scenarios: An Application to the Po Plain Sedimentary Basin (Northern Italy)

The densely populated Po Plain, a very deep sedimentary basin in northern Italy, is prone to heavy shaking during earthquakes. Seismic hazard assessment must account for local variation in wave amplification. Standard ground motion prediction equations may fail to picture the complexity of strong lateral gradients in seismic response, due to sharp structural heterogeneity. For this reason, there is an increasing demand for full waveform predictions for engineering applications. Here, we present an implementation of a hybrid broadband simulation based on the method of Mai et al. (Bull Seismol Soc Am 100(6):3338–3339, 2010), to obtain complete broadband seismograms of 0.1–10 Hz. With this method, low frequency (< 1 Hz) and high frequency (1–10 Hz) seismograms are simulated separately using a deterministic and a stochastic method, respectively. We apply the method to four events recorded within the Po basin, with magnitude ranging from Mw = 4.4 to Mw = 5.6. The low frequency (LF) simulation is performed using SPECFEM3D on a few test subsurface velocity models. The three-dimensional velocity model MAMBo (Molinari et al. in Bull Seismol Soc Am 105(2A):753–764, 2015)—consisting of a detailed structural description of the basin, based on extensive active-source data, embedded within a regional 3D crustal model—provided the best results for broadband simulations that most closely corresponded with the observations. It performed better than an ambient noise tomography model with more accurate S-wave velocities but less well defined layer topographies, emphasizing the importance of first order velocity discontinuities. The high frequency (HF) seismograms are simulated using the multiple scattering approach of Zeng et al. (J Geophys Res Solid Earth 96(B1):607–619, 1991). The scattering coefficients are obtained by performing a non linear inversion for each station to find best fitting synthetic envelopes. HF energy is then combined at \(\sim\) 1 Hz to match the amplitude and phase spectra of the LF signal. We are able to simulate full waveforms throughout the Po Plain, of which shaking duration matches observed data for stations located in the basin. Shaking amplitudes are generally overestimated in the low frequency simulation by the MAMBo velocity model. Updating the MAMBo velocity model with more accurate S-wave velocity information of the ambient noise tomography model should improve the fit in future simulations.

Tooth Root Crack Detection of Planet and Sun Gears Based on Resonance Demodulation and Vibration Separation

Due to the epicyclic motion of planet gears, the vibration picked up from planetary gearboxes is different from that observed from the fixed-axis gearboxes. In particular, the vibration transfer path is time-varying, which makes the time synchronous averaging (TSA) not directly usable to reduce the nonsynchronous interferences for improving the signal-noise ratio (SNR) of vibration. Hence, it is difficult to detect teeth faults of planet and sun gears. In order to address this issue, a novel scheme is proposed in this paper, which combines the vibration separation, equi-angle resampling, and resonance demodulation approaches. In the proposed scheme, the complex envelope of the vibration is extracted by the fast kurtogram algorithm at first. Then, the envelope is equi-angle resampled to eliminate the inevitable speed fluctuations. Subsequently, a window function is used to grab the envelope data series at a fixed angular position related to the ring gear, such that the problems caused by time-varying vibration transfer paths are solved. Then, synthetic envelopes can be constructed by connecting the data in the data blocks according to the teeth mesh sequences of the interesting gear, where a data mapping scheme and a synthetic envelope determining strategy based on maximum kurtosis are introduced. Furthermore, the TSA is applied to the synthetic gear envelope to improve the SNR. Finally, spectral analysis is utilized to expose the characteristic frequencies. The effectiveness of the proposed method is validated by comparative experiments with the normal and faulty planet and sun gears in a planetary gearbox test rig.

A New Drainpipe‐Envelope Concept for Subsurface Drainage Systems in Irrigated Agriculture

AbstractOn irrigated lands, drainpipe performance is often below standard due to clogging, siltation and root growth inside the pipe. To tackle these problems, an innovative pipe–envelope concept was tested on a 50 ha pilot area in Harran, Turkey, in 2015 and 2016. The new concept, HYDROLUIS, consists of a corrugated inner pipe with three rows of perforations at the top and an unperforated outer pipe that covers about 2/3 of the inner pipe leaving only the unperforated bottom part of the inner pipe in contact with the soil. The main advantages of the new concept are that it works for a wide range of soil textures and there is better protection against root growth inside the pipe. The new concept was compared with a geotextile envelope, a gravel envelope and a control with no envelope. The HYDROLUIS and gravel envelopes had a significantly lower entrance resistance compared to the geotextile, the best drain performance and no signs of sedimentation nor of root growth inside the pipe. The production costs of the HYDROLUIS envelope are comparable to those of pre‐wrapped synthetic envelopes and considerably lower than gravel envelopes. It can be concluded that the HYDROLUIS envelope is a promising alternative for sand/gravel or synthetic envelopes in irrigated lands. © 2018 The Authors. Irrigation and Drainage published by John Wiley &amp; Sons Ltd on behalf of International Commission for Irrigation and Drainage

Differential Monte Carlo method for computing seismogram envelopes and their partial derivatives

AbstractWe present an efficient method that is applicable to waveform inversions of seismogram envelopes for structural parameters describing scattering properties in the Earth. We developed a differential Monte Carlo method that can simultaneously compute synthetic envelopes and their partial derivatives with respect to structural parameters, which greatly reduces the required CPU time. Our method has no theoretical limitations to apply to the problems with anisotropic scattering in a heterogeneous background medium. The effects of S wave polarity directions and phase differences between SH and SV components are taken into account. Several numerical examples are presented to show that the intrinsic and scattering attenuation at the depth range of the asthenosphere have different impacts on the observed seismogram envelopes, thus suggesting that our method can potentially be applied to inversions for scattering properties in the deep Earth.

Investigating the Performance of Gravel and Synthetic Envelopes in Subsurface Drainage

In this research, the hydraulic behavior of two kinds of envelopes including synthetic envelope, PP450 and gravel envelope with USBR standard in two soil tank models with silty loam texture was investigated. Three water heads including 55, 75 and 105 cm (water logging) from drain level were used. The discharge of pipe drain in the steady state condition for gravel envelope and at 55, 75 and 105 cm water heads was 188.9, 172.0 and 897.0% more than those in PP450, respectively. Envelope hydraulic conductivity rates at gravel envelope for 55, 75 and 105 cm water heads were 24.6, 14.0 and 21.2 times higher than those in PP450, respectively, and gradient ratios in these water heads for gravel envelope were 14.5%, 2.8% and 14.2% lower than those for synthetic envelope. There were also different behaviors in the two kinds of envelopes for hydraulic conductivity and entrance resistance of pipe and envelope in 55 and 75 cm water heads relative to 105 cm. In general, according to the measured parameters in this research, gravel envelope showed a better performance.

Intrinsic and scattering attenuation as derived from fluid induced microseismicity at the German Continental Deep Drilling site

Hydraulically induced microseismicity is used to study high-frequency attenuation properties (6–72 Hz) in an enhanced geothermal system. Intrinsic and scattering attenuation are separated by jointly inverting seismogram envelopes for structural parameters, source and site effects. Modelling of synthetic envelopes is based on radiative transfer theory. To speed up inversion, an analytical solution of the radiative transfer equation for a 3-D isotropic scattering medium is implemented. In order to compensate for the actual anisotropic scattering, a smoothing algorithm is applied to introduce envelope broadening and peak delay. The approach is tested with seismic data from four fluid-induced earthquakes (Mw ≤ 1) recorded by a temporary seismic network at the German Continental Deep Drilling (KTB) site at epicentral distances of less than 20 km. Full S-wave envelopes are inverted in 12 overlapping frequency bands with centre frequencies between 1.5 and 72 Hz. With data sampling at 200 Hz and high-frequency S-wave sources, attenuation estimates are obtained for the rarely probed frequency range between 30 and 70 Hz. From the inversion, we infer average values of the transport scattering coefficient g*, and the intrinsic absorption parameter b, as well as corresponding quality factors Qs and Qi. By comparison with attenuation estimates from regions with different tectonic activities, we see that both Qs and Qi for the investigated geothermal region fit best to moderate scattering and intrinsic regimes as obtained in tectonically active regions. A comparison with a regional attenuation model for southern Germany proves that attenuation estimates are scale-dependent. To compare intrinsic and scattering attenuation in the KTB region the transport mean free path (TMFP) and the absorption length (la) are calculated. For both, we find a clear frequency dependence proportional to f −0.8 (TMFP) and f −0.3 (la). TMFP decreases from 340 km at 6 Hz to 60 km at 72 Hz, whereas absorption length drops from 40 to 20 km, respectively. Thus, intrinsic absorption dominates over scattering attenuation by at least one order of magnitude. The influence of scattering becomes more significant towards higher frequencies. Moreover, comparing the apparent attenuation (inverse sum of TMFP and la) to values estimated with the spectral ratio technique, achieves a good agreement with mean deviations in the order of 3–5 per cent. From the frequency dependence of TMFP, it can be inferred that a von Karman-type of random medium with a Hurst exponent of κ = 0.11 is a good model for representing the stimulated reservoir at the KTB. The fractal distribution of scatterers agrees well with results derived from independent analysis of acoustic logs.

Performance of Geo-synthetic Filter Materials as Drain Envelope in Land Reclamation in Haryana

Geo-synthetic envelope materials are increasingly replacing gravel/sand in subsurface drainage systems commonly installed to reclaim waterlogged salt affected lands. The availability constraints of gravel/sand envelopes, transport cost, design complexities, application difficulties in mechanized construction helped the switchover to synthetic envelopes, especially geo-synthetic materials. Geo-synthetic envelope materials used in Haryana Operational Research Project (HOPP) were found to be strong enough to withstand handling during transport, manual or machine wrapping, and for use with a drainage pipe laying machine. These materials were tested in the laboratory to characterize them and recommend their use as envelope materials. The field data after 3 and 6 years of installation of the drainage system at Jhajjar in Haryana with geo-synthetic envelope materials revealed much less silting of pipes than the recommended guidelines. The characteristics of a woven synthetic material used to wrap perforated collector pipes are discussed. A machine earlier designed to wrap the geo-synthetic material was evaluated for its capacity. The machine could handle 1.5-2.0 km of pipe daily with 8 semi-skilled labourers, enabling to cope up with the demand of a pipe-laying trencher machine that could lay about 1.5 km of laterals in a single day.

Evidence for P′P′ asymmetrical scattering at near podal distances

We report strong short period (0.5–1.2 Hz) precursors to P′P′df at podal to short distances (0–50°) with advance time around 60s. From FK analysis, we find that the precursors at epicentral distance of ∼35° arrive along back‐azimuth about +/−120° off the great circle paths (asymmetrical path) with slowness between 2–4 sec/deg, arguing against propagation path in the inner core. Polarization analysis also supports wave propagation in the outer core. Timing and shape of the precursors' waveform envelopes are well matched with synthetic envelopes taking into account the scattering from the rough free surface and volumetric heterogeneities inside the Earth along asymmetrical propagation path. Therefore the precursors are very probably generated with asymmetrical scattering mechanism. This interpretation does not require extra discontinuities or a layer of strong small scale heterogeneities in the upper mantle, which are inferred from P′P′ precursors when only symmetrical scattering is assumed.

Comparison of Fuzzy Inference System and Multiple Regression to Predict Synthetic Envelopes Clogging

Geo-synthetic materials are being used with acceptable performance in soil and water projects worldwide. Geotextiles are one of the categories of geo-synthetics being used in drainage systems. First generation of geotextiles used in the late 1950’s as an alternative for gravel envelopes. In this research two methods (multiple regression and fuzzy interference system) evaluate to predict synthetic envelope clogging. In multiple regression method the correlation coefficients for PP450, PP700 and PP900 are 62.66%, 79.37% and 90.62%, respectively and results of fuzzy interference system and decision tree showed that this method have high potential in comparison with multiple regression and values of total classification accuracy for PP450, PP700 and PP900 are 98.6%, 97.3% and 98% respectively. Then final results of this research showed fuzzy interference systems by using decision tree have high potential to predict clogging in envelops.

Two-layer earth model corrections to the MLTWA estimates of intrinsic- and scattering-attenuation obtained in a uniform half-space

SUMMARY Following the numerical scheme of Yoshimoto we synthesized seismogram envelopes in the multiple scattering framework. We supposed the earth model constituted by a inhomogeneous crust overlying a transparent mantle. In this model velocity is assumed depth-dependent through a continuous function of the depth, v = v(h); Moho discontinuity is approximated by a sharp increase of the velocity around the crust–mantle boundary; inhomogeneity in the crust is parametrized through a depth-dependent scattering coefficient (the inverse of mean free path) g = g0 f (h), with f (h) function of depth, and g0 the scattering coefficient at zero depth; intrinsic attenuation is parametrized in terms of the intrinsic attenuation coefficient, ηi , that is assumed independent of depth. Generating a suite of energy envelopes as a function of lapse time and distance, for reasonable values of B0 , the seismic albedo and Le −1 , the extinction length inverse (which are functions of g0 and ηi ), we span a wide range including most of the measurements done through the world. Then, we apply the ordinary MLTWA technique to these synthetic envelopes. In this application, we assume a constant g and a constant velocity, v = which equals the average of v(h) calculated in the depth range characteristic of the volume encompassed by the scattered waves. In this way, we obtain the estimates of B0, and Le −1 , for a constant half-space. The relationship between the estimates of B0 and Le −1 , obtained assuming half-space, and the correspondent values used in the simulation, results to be well approximated by a second-order polynomial. Then, evaluating the best fit polynomial coefficients, we obtain a correspondence map between attenuation parameters retrieved for a uniform model with those characteristic of a more realistic structure. This map is useful to reinterpret all the couples B0 and Le −1 already calculated through the world in geological structures similar to the one adopted in our simulation. Results show that scattering and intrinsic-attenuation coefficients estimated using MLTWA in the assumption of a uniform half-space are always overestimated.

PERFORMANCE EVALUATION OF SYNTHETIC ENVELOPES IN INDIRA GANDHI COMMAND AREA, RAJASTHAN

ABSTRACT The present study was undertaken to evaluate the performance of synthetic envelopes for sub-surface drainage under the field conditions at Lunkarnsar Farm, Indira Gandhi Canal Command Area, Bikaner and laboratory conditions at College of Technology and Engineering, Udaipur. Three types of synthetic envelopes viz. HG 22, SAPP 240 and CAN 2 were evaluated by using sand tank model and permeability apparatus to compare their performances in terms of entrance resistance and hydraulic conductivities of soil envelope system. The experiments revealed that the values of entrance resistance for envelope HG 22, SAPP 240 and CAN 2 were 1.95 day/m, 1.33 day/m and 1.51 day/m, respectively of Lunkarnsar soil. The hydraulic conductivities for envelope HG 22, SAPP 240 and CAN 2 of the total thickness (k-total) were found to be 4.53 cm/hr, 5.22 cm/hr and 4.91 cm/hr and of the contact layer (k-contact) were found to be 3.009 cm/hr, 3.62 cm/hr and 3.27 cm/hr, respectively. The hydraulic conductivity of contact layer was found lower than that of the total layer which confirmed the soil envelope interface. The Hydraulic conductivity for SAPP 240 filter was found to be the highest and entrance resistance was found to be lowest. The SAPP 240 filter is recommended for Indira Gandhi Command Area for subsurface drainage system.

Design and performance of materials for subsurface drainage systems in agriculture

During the second half of the 20th century, numerous land drainage systems using new materials for the drain channels that often function inadequately due to biochemical and mechanical clogging, were developed. The design of drainpipes and envelope materials used for these land drainage systems was based on both theoretical and experimental investigations. This contribution reviews the simultaneous development of theory and practical experience in Europe and North America. The results of the effect of perforation shape and pattern in drainpipes and of envelope materials on drainage performance are summarized and the latest design criteria of granular materials and synthetic envelopes presented. Theoretical investigations are associated with field data on the performance of drainage materials. A thorough knowledge, not only of the flow conditions, but also of the physical soil properties in the vicinity of the drains is imperative for a correct interpretation of field data. This contribution represents the main features on drainpipes and envelope materials, and the physical soil processes that occur in the vicinity of the drain. It gives an overview of the research work done referring to numerous publications where relevant and detailed information can be found.

Separation of depth-dependent intrinsic and scattering seismic attenuation in the northeastern sector of the Italian Peninsula

SUMMARY We investigated the intrinsic dissipation and scattering properties of the lithosphere under the Friuli region (northeastern Italy) using two hypotheses: (i) a uniform earth model and (ii) two ‘reasonable’ non-uniform, layered crustal models. For case (i) we measured the coda Q, and used the multiple-lapse time window analysis (MLTWA) technique to obtain separate estimates of intrinsic absorption and scattering attenuation. Results for the uniform earth model show that the lithosphere in northeastern Italy is characterized by a low-scattering attenuation (small scattering Q-inverse, Q −1 ), and by a relatively high intrinsic attenuation (high intrinsic Q-inverse, Q −1 ). A comparison between the investigated region and other areas around the world shows that both Q −1 and Q −1 for the Friuli region are among the lowest values ever measured, with the exception of the southern Apennines, which has the lowest measured Q −1 . For case (ii), numerical simulation of the energy envelopes was performed using two-layered earth models, where the values of the intrinsic and scattering attenuation coefficients are both within ‘reasonable ranges’ when compared with the geological information. The theoretical envelopes calculated for the homogeneous model give a good fit to the synthetic envelopes calculated for the layered models; the best fit is obtained for scattering attenuation coefficients of the uniform model always greater than those of the layered model. The main result is consequently that scattering Q −1 obtained using the MLTWA under the assumption of a uniform medium is overestimated, on average, by a factor 2. Finally, coda Q −1 appears to be closer to the total Q −1 than to the intrinsic Q −1 ,a spredicted