High Shear Wave Velocity Research Articles

Seismicity and structure of Nazca Plate subduction zone in southern Peru

We define subducting plate geometries in the Nazca subduction zone by (re)locating intra-slab earthquakes in southern Peru (14–18°S) and using previously published converted phase analysis results to clarify the slab geometry and inferred relationships to the seismicity. We also provide both P- and S-wave velocity models of the subducting Nazca Plate and mantle layer above the slab using double-difference tomography to understand upper-plate volcanism and subduction zone process. The double-difference constraints for determining the hypocenters and velocity model ensure high accuracy of the relative location of earthquakes with respect to velocity structure. The relocated seismicity shows a smooth contortion in the slab-dip transition zone for ∼400 km between the shallow (30°)-to-flat dipping interface to the northwest and the 30°-dipping interface to the southeast. We find a significant slab-dip difference (up to 10°) between our results and previous slab models along the profile region sampling the horizontal slab at a depth of ∼85–95 km. Robust features in both P- and S-wave tomography inversions are both arc-normal and along-arc velocity variations. In the arc-normal direction, all profile results show that the slab velocities beneath the forearc (down to a depth of ∼100 km) transition to higher velocities beneath the backarc (at ∼100–140 km depth). In the along-arc direction, velocities of the subducting flat slab are shown to be depressed compared to those of the normal-dip slab. In addition, high shear-wave velocities and low Vp/Vs are detected in the mantle layer above the flat slab, indicating its cold and dry environment. Such differences in the velocity structures for the slab and mantle wedge between the two regions may indicate different hydration states, which greatly affects the upper-plate structure of southern Peru.

Carotid Plaque Stiffness Measured with Supersonic Shear Imaging and Its Correlation with Serum Homocysteine Level in Ischemic Stroke Patients.

ObjectiveTo ascertain the feasibility of using shear wave velocity (SWV) in assessing the stiffness of carotid plaque by supersonic shear imaging (SSI) and explore preliminary clinical value for such evaluation.Materials and MethodsSupersonic shear imaging was performed in 142 patients with ischemic stroke, including 76 males and 66 females with mean age of 66 years (range, 45–80 years). The maximum, minimum, and mean values of SWV were measured for 129 carotid plaques. SWVs were compared between echolucent and echogenic plaques. Correlations between SWVs and serum homocysteine levels were investigated. Based on neurological symptom, the surrogate marker of vulnerable plaque (VP), binary logistic regression was performed and area under curve (AUC) of homocysteine only and homocysteine combing SWVmean was calculated respectively.ResultsEchogenic plaques (n = 51) had higher SWVs than echolucent ones (n = 78) (SWVmin 3.91 [3.24–4.17] m/s vs. 1.51 [1.04–1.94] m/s; SWVmean, 4.29 [3.98–4.57] m/s vs. 2.09 [1.69–2.41] m/s; SWVmax, 4.67 [4.33–4.86] m/s vs. 2.62 [2.32–3.31] m/s all p values < 0.01). Pearson correlation analysis showed that stiffness of plaques was negatively correlated with homocysteine level. R values for SWVmin, SWVmean, and SWVmax were −0.205, −0.213, and −0.199, respectively. Binary logistic regression analysis showed that sex (p = 0.008), low-density lipoprotein (p = 0.015), triglycerides (p = 0.011), SWVmean (p = 0.004), and hyper-homocysteinemia (p = 0.010) were significantly associated with symptomatic ischemic stroke. Receiver operating characteristic curves revealed that SWVmean combing serum homocysteine level (AUC = 0.67) presented better diagnostic value than serum homocysteine only (AUC = 0.60) for symptomatic ischemic stroke.ConclusionSupersonic shear imaging could be used to quantitatively evaluate stiffness of both echolucent and echogenic carotid plaques. More importantly, SWVs of plaques were not only correlated to serum homocysteine level, but also associated with symptomatic ischemic stroke, suggesting that SSI might be useful for understanding more about VP.

Examining the Discrepancy between Forecast and Observed Liquefaction from the 2015 Gorkha, Nepal, Earthquakes

Many ground failures resulted from the 2015 Nepal earthquake sequence, including landslides, rockfalls, liquefactions, and cyclic failures. And whereas the amount and extent of landsliding were relatively consistent with predictions for a Mw7.8 main shock, the amount and extent of liquefaction were not. We present a summary of liquefaction field observations that we made as part of the Geotechnical Extreme Events Reconnaissance (GEER) investigations. The liquefaction that did occur in the Kathmandu Valley was limited in its spatial extent, and the postliquefaction deformations were small. Prior earthquakes in this region have been reported to have caused greater liquefaction-related failures, and liquefaction hazard–mapping studies predicted widespread liquefaction hazard from an event of this size. We explore two possible reasons at the regional scale for the limited liquefaction from this earthquake sequence: drawdown of the groundwater table and high near-surface shear wave velocity. Our study finds that pumping has depressed the groundwater table across the Kathmandu Valley by 13–40 m since 1980, thereby decreasing the amount of near-surface liquefiable material and increasing the nonliquefiable “crust” layer. The regional slope-based VS30for the valley is on average higher than that for liquefaction sites in a global database of observed liquefaction. A global geospatial model for liquefaction occurrence shows low liquefaction potential in the Kathmandu Valley consistent with the observed patterns.

Compaction and mechanical strength of Middle Miocene mudstones in the Norwegian North Sea – The major seal for the Skade CO2 storage reservoir

This study has investigated petrophysical, acoustic and geomechanical properties of Middle Miocene mudstones in the Norwegian North Sea as the primary caprock for Skade CO2 storage reservoir. To evaluate the seal properties, we analyzed collected drill cuttings and measured well logs from well 16/4-1, in addition to an extensive well log database in the Northern North Sea. The studied caprock was identified as siliceous ooze-rich mudstones with low bulk density, high shear wave velocity, and low Vp/Vs ratio. The abundance of siliceous skeletal material resulted in a significant shift from the overall trend of mudstones within the Hordaland Group. The estimated scenarios for S-wave velocity depicted that the ooze-rich mudstones have the highest brittleness of the Hordaland Group semi-consolidated rocks. The brittleness indices in well 16/4-1 illustrated that the mineralogical composition-based indices significantly overestimate brittleness compared to the elastic-based indices. While the caprock for Skade CO2 storage reservoir showed an overall ductility, the bottom 30m demonstrated an increased brittleness profile. The more brittle ooze-rich mudstones also indicated the lowest estimation of fracture pressure compared to other scenarios. The research outcomes emphasize on the influence of mudstone type and microstructure on the macroscale physical properties of shallow semi-compacted CO2 caprocks.

The 2016 Kumamoto Mw = 7.0 Earthquake: A Significant Event in a Fault–Volcano System

AbstractThe 2016 Kumamoto earthquake sequence occurred on the Futagawa–Hinagu fault zone near the Aso volcano on Kyushu island. The sequence was initiated with two major (Mw ≥ 6.0) foreshocks, and the mainshock (Mw = 7.0) occurred 25 h after the second major foreshock. We combine GPS, strong motion, synthetic aperture radar images, and surface offset data in a joint inversion to resolve the kinematic rupture process of the mainshock and coseismic displacement of the foreshocks. The joint inversion results reveal a unilateral rupture process for the mainshock involving sequential rupture of four major asperities. The slip area of the foreshocks and mainshock and the aftershock loci form a detailed complementary pattern. The mainshock rupture terminates near the rim of the caldera, leaving a ~10 km long gap of aftershocks. This area is characterized by high temperature and low shear wave velocity, density, and resistivity, which may be related to the partially melted geothermal condition. Ductile material property near the volcano may act as a “material barrier” to the dynamic rupture. Topographic weight of the caldera increases compressional normal stress on the fault plane, which may behave as a “stress barrier.” Long‐term seismic hazard and deformation behaviors related to these two types of barriers are discussed in terms of the associated frictional mechanism. Significant postseismic creeps observed near the volcano area indicates a velocity strengthening frictional behavior near the rupture termination, which confirms that the “material barrier” mechanism is likely the dominant rupture termination mechanism.

Achilles and patellar tendinopathy display opposite changes in elastic properties: A shear wave elastography study.

To compare tendon elastic and structural properties of healthy individuals with those with Achilles or patellar tendinopathy. Sixty-seven participants (22 Achilles tendinopathy, 17 patellar tendinopathy, and 28 healthy controls) were recruited between March 2015 and March 2016. Shear wave velocity (SWV), an index of tissue elastic modulus, and tendon thickness were measured bilaterally at mid-tendon and insertional regions of Achilles and patellar tendons by an examiner blinded to group. Analysis of covariance, adjusted for age, body mass index, and sex was used to compare differences in tendon thickness and SWV between the two tendinopathy groups (relative to controls) and regions. Tendon thickness was included as a covariate for analysis of SWV. Compared to controls, participants with Achilles tendinopathy had lower SWV at the distal insertion (Mean difference MD; 95% CI: -1.56; -2.49 to -0.62m/s; P<.001) and greater thickness at the mid-tendon (MD 0.19; 0.05-0.33cm; P=.007). Compared to controls, participants with patellar tendinopathy had higher SWV at both regions (MD 1.25; 0.40-2.10m/s; P=.005) and greater thickness proximally (MD 0.17; 0.06-0.29cm; P=.003). Compared to controls, participants with Achilles and patellar tendinopathy displayed lower Achilles tendon elastic modulus and higher patellar tendon elastic modulus, respectively. More research is needed to explore whether maturation, aging, or chronic load underlie these findings and whether current management programs for Achilles and patellar tendinopathy need to be tailored to the tendon.

Study of crustal structure and geological implications of southwestern margin of Northeast India

It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average VP/VS ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38–45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of VP/VS ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson’s ratio (1.69–1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of VP/VS ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins.

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

AbstractThe northeastern margin of Tibet is of key importance in understanding the uplift and expansion of Tibetan Plateau. In this research, we perform Rayleigh wave tomography from 20 s to 167 s using the data recorded by China Digital Seismic Network and several portable seismic arrays in Northeastern Tibet and adjacent areas. Our resultant 3‐D shear wave velocity model exhibits strong lateral variations in the lithosphere. High shear wave velocities are observed in the mantle of the cratonic Ordos and Yangtze Blocks, as well as the East Qinling Orogen. The Qilian Orogen is underlain by a ∼120 km thick lithosphere of intermediate velocities and a low‐velocity layer of asthenospheric mantle below the depth of 120 km. Low velocities are characteristic in the middle‐to‐lower crust of the Songpan‐Ganzi Terrane and the West Qinling Orogen, possibly representing the crustal flow penetrating the Kunlun Fault. An uppermost mantle low‐velocity zone is found in the same location, indicating either the asthenosphere upwelling or the transitional crust‐mantle boundary layer. Our observations have two tectonic implications. First, the large‐scale eastward Tibetan material extrusion into Eastern China through the East Qinling Orogen is unlikely to be an ongoing process above 200 km depth; second, the southward subduction of the North China Craton toward Northeastern Tibet may not have fully developed in this region. Furthermore, we propose that the difference in the lithospheric strength between the Qaidam Block and the West Qinling Orogen is a critical element to control the tectonics in the northeastern margin of Tibet.

Pancreatic Elastography From Acoustic Radiation Force Impulse Imaging for Evaluation of Diabetic Microangiopathy.

The purposes of this study were to compare pancreatic shear-wave velocity (SWV) in subjects with and those without diabetic microvascular complications and to investigate the feasibility of pancreatic SWV in evaluating diabetic microangiopathy. SWV measurements were prospectively performed in 115 patients with diabetes mellitus and 115 healthy persons by use of acoustic radiation force impulse imaging. Patients with diabetes were divided into subgroups with and without microangiopathy. Pancreatic SWV was compared in three groups. Factors associated with increased SWV were studied. Pancreatic SWV increased significantly in the subgroups with diabetes mellitus compared with the control group (p < 0.01). Especially, the SWV in the pancreatic body was significantly higher when microangiopathy was present (p < 0.01). In patients with diabetes, microangiopathy (standardized β = 0.208, p = 0.022), age (standardized β = 0.265, p = 0.004), and total cholesterol level (standardized β = 0.223, p = 0.011) were positively and markedly correlated with high SWV in the pancreatic body. The increased SWV in the pancreatic body was significantly related to the presence of microangiopathy. It is feasible to use SWV in the pancreatic body to evaluate diabetic microangiopathy.

Conventional US combined with acoustic radiation force impulse (ARFI) elastography forprediction of triple-negative breast cancer and the risk of lymphatic metastasis.

To evaluate the combination of conventional ultrasound (US) and acoustic radiation force impulse (ARFI) elastography in predicting triple-negative breast cancer and the likelihood of lymphatic metastasis. A total of 178 women presenting from May 2013 to September 2015 with pathologically proven triple-negative (n = 60) or hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative breast cancer (n = 118) were reviewed. Conventional US and ARFI imaging including Virtual touch tissue image (VTI) and Virtual Touch tissue Quantification (VTQ), were performed for each breast nodule. Parameters collected included patient age, lymph node involvement, histological grade, tumor subtype, appearance on conventional US, shear wave velocity (SWV) value, VTI score and the boundary on VTI. The ARFI findings were compared with the pathological findings. Younger age (P < 0.001), higher histological grade (P < 0.001), lymphatic metastasis (P < 0.001), more nodes involved (P = 0.001), larger tumor size (P = 0.008), regular shape (P = 0.032), high VTI score (P = 0.006), unclear VTI boundary (P = 0.033), SWV ≥3.51 m/s (P = 0.015) were significantly associated with triple-negative breast cancer. High VTI score (P = 0.004) and a high SWV ≥4.15 m/s (P = 0.002) were significantly associated with lymphatic metastasis. Conventional US combined with ARFI may be used to predict triple-negative breast cancer. Those cancers with higher SWV and the high VTI score have a higher likelihood of lymphatic metastasis.

Evaluation of Post-Stroke Spastic Muscle Stiffness Using Shear Wave Ultrasound Elastography

Current clinical evaluations of post-stroke upper limb spasticity are subjective and qualitative. We proposed a quantitative measurement of post-stroke spastic muscle stiffness by using shear-wave ultrasound elastography and tested its reliability. Acoustic radiation force impulse with shear wave velocity (SWV) detection was used to evaluate stiffness of the biceps brachii muscles at 90° and 0° elbow flexion. In 21 control subjects, SWV did not significantly differ between dominant and non-dominant sides at either flexion angle (0°: p = 0.311, 90°: p = 0.436). In 31 patients who had recent stroke, SWV was significantly greater on the paretic side than on the non-paretic side at both 90° (2.23 ± 0.15 m/s vs. 1.88 ± 0.08 m/s, p = 0.036) and 0° (3.28 ± 0.11 m/s vs. 2.93 ± 0.06 m/s, p = 0.002). The physical appearance of arms and forearms of our patients and controls prevented blinding of the rater to paretic or non-paretic side. At 90°, SWV on the paretic side correlated positively with modified Ashworth scale and modified Tardieu scale (spasticity severity) and negatively with Stroke Rehabilitation Assessment of Movement score (motor function impairment). The intra-class correlation coefficients of intra-rater and inter-rater reliability for SWV measurements were classified as excellent. In conclusion, high SWV was associated with high spasticity and poor function of the post-stroke upper limb, suggesting possible use as a reliable quantitative measure for disease progression and treatment follow-up.

Shear wave elastography of the testes inahealthy study collective - Differences instandard values between ARFI andVTIQtechniques.

Shear wave elastography (SWE) is a recent technique in the assessment of tissue elasticity. Different elastography techniques have been described over the years.Acoustic Radiation Force Impulse Imaging (ARFI) uses mechanical excitation of tissue to create detectable shear waves, a higher shear wave velocity being associated with an increased tissue stiffness.The Virtual Touch Tissue Imaging Quantification (VTIQ) method uses a mechanical push pulse as well, additionally creating a colour-coded map, in which tissue stiffness can be measured within a stored map on the ultrasound device after measurement.ARFI has been used in determining standard values in testes of a healthy study collective, VTIQ has already been used in the evaluation of unclear scrotal masses.Both techniques allow an operator-independent examination without application of mechanical pressure. The aim of this study was to determine whether there is a statistically significant difference between shear wave velocity values of both techniques in a healthy collective. Twenty patients without known testicular pathology underwent standard B-mode sonography and additional shear wave elastography in the ARFI mode as well as the VTIQ technique of both testes using the Siemens Acuson S2000™ and S3000™ ultrasound devices (Siemens HealthCare, Erlangen, Germany).Measurements of shear wave velocity were performed in the upper pole, the central portion and the lower pole separately for each testis. Values were described in m/s.Statistical evaluation was performed using paired t-test analysis. We measured a mean shear wave velocity of 0.81 m/s using ARFI and 1.07 m/s with VTIQ.Shear wave velocities determined by VTIQ were all significantly higher than values gained in the ARFI mode. (p < 0.001 to p = 0.007). Values were between 0.22 and 0.29 m/s higher, when the examination was performed using VTIQ. ARFI and VTIQ elastography modes both proved to be feasible techniques in the assessment of testicular tissue elasticity. Consideration of higher values for VTIQ is important, when different elastography measurement results are compared, especially for the application of devices in a clinical setting, e.g. in the work-up of scrotal masses.A calculable factor for a comparison between both devices is desirable, but to be further assessed in largerstudies.

Breast Cancer Imaging by Color Doppler Shear Wave Elastography

In shear wave elastography, complicated shear wave wave-front caused by the reflection, refraction, and diffraction at the tissue boundary degrades the accuracy of velocity measurement. If the shear wave wave-front is visualized in real-time, the accuracy increases because the velocity is estimated along the shear wave propagation direction. Moreover, observed wave-front pattern provides valuable information about tissue structure, which makes the detection of the stiff part easier. We have proposed a novel shear wave elastography (Color Doppler Shear Wave Imaging: CD SWI) [Y.Yamakoshi, et al. IEEE tans on UFFC. 64, 340 (2017)]. Continuous shear wave of a frequency that is n/4 (n being an odd number) times the PRF is introduced from the tissue surface. Then, the shear wave wave-front appears simultaneously as a stripe pattern on conventional ultrasound color Doppler image. This cost-effective shear wave elastography is implemented on ACUSON S3000 (Siemens). The shear wave frequency is 235.3Hz. Shear wave velocity measured by CD SWI was compared with that by ARFI for breast phantom. Shear wave velocities by two methods showed good correlation, but the standard deviation of CD SWI was 42% of that of ARFI. Malignant lesions were imaged by CD SWI as an area with high shear wave velocity. Inherent shear wave propagation around a malignant lesion was also observed. It is suggested that a combination of shear wave image of CD SWI and B-mode image improves the sensitivity in detection of malignant lesions in breast tissue.

Anatomy of the Colima volcano magmatic system, Mexico

Colima volcano is one of the most active volcanoes in continental north America. It is located within the Colima graben on the western part of the Colima rift zone. Although extensively studied, the internal structure and deep magmatic system remains unknown. This research gives new clues to understand how and where magmas are produced and stored at depth. Using ambient seismic noise, we jointly invert for Rayleigh and Love wave dispersion curves for both phase and group velocity, which is applied for the first time in a volcanic environment. We invert for both the shear wave velocity and radial anisotropy. The 3D high resolution shear wave velocity model shows a deep, large and well-delineated elliptic-shape magmatic reservoir below the Colima volcano complex at a depth of about 15 km. On the other hand, the radial anisotropy model shows a significant negative feature (i.e., VSV>VSH) revealed from ≥35 km depth until the top of the magma reservoir at about 12 km depth. The latter suggests the presence of numerous vertical fractures where fluids, rooting from a well-known mantle window, can easily migrate upward and then accumulate in the magma reservoir. Furthermore, the convergence of both a low velocity zone and a negative anisotropy suggests that the magma is mainly stored in conduits or inter-fingered dykes as opposed to horizontally stratified magma reservoir.

Investigation of site properties in Adapazarı, Turkey, using microtremors and surface waves

Determination of suitable areas for new residential buildings is crucial to increase the resilience of buildings against earthquake hazards. After the 1999 Izmit earthquake Mw 7.4, the city of Sakarya has been expanding rapidly in terms of both the population and number of superstructures. Despite the fact that Sakarya suffered several large earthquakes in the last two decades, the geophysical properties of the region have not been adequately investigated. In this study, the site properties of Sakarya University, Esentepe Campus, and its surrounding Serdivan district, which is one of the important parts of the city, are determined using microtremor measurements and surface wave analysis. Nakamura’s spectral ratio method (spectral ratio between the horizontal and vertical components, H/V or HVSR) was used to determine the fundamental frequency and site amplification values. The shear wave velocity profiles of the studied sites were determined using the multichannel analysis of surface waves method. Seismic measurements were performed at 34 locations to record the surface waves in the area. The fundamental frequency and site amplification values are determined as 1.02–11.68 and 1.33–5.96 Hz, respectively, from the microtremor measurements. The fundamental frequency is between 4.0 and 11.5 Hz in the campus area and between 1.3 and 2.0 Hz near the D-100 intercity highway. The site amplification was determined to be 1–2.5 in the campus area. The greatest site amplification (6) is obtained at thick alluvium deposits in the valley between hills. The average shear wave velocity values are within the range of 300 and 1120 m/s. Some parts located on the hill area have better soil condition (B) categories, according to the National Earthquake Hazard Reduction Program, and have comparatively high shear wave velocities in the range of 740–1080 m/s, whereas low velocity values are found at the thick alluvium deposits (D). We found that the geological properties and topographies play very important roles on the shear wave velocity and the amplification factors in the investigated area.

Soil and Subsurface Sediment Microzonation Using with Seismic Refraction Tomography for Site Assessment (Case Study: IKIA Airport, Iran)

The site effects relating to the amplification of ground motion under earthquake loading are strongly influenced by both the subsurface soil condition and the geologic structure. In this study, for site characterization at the Imam Khomeini International Airport (IKIA) area in south of Tehran, in-situ seismic refraction tomography were carried out as a part of site investigations project, in addition geologic setting, borehole drilling, ground waters information and measurements. Based on seismic refraction studies, three layers are separable which with increasing in depth the S and P wave velocity is increased and this indicates increasing in compaction of soil and geologic materials. In the second and third separated layers, the zones with low and high seismic shear wave velocity is approximately equal, and northeast and southwest of the airport site has the low velocities, in addition to containing loose soils, highly weathered stones, and low depth to groundwater. In terms of Poisson’s ratio, the most important and key installations of airport site are located in suitable positions. According to Iranian Seismic Code, most of the lands around the airport are in class 2 and 3. It seems that a fault or a discontinuity is passed from northwest to the southeast of the study area. This site, according to geological, subsurface geophysical, and geotechnical boreholes studies, is high risk-earthquake prone.

Deep characterization of the Santiago Basin using HVSR and cross-correlation of ambient seismic noise

Continuously recorded seismic ambient noise is used to investigate the intermediate and deep structure of the Santiago Basin for seismic site-response evaluation. Single-station H/V spectral ratios (HVSR) were used as a proxy to identify zones with high stiffness soils and low impedance contrast with the underlying bedrock, as a complement of available surface geology information. Frequency-domain cross-correlation of the vertical components of ambient noise were calculated and used to estimate phase velocity dispersion curves associated to station pairs over different soil deposits. In addition, noise correlation functions (NCFs) calculated from time-domain cross-correlation of the vertical seismic noise records were used to estimate group velocity dispersion curves and to verify results from the spectral method. Data processing from both methods resolves a frequency band between 0.1 and 8.0Hz, a critical band for civil infrastructure that is difficult to determine with traditional local-scale passive surface wave methods. Station pairs with high signal correlation over stiff soils in the center, south, and east part of the basin, mainly associated to flat HVSR response, yielded robust phase velocity dispersion curves that vary approximately from 3.5km/s at 0.1Hz to 1km/s at 4Hz. Shear wave velocity profiles inverted from the dispersion curves show high average shear wave velocities that also have a pronounced increase rate with depth and a lack of clear soil-bedrock interface at depths predicted by available gravimetric data.

Ultrasound elastography

Noninvasive, ultrasound-based methods for visualizing and measuring tissue elasticity are becoming more and more common in routine practice. Using hepatic shear wave elastography, cut-off levels can help to detect the degree of relevant fibrosis (F ≥ 2) with a diagnostic accuracy using the area under the reader operating characteristic (AUROC) of 87 % and cirrhosis (F = 4, AUROC 93 %). Normal values virtually exclude liver cirrhosis (negative predictive value up to 97 %) and high shear wave velocities predict complications in the course of primary sclerosing cholangitis, liver cirrhosis and chronic hepatitis B or C. Elastography is of no relevant help in the differentiation of the dignity of hepatic lesions. Concerning thyroid or breast lesions, low shear wave velocities are indicative of benign lesions and in contrast, high velocities of malignant lesions. A differentiation between benign and malignant thyroid nodules is performed by elastography with a sensitivity of 89 % and a specificity of 82 %. In breast lesions a differentiation of nodes can be improved with elastography compared to B-mode ultrasound alone with a sensitivity of 97 % and a specificity of 83 %. Invasive biopsy punctures can therefore be specifically performed or can be omitted. Due to several influencing factors, in particular during liver elastography, the measurements need to be interpreted in the clinical context. In summary, ultrasound-based elastography provides helpful information for the detection of hepatic fibrosis and for further characterization of thyroid or breast lesions in addition to classical techniques, such as B-mode imaging and color Doppler.

Constraining lithologic variability along the Alleghanian detachment in the southern Appalachians using passive-source seismology

Research Article| May 01, 2015 Constraining lithologic variability along the Alleghanian detachment in the southern Appalachians using passive-source seismology E. Horry Parker, Jr.; E. Horry Parker, Jr. 1Department of Geology, University of Georgia, Athens, Georgia 30602, USA Search for other works by this author on: GSW Google Scholar Robert B. Hawman; Robert B. Hawman 1Department of Geology, University of Georgia, Athens, Georgia 30602, USA Search for other works by this author on: GSW Google Scholar Karen M. Fischer; Karen M. Fischer 2Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA Search for other works by this author on: GSW Google Scholar Lara S. Wagner Lara S. Wagner 3Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015, USA Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (5): 431–434. https://doi.org/10.1130/G36517.1 Article history received: 10 Dec 2014 rev-recd: 13 Feb 2015 accepted: 20 Feb 2015 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E. Horry Parker, Robert B. Hawman, Karen M. Fischer, Lara S. Wagner; Constraining lithologic variability along the Alleghanian detachment in the southern Appalachians using passive-source seismology. Geology 2015;; 43 (5): 431–434. doi: https://doi.org/10.1130/G36517.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Polarities and amplitudes of intracrustal P-SV conversions (P waves converted to vertically polarized shear waves) in receiver functions from the Southeastern Suture of the Appalachian Margin Experiment array and USArray Transportable Array provide new constraints on the origin of seismic reflectivity delineating the Alleghanian detachment in the southern Appalachians(eastern United States). Forward modeling of receiver functions is consistent with a 3.5-km-thick, high shear-wave velocity (Vs = 3.9 km/s) section of deformed Paleozoic platform metasedimentary rocks beneath the Blue Ridge at 3–6.5 km depth. In the Inner Piedmont, conversions from the top and base of a low-Vs zone (3.1 km/s) at depths of 5–9 km are interpreted as a package of metasedimentary rocks or a shear zone characterized by radial anisotropy. The detachment continues to the southeast beneath the Carolina terrane, where high-amplitude negative conversions at 10–13 km depth are consistent with arc rocks (Vs = 4.0 km/s) overlying sheared rocks with lower Vs (3.2 km/s). Southeast-dipping conversions at 5–10 km depth mark the boundary between the Inner Piedmont and Carolina terrane. This study demonstrates that relatively high-frequency receiver functions (up to ∼3 Hz), though still lower in frequency than P-wave energy analyzed for reflection profiling (>20 Hz), can provide important links between surface geology and active-source experiments to better constrain models of crustal structure. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Potential use of point shear wave elastography for the pancreas: A single center prospective study

AimClinical use of point shear wave elastography for the liver has been established, however, few studies demonstrated its usefulness for the pancreas. A prospective study was conducted to clarify its feasibility for the pancreas and its usefulness for the identification of high risk group for pancreatic cancer. Patients and methodsConsecutive eighty-five patients underwent point shear wave elastography for the pancreas. The success rate of shear wave velocity (SWV) measurement, that is the number of successful measurements over total 10 measurements, was recorded. The SWV of the pancreas measured at non-tumorous area was compared between patients with and without pancreatic cancer. Factors associated with high SWV were determined by logistic regression model. ResultsSixty patients were included, of these 18 had pancreatic cancer. The success rate of 100% was achieved at the head, the body and the tail of the pancreas in 80%, 83%, and 68% of the patients, respectively. The success rate of ≥80% was achieved in 100%, 100%, and 96% of the patients, respectively. Although mean SWV of the pancreas harboring pancreatic cancer tended to be higher compared with that of the pancreas without cancer (1.51±0.45m/s vs 1.43±0.28m/s), they did not reach statistical significance. Multivariate analysis showed that increased amount of alcohol intake was associated with high SWV. ConclusionThe SWV of the pancreas was measured with excellent success rate. However, tendency of higher SWV obtained from the pancreas harboring pancreatic cancer needed to be further investigated.