High Shear Wave Velocity Research Articles

Effective elastic thickness variations along the Andean margin and their relationship to subduction geometry

We present a new map of the spatial variations in effective elastic thickness, Te, along the Andes estimated using Bouguer coherence. The Te variations reflect interactions between subducting slab and preexisting terrane structure. In the forearc, conductive cooling of the continent by the subducting slab exerts primary control on rigidity, resulting in Te that is highest (∼40 km) where the oceanic lithosphere is oldest and coldest (∼20°S). In the central Andes, Te is relatively low (∼20 km) along the volcanic chain and the Altiplano and Puna plateaus. We interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes, a shallow and hot asthenosphere, and a very weak lower crust throughout this region. East of the plateaus, high Te delineates underthrusting of the Brazilian shield. Finally, north and south of the plateaus, flat subduction areas are characterized by high Te, high shear wave velocity, thick thermal lithosphere, and low heat flow, indicating that continental lithosphere there is thicker, colder, and stronger. On the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere. In particular, we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge, which control the suction moment responsible for the subduction angle at depths ≥70–100 km. For example, when oceanic lithosphere subducts beneath thin continental lithosphere, the low‐viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles. However, when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere, the asthenospheric wedge narrows and corner flow drags high‐viscosity mantle from the base of the thick (>150 km), cold continent into the wedge. Suction forces increase with both narrowing of the wedge and its increasing viscosity. We estimate the asthenospheric viscosity underneath thick, cold continents to be ≥1020 Pa s, sufficient to induce flat subduction. Later, after prolonged hydration and weakening of the continent's base, asthenospheric flow into the wedge may resume, allowing the slab to sink again into the mantle at normal angles.

Site Classification Using Horizontal-to-vertical Response Spectral Ratios and its Impact when Deriving Empirical Ground-motion Prediction Equations

We classify sites based on their predominant period computed using average horizontal-to-vertical (H/V) response spectral ratios and examine the impact of this classification scheme on empirical ground-motion models. One advantage of this classification is that deep geological profiles and high shear-wave velocities are mapped to the resonance frequency of the site. We apply this classification scheme to the database of Fukushima et al. [2003], for which stations were originally classified as simply rock or soil. The calculation of average H/V response spectral ratios permits the majority of sites in the database to be unambiguously classified. Soft soil conditions are clearly apparent using this technique. Ground-motion prediction equations are then computed using this alternative classification scheme. The aleatoric variability of these equations (measured by their standard deviations) is slightly lower than those derived using only soil and rock classes. However, perhaps more importantly, predicted response spectra are radically different to those predicted using the soil/rock classification. In addition, since the H/V response spectral ratios were used to classify stations the predicted spectra for different sites show clear separation. Thus, site classification using the predominant period appears to be partially mapped into the site coefficients of the ground-motion model.

Effective elastic thickness of South America and its implications for intracontinental deformation

The flexural rigidity or effective elastic thickness of the lithosphere, Te, primarily depends on its thermal gradient and composition. Consequently, maps of the lateral variability of Te in continents reflect their lithospheric structure. We present here a new Te map of South America generated using a compilation of satellite‐derived (GRACE and CHAMP missions) and terrestrial gravity data (including EGM96 and SAGP), and a multitaper Bouguer coherence technique. Our Te maps correlate remarkably well with other proxies for lithospheric structure: areas with high Te have, in general, high lithospheric mantle shear wave velocity and low heat flow and vice versa. In this paper we focus on the Te of the stable platform. We find that old cratonic nuclei (mainly Archean and Early/Middle Proterozoic) have, in general, high Te (>70 km), while the younger Patagonian Phanerozoic terrane has much lower Te (20–30 km), suggesting that Te is related to terrane age as has already been noted in Europe. Within cratonic South America, Te variations are observed at regional scale: relatively lower Te occurs at sites that have been repeatedly reactivated throughout geological history as major sutures, rift zones, and sites of hot spot magmatism. Today, these low Te areas are surrounded by large cratonic nuclei. They concentrate most of the intracontinental seismicity and exhibit relatively high surface heat flow and low seismic velocity at 100 km depth. This implies that intracontinental deformation focuses within relatively thin, hot, and hence weak lithosphere, that cratonic interiors are strong enough to inhibit tectonism, and that the differences in lithospheric rigidity, structure, and composition between stable cratons and sites of intracontinental deformation are not transient, and may have been maintained, in some cases, for at least 500 m.y.

Liquefaction evaluation discrepancies in tropical lagoonal soils

Field penetration tests and shear wave velocity measurements are both established and accepted methods for evaluating liquefaction potential in soils. The results produced by the two methods are generally well correlated. However, recent studies have shown that when investigating tropical lagoonal deposits, the same accepted methods for evaluating liquefaction potential often produce significant discrepancies in results. This discrepancy is most apparent in saturated lagoonal deposits of calcareous gravelly sand (or sandy gravel), which tend to exhibit low penetration resistance values but relatively high shear wave velocities. These disparate test results can suggest different soil classifications under current building codes. Ambiguity in the code may allow for a potentially unconservative classification, which may in turn allow for the use and construction of less costly, lighter weight foundation systems than warranted. Equally as important, the potential for unconservative design as related to liquefaction appears to be high when shear wave velocity measurements are used as a basis for evaluation in these types of lagoonal deposits. Because of this, it is strongly recommended that caution should be excercised when determining seismic design parameters in these types of geologic environments. A hypothesis to explain the discrepancies in the results of evaluation methods and a suggested design protocol is proposed.

Shear wave velocity monitoring of collapsible loessic brickearth soil

Metastable loessic brickearth comprises a stiff fabric structure with inter-particle interactions different to those normally associated with clay-sized or silt-sized particle fabrics. Laboratory samples loaded near in situ moisture contents exhibited little consolidation and relatively high shear wave velocities, which changed in response to sample flooding. In situ hydro-collapse caused non-monotonic changes in the velocity of shear waves through loessic brickearth that was subjected to simple flooding and to flooding while under additional surface loading. Hydro-collapse in situ resulted in an overall reduction of up to 50% in the shear wave velocity. A conceptual model of brickearth structure based on SEM images is presented to explain the process of collapse and its effect on shear wave velocity. These indicate a transition from a relatively low-density, high-stiffness fabric to the higher-density, lower-stiffness fabric during structural collapse of the loessic brickearth. The collapse process disrupts clay bridge-bonds that hold individual and aggregated clay-coated silt sized particles in an open packed structure, and which are absent in a more closely packed collapsed structure. These studies provide information for geohazard research and the development of shear wave velocity and other geophysical tools to assess soil collapse potential in situ .

VS30mapping and soil classification for seismic site effect evaluation in Dinar region, SW Turkey

SUMMARY The Dinar earthquake (M S = 6.1) of 1995 October 1 killed 90 people and destroyed more than 4000 buildings. Despite the moderate size of the earthquake, the level of damage was extremely high, which led to many studies that were carried out in the region. The majority of these studies concluded that the main reasons for the damage were the construction errors and the poor soil conditions. However, at that time no appropriate soil condition map based on extended, high density measurements was available. Shear wave velocity is an important parameter for evaluating the dynamic behaviour of soil in the shallow subsurface. Thus site characterization in calculating seismic hazards is usually based on the near surface shear wave velocity values. The average shear wave velocity for the top 30 m of soil is referred to as V S 30 . For earthquake engineering design purposes, both the Uniform Building Code (UBC) and Eurocode 8 (EC8) codes use V S 30 to classify sites according to the soil type. The V s 30 values calculated by using multichannel analysis of surface waves (MASW) were used to create a new soil classification map of the Dinar region. Surface seismic measurements were carried out at 50 locations mostly in Dinar city and its surroundings. The dispersion data of the recorded Rayleigh waves were inverted using a Genetic Algorithm (GA) method to obtain shear wave velocity profiles of the investigated sites. Thus the derived V s 30 map of the Dinar region was transformed to the UBC and EC8 standards. Soil classification results show that most parts of the region, located in alluvial basin, have low shear wave velocity values. These values are within the range of 160–240 m s −1 and thus fall into the S D and S E categories according to the UBC and the C and D categories according to EC8. Within the region, some parts located on the hill zone and the transition zone have better soil conditions [corresponding to S C (UBC) and B (EC8) categories] and have comparatively high shear wave velocities in the range of 500–740 m s −1 and 350–450 m s −1 , respectively. V S 30 and soil classification maps were compared with the damage distribution associated with the earthquake. In possession of a detailed shear wave velocity map of Dinar City, in general, the results show that there is a correlation between the V S 30 values and the damage distribution of the region. In addition to the low V S 30 values, the likely causes of the damage were investigated, and it is observed that one of the major factors for high levels of damage is 3-D variations of geological structures.

Toward Seismic Microzonation—2-D Modeling and Ambient Seismic Noise Measurements: The Case of an Embanked, Deep Alpine Valley

In the Sion area of Switzerland, part of a deep, embanked sediment-filled valley, investigations on soil site effects have been conducted using two independent methods. Two-dimensional (2-D) modeling was performed with a program based on the Indirect Boundary Element Method (Pedersen et. al. 1994). Numerical simulations allow taking into account the subsurface geometry of the valley and its peculiar characteristics, such as a variable shape ratio and a high shear-wave velocity contrast. The H/V method has been applied on ambient seismic noise measurements recorded on sites as close as possible to the 2-D modeling. This technique allows capturing the fundamental resonant frequency of the deepest sediments as well as identifying the existence of a surficial deposit. Both approaches agree on the fact that the fundamental resonant frequency of the valley is below 1 Hz. The amplification level of the predominant frequency obtained with numerical simulation is up to two times higher than the one given by the H/V ratio. These results provide the basis for further investigations in order to resolve differences.

Rayleigh-Wave Group-Velocity Studies beneath the Indian Ocean

The fundamental mode Rayleigh wave generated by 16 earthquakes, which occurred in the Indian Ocean and were recorded at 14 seismic stations of Asia, Africa, and Australia, are analyzed to estimate the Rayleigh-wave group velocity at periods of 10 to 60 sec by using the multiple filter analysis technique. In addition to this, Rayleigh-wave group-velocity data available in the literature across different propagation paths of the Indian Ocean forming a dense distribution of seismic wave traverses have been considered for tomographic studies. The group-velocity distribution maps have been obtained at periods of 10, 20, 30, 40, 50, and 60 sec for the Rayleigh wave. The minimum value of the group velocity of 2.0 km/sec is centered near the Rodriguez triple junction (25° S, 70° E) at 10 sec and higher value (3.4–4.0 km/sec) at 20 sec and greater period. As we move in the north-northwest direction from the Rodriguez triple junction, the Rayleigh-wave group-velocity isolines at 10 and 20 sec are also increasing in the northern direction in both the east and west sides of the ridge axis. Another minimum value of group-velocity isolines (1.9 km/sec) is centered near (25° S, 90° E) at 10 sec, and there is a gradual increase in the northern direction across the Ninetyeast Ridge. These observations are in accordance with the increase in the age of the ocean floor and there is a gradual increase in the group-velocity isolines. This can be interpreted as due to the hot uprising convection current, the material shows low shear-wave velocity along the ridge axis, and farther away from the ridge axis the material has become cooler with higher shear-wave velocity. The inversion of Rayleigh-wave group-velocity across the Ninetyeast Ridge shows 120-km-thick lvz (low-velocity zone) of shear-wave velocity of 4.38–4.78 km/sec at a depth of 40 km from the water surface, whereas other parts of the Indian Ocean show 44-km-thick lvz with shear-wave velocity of 4.12–4.17 km/sec at a depth of 40 km from the water surface. The high shear-wave velocity below Moho (4.19–4.75 km/sec) beneath the Ninetyeast Ridge indicates the presence of a cold and dense lithosphere beneath it.

Mineralogy and elasticity of the oceanic upper mantle: Origin of the low‐velocity zone

We use a new method to construct an upper mantle model based on self‐consistent computation of phase equilibria and physical properties. Computation of the isotropic elastic wave velocities of a pyrolytic bulk composition in thermodynamic equilibrium shows a distinct low‐velocity zone with a minimum velocity VS = 4.47 km s−1 along the 100 Ma geotherm. In the vicinity of the low‐velocity zone the velocity of this null hypothesis is approximated along oceanic geotherms by VS = 4.77 + 0.0380(P, z/29.80) − 0.000378(T − 300), with pressure P in GPa, depth z in km, temperature T in K, and velocity VS in km s−1. The null hypothesis predicts a minimum VS 0.1–0.2 km s−1 higher than that in seismological models of 100 Ma Pacific. We find that dispersion, estimated solely on the basis of seismological attenuation models, can account for this residual velocity deficit. Except in the immediate vicinity of the ridge (t < 5 Ma), a solid‐state low‐velocity zone provides a satisfactory quantitative explanation of seismic observations. We do not find a satisfactory explanation for the magnitude of the Gutenberg discontinuity or for the high shear wave velocity gradient zone.

Comparing Intensity Variation of the 2001 Nisqually Earthquake with Geology in Victoria, British Columbia

This article compares the variation in observed intensity of the 2001 M W 6.8 Nisqually, Washington, earthquake in Victoria, British Columbia (150 km from the epicenter), with amplification hazard predictions based on the average shear-wave velocity of geologic units. Modified Mercalli intensities were assigned from 750 felt reports collected by online Web submission augmented by door-to-door canvassing in regions of particular interest. An intensity map was created based on high-resolution (sub-city block) georeferencing with the Canadian postal code system. Site-specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear-wave velocity substrates (bedrock and glacial till versus soft clay and peat). Overall, the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear-wave velocities across greater Victoria.

Shear wave structure from joint analysis of seismic and seafloor compliance data

SUMMARY Determining shear wave structure is the key to identifying the amount and location of fluid within the crust. Seismic and seafloor compliance methods provide independent estimates of shear wave structure, and a joint analysis of the two data sets should provide better constraints on the properties of the uppermost oceanic crust. We consider an example from 9 ◦ 33 � N on the East Pacific Rise. Seismic data from an on-axis expanding spread profile have been reanalysed to determine a shear wave structure for layer 2B; pS arrivals require a high shear wave velocity within this layer (Poisson ratio in the range 0.22‐0.25). Compliance data from the same location are seemingly inconsistent with this result, requiring that layer 2B is a region of low shear wave velocity (Poisson ratio in the range 0.33‐0.44). The quantitative differences between the two results can be explained by anelasticity and anisotropy; conversely, a knowledge of this discrepancy can be used to constrain the attenuation structure.

African hot spot volcanism: small-scale convection in the upper mantle beneath cratons.

Numerical models demonstrate that small-scale convection develops in the upper mantle beneath the transition of thick cratonic lithosphere and thin oceanic lithosphere. These models explain the location and geochemical characteristics of intraplate volcanos on the African and South American plates. They also explain the presence of relatively high seismic shear wave velocities (cold downwellings) in the mantle transition zone beneath the western margin of African cratons and the eastern margin of South American cratons. Small-scale, edge-driven convection is an alternative to plumes for explaining intraplate African and South American hot spot volcanism, and small-scale convection is consistent with mantle downwellings beneath the African and South American lithosphere.

Three-dimensional shear wave velocity structure in the upper mantle beneath the Philippine Sea region

The three-dimensional shear wave velocity structure in the upper mantle beneath the Philippine Sea was investigated with Rayleigh wave phase velocities in the periods 30–100 s. More than 900 Rayleigh wave phase velocity curves were obtained for this region with good path coverage. The phase velocity data were inverted for the phase velocity distribution maps in the Philippine Sea with 2-D tomographic technique without any a priori regionalization. The resolutions of the tomographic analysis were quite good in almost of the target region. The phase velocity maps were inverted for the 3-D shear wave velocity structure in the upper mantle down to 220 km. In the shallow depths lateral heterogeneities with short wavelength were seen in the shear wave velocity maps. This might be related with complicated surface structures. In the middle depths the shear wave velocity was well correlated to the main tectonic features seen at the surface and well explained by the evolution history of the Philippine Sea. The older western Philippine Sea had higher shear wave velocities than the younger eastern Philippine Sea. In the western Philippine Sea the central basin ridge, which is the youngest in this area, showed the low velocity anomaly. This is supported by the fact that the West Philippine Basin was formed in this area. In the depths 150–200 km the low velocity anomaly was dominant inside the Philippine Sea, which might suggest the existence of the mantle return flows. The thickness of the lithosphere in the south of the West Philippine Basin reached about 100 km, which is much thicker than the results of previous studies for this region.

Färoe‐Iceland Ridge Experiment 2. Crustal structure of the Krafla central volcano

The seismic velocity structure of the Krafla central volcano is characterized by large variations in compressional velocity. A 40 km wide high‐velocity dome extends from the lower crust (11–14 km depth) beneath the volcano narrowing upward. A magma chamber sits at its top near 3 km depth. It is defined by both 0.2–0.3 s compressional wave delays and shear wave shadowing to be 2–3 km N‐S, 8–10 km E‐W, and 0.7–1.8 km thick. The near‐surface structure (uppermost 2.5 km) of the Krafla caldera is approximately flat‐lying, with only minor lateral heterogeneities. The crust beneath the magma chamber has low shear wave attenuation and anomalously high compressional and shear wave velocities. Shear waves, reflected from a 19 km deep Moho, are clearly visible for some paths through the crustal volume below the magma chamber, even though the more shallow diving S waves are severely attenuated. The midcrust beneath the shallow magma chamber cannot contain partial melt or even be at near‐solidus temperatures. The Krafla central volcano plays a major role in crustal genesis along the plate boundary. The high‐velocity dome, in our view, represents crust generated in and around the magma chamber, which has subsequently been advected to greater depths.

Deep Seismic Expression of an Ancient Plate Boundary in Europe

Seismological results on the structure of the upper mantle below Europe reveal a marked contrast in seismic properties between Precambrian and younger parts of Europe. The Precambrian craton in eastern Europe is characterized by high shear-wave velocities, which can be explained by low temperatures. The transition to low seismic velocities below Phanerozoic Europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers. Despite the long and complex tectonic history of the plate boundary zone, the transition is remarkably sharp, which rules out any significant lateral transport of asthenospheric material across the suture zone.

Shear wave velocity structure over the eastern Indian subcontinent

Fundamental-mode surface wave generated by twelve earthquakes, which occurred in northeastern India and nearby regions and were recorded at the Shillong (SHL) and Chiengmai (CHG) seismic stations are used to determine the shear wave velocity structure beneath these regions. The Frequency Time Analysis method is used to determine the group velocities for periods ranging from 4 to 50 s for fundamental-mode Rayleigh and Love waves. A high shear wave velocity (4.2–4.7 km s −1) is estimated in the lower 30–34 km of the crust. Crustal thickness is found to vary from 36 to 56 km with an overlying 2–4 km sedimentary thickness of shear wave velocity of 2.55–2.75 km s −1. The shear wave velocity in the upper 10 km of crust is 3.5–3.7 km s −1 below the sedimentary layer. The inferred high shear velocity for the lower crust beneath these regions suggests an oceanic affinity and they are different from the Indian shield structure. The lower crust must have an oceanic origin as derived from the reminiscent of a certain oceanic lithosphere. The available data do not permit us to estimate the upper mantle structure precisely; however, it shows a higher upper mantle shear velocity of 5.1–5.3 km s −1. This may be indicative of active tectonism beneath these regions in the uppermost mantle. The Moho boundary is not sharply defined here. The increase in crustal thickness may be due to the collision of the Indian and Eurasian plates in the north and subduction of the Indian plate beneath the Burmese Arc in the east.

Analysis of the January 26th, 1985, Mendoza (Argentina) earthquake effects and of their possible correlation with the recorded accelerograms and soil conditions

An analysis was made of the distribution of effects produced by Mendoza (Argentina) earthquake of January 26, 1985 ( m b = 6.0), which affected one of the most important urban agglomerates of western Argentina, housing more than 800,000 inhabitants. The epicenter was located at distances of 15 and 50 km from the closest and farthest ends of the urban area, respectively. Damage distribution was not uniform. Some small areas reached a maximum intensity of VIII MM. Damage indexes were defined from the information provided by damage surveying. These indexes relate the degree of damage suffered by adobe constructions with respect to the total number of them. Also, the distribution of damaged constructions as a function of their age was analyzed. Many strong motion records were obtained during this earthquake. Five accelerograms were recorded at sites located in the highly populated area. Several seismoscope records were also obtained, some of them at the same sites as the accelerograms. Peak ground accelerations in Gran Mendoza varied between 0.10 and 0.41 g. The analysis of all these records gave information on spectral acceleration, spectral amplification and prevailing periods. Two types of subsoil conditions prevail in the area studied: shallow, stiff soils and deep soils. The former are soils with less than 20 m of depth to the high shear wave velocity materials, while the latter have more than 20 m to that material. The spatial distribution of both types of soils was accurately known from the information provided by many drillings and several surface geophysical measurements. This knowledge allowed the soil types to be relate with damage distribution and strong motion record parameters. The results obtained show no relation between damage intensities and subsoil conditions. The best example of this conclusion was observed in the two places where higher intensities were recorded in agreement with the higher values of peak accelerations, while the subsoil conditions were completely different. However, a fairly good relation was obtained between intensity of damage and age of the construction.

Small scale lateral variability of geoacoustic properties of the upper 40 m of the seafloor

The spectral response versus grazing angle of the seafloor sediment for several kilometers of deep towed, multichannel seismic reflection data from Atlantic seafloor near the Blake outer ridge shows variations of as much as 15 to 20 dB in bottom loss over distances of less than 50 m. A video of this spectrum versus offset (SVO) data, which explicitly shows the lateral variations as the DTAGS instrument is towed along just above the seafloor, is presented. A few regions of anomalously high shear wave velocities also are identified in these observations. These data demonstrate that a seemingly smooth seafloor can be a rough, frequency-dependent scattering surface. [This work is supported by the Office of Naval Technology.]

Shear wave reflectivity, anisotropies, Poisson's ratios, and densities of a southern Appalachian Paleozoic sedimentary sequence

The physical properties of a sequence of Paleozoic sedimentary rocks have been examined in detail, with an emphasis on laboratory measurements of density, shear wave velocity, shear wave splitting, and V p / V s ratios. Seismic properties of 147 cores from 49 rock samples collected from the Thorn Hill sedimentary sequence of eastern Tennessee are examined in terms of implications for future seismic studies in the southern Appalachians. The shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz. Shear wave velocity anisotropy is present in most of the lithologic groups; it is highest in the shales while being almost insignificant in the dolostones. The related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation. Splitting, due to preferred mineral orientation, is most prominent in the shales, but also is significant in some of the carbonates. Compressional to shear velocity ( V p / V s ) ratios of approximately 1.82 (dolostones) and 1.95 (limestones) effectively characterize the carbonates while other lithologies display wider ranges of V p / V s , primarily due to the influence of accessory minerals such as quartz. Densities of the sample suite range from 2.34 g/cm 3 (shale) to 2.86 g/cm 3 (dolostone). Using average data for each lithologic group to calculate normal-incidence reflection coefficients, significant differences in the shear and compressional reflectivity of hypothetical interfaces are found. Normal-incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire Thorn Hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327-m-thick sequence. Overall, the shear and compressional synthetics are similar in appearance. Differences are seen at some interfaces in the Mississippian-Devonian interval, which are more reflective to shear waves, and in the Ordovician Martinsburg Formation, which appears more reflective to compressional waves.

Lateral variability of geoacoustic properties of the seafloor.

Using deep towed, multichannel seismic reflection data, the spectral response of the seafloor sediment as a function of offset or grazing angle along several kilometers of old Atlantic seafloor near the Blake outer ridge has been measured and variations of as much as 15 to 20 dB in bottom loss over distances of less than 50 m have been found. A video will be shown of this spectrum versus offset (SVO) data that explicitly shows the lateral variations as the DTAGS instrument is towed along just above the seafloor. A few regions of anomalously high shear wave velocities also will be pointed out. These data demonstrate that a seemingly smooth seafloor can be a rough, frequency-dependent scattering surface. [This work is supported by the Office of Naval Technology.]