Crustal Seismic Velocity Research Articles

Continental Residual Topography Extracted From Global Analysis of Crustal Structure

AbstractContinental topography is dominantly controlled by a combination of crustal thickness and density variations. Nevertheless, it is clear that some additional topographic component is supported by the buoyancy structure of the underlying lithospheric and convecting mantle. Isolating these secondary sources is not straightforward, but provides valuable information about mantle dynamics. Here, we estimate and correct for the component of topographic elevation that is crustally supported to obtain residual topographic anomalies for the major continents, excluding Antarctica. Crustal thickness variations are identified by assembling a global inventory of 26,725 continental crustal thickness estimates from local seismological data sets (e.g., wide‐angle/refraction surveys, calibrated reflection profiles, receiver functions). In order to convert crustal seismic velocity into density, we develop a parametrization that is based upon a database of 1,136 laboratory measurements of seismic velocity as a function of density and pressure. In this way, 4,120 new measurements of continental residual topography are obtained. Observed residual topography mostly varies between ±1 and 2 km on wavelengths of 1,000–5,000 km. Our results are generally consistent with the pattern of residual depth anomalies observed throughout the oceanic realm, with long‐wavelength free‐air gravity anomalies, and with the distribution of upper mantle seismic velocity anomalies. They are also corroborated by spot measurements of emergent marine strata and by the global distribution of intraplate magmatism that is younger than 10 Ma. We infer that a significant component of residual topography is generated and maintained by a combination of lithospheric thickness variation and sub‐plate mantle convection. Lithospheric composition could play an important secondary role, especially within cratonic regions.

Spatial variation of crustal seismic velocity and Poisson’s ratio in the Jiangsu-South Yellow Sea area: Implication for seismotectonics

Spatial variation of crustal seismic velocity and Poisson’s ratio in the Jiangsu-South Yellow Sea area: Implication for seismotectonics

Evaluation of 3D crustal seismic velocity models in southwest China: Model performance, limitation, and prospects

Evaluation of 3D crustal seismic velocity models in southwest China: Model performance, limitation, and prospects

Upper crustal seismic velocity structure of the Hayward fault zone, San Francisco Bay, California, USA: Results from the 2016 East Bay Seismic Experiment (EBSI-16)

We developed Vp, Vs, Vp/Vs ratio, and Poisson’s ratio models of the uppermost crust (<4 km depth) from the eastern San Francisco (SF) Bay (California, USA) to near the Calaveras fault along a 15-km-long, linear profile. Upper crustal velocities are highly variable beneath, west, and well east of the Hayward fault. We observe eight notable features, from west to east: (1) Near San Francisco Bay, there is an ∼2-km-wide structure with high Vp/Vs ratios (up to 5) and Poisson’s ratios (up to 0.48) extending from the surface to the base of our model, which we suggest the structure is a near-vertical fault that lies along a straight-line projection between the Silver Creek fault to the south and the Point Richmond fault to the north. The structure may be part of an ∼90-km-long fault along the eastern SF Bay. (2) The western East Bay Plain, the lower lying area between the bay and the hills, includes up to 800 m of low-velocity sediments (Vp ∼1600−3000 m/s, Vs ∼500 m/s to ∼1000 m/s), underlain by higher velocity basement rocks (Vp ∼3000−5800 m/s; Vs ∼1000−1500 m/s). (3) Between ∼1 km and 3 km east of the Bay shoreline, sediments thin in a series of steps (likely faults) toward the Hayward fault. (4) Between ∼3 km west and ∼1 km east of the Hayward fault (at the East Chabot fault) at depths greater than 1 km, basement Vp (up to 6000 m/s) and Vs (up to 2800 m/s) are high, and Vp/Vs ratios (<2) and Poisson’s ratios (<0.3) are low, suggesting crystalline rocks. Furthermore, a near-vertical zone of low Vp/Vs ratios and Poisson’s ratios is between near-surface traces of the Hayward and East Chabot faults, likely corresponding to the San Leandro Gabbro of Ponce et al. (2003). (5) Eastward of the East Chabot fault in the upper 1.5 km, basement Vp (∼3000 m/s to ∼4200 m/s) and Vs (∼1200−2000 m/s) are lower than those west of the fault. (6) In the eastern Hayward/Oakland Hills, there are zones of laterally varying, high- and low-velocity (Vp ∼2500−3000 m/s) Jurassic−Cretaceous and Tertiary sediments in the shallow subsurface that likely extend much deeper than imaged. (7) Seismic energy that propagates westward from sources east of the Hayward fault (HF) appear weaker than energy that propagates eastward from sources west of the HF, suggesting that the HF acts as a partial barrier to shallow seismic energy propagation into the more populated eastern SF Bay area. (8) Unlike many fault zones, it appears that the active trace of the Hayward fault (in our study area) is not cored by a prominent, low-velocity zone relative to rocks to the east and west of the active trace. However, the active trace does mark a prominent change from relatively higher velocities to the west and lower velocities to the east.

1D Seismic Velocity Models for West-Central and Western Montana

Abstract In seismically active areas with infrequent large-magnitude earthquakes, high-quality seismic data are critical for determining accurate seismic velocity models. Here, we present a new local-scale crustal seismic velocity model in west-central Montana as well as a new regional-scale crustal and upper mantle seismic velocity model for broader western Montana. These models are constrained by phase arrivals from several seismic networks, including the University of Montana Seismic Network, the Montana Regional Seismic Network, the Advanced National Seismic System, temporary deployments by the U.S. Geological Survey, and the USArray Transportable Array. We jointly invert for hypocenters and velocity structure using the VELEST software. The local seismic velocity model is the first model specific to west-central Montana, using P-wave arrivals from aftershocks of the 2017 M 5.8 Lincoln, Montana, earthquake. The local model consists of eight layers down to 30 km depth below the mean sea level and spans a region of approximately 40,​000 km2 (200 km × 200 km). The velocity of the uppermost layer in the local model is 4.80 ± 0.11 km/s, and the velocity of the lowermost layer resolved from the data is 7.00 ± 0.05 km/s. Using an expanded dataset across a broader geographical area, we develop a “regional” seismic velocity model that represents spatially averaged velocity structure across western Montana. The regional model consists of thirteen layers down to 45 km depth below the sea level and is appropriate to an area of 160,​000 km2 (400 km × 400 km). The velocity of the uppermost layer is 4.30 ± 0.15 km/s, and the velocity of the lowermost layer is 8.00 ± 0.04 km/s. The new models are similar to prior velocity models for western Montana, but feature improved vertical resolution of layer velocities.

Different Martian Crustal Seismic Velocities Across the Dichotomy Boundary From Multi‐Orbiting Surface Waves

AbstractWe have observed both minor‐arc (R1) and major‐arc (R2) Rayleigh waves for the largest marsquake (magnitude of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two‐layer model with an interface located at 21–29 km and an upper crustal shear‐wave velocity of 3.05–3.17 km/s can fit the group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models constrained from gravity data and upper crustal shear‐wave velocities of 2.61–3.27 and 3.28–3.52 km/s in the lowlands and highlands, respectively. The shear‐wave velocity being faster in the highlands than in the lowlands indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.

India-Antarctica collisional ridge structure below Nellore Schist and Eastern Ghats Belts as revealed by seismic studies

In Columbia, Rodinia and Gondwana supercontinental assembly periods, eastern margin of India lay quite close to the east Antarctica. During these periods, this region underwent prolonged sedimentation, magmatism, oceanic subduction, multiple accretion and continent-continent collision which have left their imprints in the geological and geophysical observations. In the present study, we have analyzed crustal seismic velocity structure along the DSS profiles located in the eastern part of the Indian shield that cuts across the Proterozoic Cuddapah Basin, Godavari and Mahanadi Gondwana grabens. The study revealed presence of a prominent high velocity (6.2-6.5 km/s) hidden ridge structure, which is 30 to 50 km wide and located at a shallow subsurface depth beneath the Nellore Schist Belt and Eastern Ghats Belt. It underlies below Kaligiri-Duttaluru along the Kavali-Parnapalle profile, Darsi-Addanki along the Alampur-Koniki-Ganapeswaram profile and Sattupalli-Ashwaraopet in Kallur-Polavaram profile. This ridge structure is conspicuously characterized by high gravity anomaly gradients from -90 to -15 mGal. Gravity patterns over these regions further indicate that this ridge which appears to continue from the north of Chennai to Bhavanipatna region in Bastar Craton, may have been formed due to the collision of East Antarctic terrain with eastern Indian Shield after the cessation of supra-subduction at the end of Mesoproterozoic. Further, this ridge structure is flanked by Proterozoic sediments on either side; in Cuddapah Basin on its western side and East Coast Sedimentary Basin on its eastern side, which together with the possible occurrence of Proterozoic sediments in other basins, would indicate that the extent of Proterozoic sedimentation was much larger than hitherto known. We suggest that this region was rifting during Paleo-Mesoproterozoic period and possibly a shallow marine basin existed, when it was an integral part of the Columbia supercontinent assembly. It underwent another rifting phase and denudation during the Gondwana period as indicated by thin patches of Gondwana sediments which are lined up all along the east coast. Quite likely, the rifting between India and Antarctica during the Gondwana super assembly period initiated in the Permo-Triassic Gondwana period itself, with final separation taking place much later during early Cretaceous period.

Delineation of detailed crustal seismic velocity structure and Moho depths in the Hyderabad region, eastern Dharwar craton, India

Delineation of detailed crustal seismic velocity structure and Moho depths in the Hyderabad region, eastern Dharwar craton, India

Moment Tensor Solutions for Earthquakes in the Southern Korean Peninsula Using Three-Dimensional Seismic Waveform Simulations

Precise estimates of earthquake source properties are crucial for understanding earthquake processes and assessing seismic hazards. Seismic waveforms can be affected not only by individual event properties, but from the Earth’s interior heterogeneity. Therefore, for accurate constraints on earthquake source parameters, the effects of three-dimensional (3D) velocity heterogeneity on seismic wave propagation need evaluation. In this study, regional moment tensor solutions for earthquakes around the southern Korean Peninsula were constrained based on the spectral-element moment tensor inversion method using a recently developed high-resolution regional 3D velocity model with accurate high-frequency waveform simulations. Located at the eastern margin of the Eurasian plate, the Korean Peninsula consists of complex geological units surrounded by thick sedimentary basins in oceanic areas. It exhibits large lateral variations in crustal thickness (> 10 km) and seismic velocity (>10% dlnVs) at its margins in the 3D model. Seismic waveforms were analyzed from regional earthquakes with local magnitudes > 3.4 that occurred within and around the peninsula recorded by local broadband arrays. Moment tensor components were inverted together with event locations using the numerically calculated Fréchet derivatives of each parameter at periods ≥ 6 s. The newly determined solutions were compared with the results calculated from the one-dimensional (1D) regional velocity model, revealing a significant increase in a double-couple component of > 20% for earthquakes off of the coastal margins. Further, compared to initial solutions, ≤ 5 km change in depth was observed for earthquakes near the continental margin and sedimentary basins. The combination of a detailed 3D crustal model and accurate waveform simulations led to an improved fit between data and synthetic seismograms. Accordingly, the present results provide the first confirmation of the effectiveness of using 3D velocity structures for accurately constraining earthquake source parameters and the resulting seismic wave propagation in this region. We suggest that accurate 3D wave simulations, together with improved source mechanisms, can contribute a reliable assessment of seismic hazards in regions with complex continental margin structures and sedimentary basins from offshore earthquakes whose seismic waveforms can be largely affected by 3D velocity structures.

Arclogite nature of the Colombian Andes magmatic arc root: A receiver-function approach

Arclogites are an important part of the continental arc root architecture. When overlooked, the crustal structure could be misinterpreted, assuming that the seismically defined Moho necessarily coincides with the crust-mantle boundary. Evaluating the possible presence of lower crustal rocks below the seismic Moho with physical properties resembling those of the underlying mantle, is therefore, of major importance. Through a multi-approach receiver function assessment, which includes shear wave velocity inversion, and determination of plausible crustal seismic velocity distributions from forward modeling, we present new constraints on the seismic structure of the arc root beneath the Colombian Andes magmatic arc. Results suggest a high-velocity arc root with a latitudinally variable thickness, from 13.5 to 20 km. The arc root is composed of a 4 to 6 km thick upper domain with seismic wave speeds 5% slower, and 8.5 to 14 km thick lower domain 5% faster, relative to the underlying uppermost mantle. This lower crustal structure, coupled with documented garnet pyroxenitic xenoliths, supports an arclogite nature for the Colombian Andes arc root.

Crustal Structure of the Incoming Iquique Ridge Offshore Northern Chile

AbstractThe Peru‐Chile subduction zone hosts M > 8 earthquakes as well as multiple ridges on the downgoing Nazca plate, making this region well suited for investigating the formation, evolution, and potential impacts of subducting features on seismogenesis. To evaluate the physical properties and structural variability of the Iquique Ridge offshore northern Chile, we present a P wave velocity model of the Nazca plate and Iquique Ridge outboard of the 2014 M 8.1 Iquique earthquake sequence. 2D tomographic inversions of P wave traveltime data from the 2016 PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source) controlled‐source experiment indicate that the Iquique Ridge is characterized by significant crustal thickening relative to typical Nazca plate oceanic crust, with a maximum thickness of ∼13 km beneath the most prominent portion of the Iquique Ridge and outer rise. Reduced upper crustal seismic velocities extend from the ridge eastward to the trench, which may indicate increased fracturing and/or hydration during plate bending. Corresponding multi‐channel seismic reflection data show along‐profile structural variation as well, including an intermittent Moho reflector near the onset of crustal thickening and faulting along the landward slope. The structural heterogeneity entering the Peru‐Chile Trench has potential implications for slip behavior at depth assuming that the anomalous crustal structure continues beneath the forearc. We suggest that the increased buoyant normal force associated with discrete subducted Iquique Ridge seamounts similar to the zone of thick crust imaged here could lead to localized increased interplate coupling, while entrained sediment and fractured/altered crust could facilitate aseismic slip.

Decade-long monitoring of seismic velocity changes at the Irpinia fault system (southern Italy) reveals pore pressure pulsations

Several studies have monitored crustal seismic velocity changes and attempted to relate them to the stress state and physical properties in volume embedding fault systems. The aim is to provide constraints on fault system dynamics and earthquake triggering mechanisms. Here, we reconstruct the spatiotemporal (4D) seismic velocity images of volume embedding the Irpinia fault system (IFS, South Italy), which originated the 1980 Ms 6.9 multi-segmented ruptures. By inverting data from more than ten years of continuous seismicity monitoring, we retrieved time-constant velocity anomalies, whose shapes correlate well with crustal lithology, while time-changing (up to 20%) velocity anomalies are mapped in the central region. Here, the Vp-to-Vs changes at depths of 1–5 km and 8–12 km correlate well with groundwater recharge and geodetic displacement during the same time interval. This correlation provides evidence for the existence of pulsating, pore pressure changes induced by groundwater recharge processes in a deep volume (8–12 km of depth), fractured and saturated with a predominant gas phase (likely CO2). We suggest that tomographic measurements of the Vp-to-Vs spatiotemporal changes are a suitable proxy to track the pore pressure evolution at depth in highly sensitive regions of fault systems.

Contributions from lithospheric and upper-mantle heterogeneities to upper crustal seismicity in the Korean Peninsula

SUMMARY The Korean Peninsula (KP), located along the eastern margin of the Eurasian and Amurian plates, has experienced continual earthquakes from small to moderate magnitudes. Various models to explain these earthquakes have been proposed, but the origins of the stress responsible for this region's seismicity remain unclear and debated. This study aims to understand the stress field of this region in terms of the contributions from crustal and upper-mantle heterogeneities imaged via seismic tomography using a series of numerical simulations. A crustal seismic velocity model can determine the crustal thickness and density. Upper-mantle seismic velocity anomalies from a regional tomography model were converted to a temperature field, which can determine the structures (e.g. lithospheric thickness, subducting slabs, their gaps, and stagnant features) and density. The heterogeneities in the crustal and upper mantle governed the buoyancy forces and rheology in our models. The modelled surface topography, mantle flow stress, and orientation of maximum horizontal stress, derived from the variations in the crustal thickness, suggest that model with the lithospheric and upper-mantle heterogeneities is required to improve these modelled quantities. The model with upper-mantle thermal anomalies and east–west compression of approximately 50 MPa developed a stress field consistent with the observed seismicity in the KP. However, the modelled and observed orientations of the maximum horizontal stress agree in the western KP but they are inconsistent in the eastern KP. Our analysis, based on the modelled quantities, suggested that compressional stress and mantle heterogeneities may mainly control the seismicity in the western area. In contrast, we found a clear correlation of the relatively thin lithosphere and strong upper-mantle upwelling with the observed seismicity in the Eastern KP, but it is unclear whether stress, driven by these heterogeneities, directly affects the seismicity of the upper crust.

Controls on Seasonal Variations of Crustal Seismic Velocity in Taiwan Using Single‐Station Cross‐Component Analysis of Ambient Noise Interferometry

AbstractAmbient noise interferometry is a powerful technique to continuously measuring crustal seismic velocity changes (dv/v) and studying crustal behaviors over time. However, the interpretation of such dv/v variations is not straightforward since multiple causes including internal (tectonic/magmatic) processes of the crust and external (environmental) factors could both affect dv/v simultaneously. To differentiate the interplay between the internal and external processes in dv/v variations is an essential step toward accurate crustal monitoring. In this study, we apply the single‐station cross‐component (SC) method to 15 selected stations from the Broadband Array in Taiwan for Seismology (BATS) to investigate the temporal evolution of crustal seismic velocities across Taiwan. We process the continuous BATS seismic recording from 1998 to 2019, construct the daily SC correlation functions, and compute dv/v values by the stretching technique in a frequency band of 0.1–0.9 Hz. We observe both strong annual dv/v variations and co‐seismic velocity drops associated with regional moderate‐to‐large earthquakes. Systematic spectral and time‐series analyses with the weather data suggest that the rainfall‐induced pore‐pressure change plays a predominant role in driving the dv/v seasonality, reflecting a diffusion process from meteoric water into shallow crust. The effects of other factors are relatively local and secondary. We also demonstrate how understanding and correcting rainfall effects could critically improve the resolution and accuracy of internal crustal damage related to earthquakes.

Hydrothermal Models Constrained by Fine‐Scale Seismic Velocities Confirm Hydrothermal Cooling of 7–63 Ma South Atlantic Crust

AbstractAlthough 70% of the Earth's heat loss occurs in the oceans, the nature of hydrothermal heat flow in oceanic crust is controversial. Lithospheric cooling models, heat flow measurements, and seismic experiments provide conflicting accounts on the longevity of hydrothermal systems and their efficiency at removing heat from the crust. Here we present five hydrothermal models along a crustal flowline in the western South Atlantic at ∼31°S to quantify how conductive and advective heat loss change as a function of crustal age and structure. The model sites cover crustal ages of 7–63 Ma and are collocated with planned drill sites of International Ocean Discovery Program Expeditions 390 and 393. We constrained our hydrothermal models with detailed physical property distributions that we estimated from new high‐resolution seismic velocity models. The hydrothermal models yield conductive and advective heat fluxes that closely match lithospheric cooling models and conductive heat flow measurements on the seafloor, supporting a hydrothermal sealing age of ∼65 Ma. Our results also agree with global estimates of fluid volume flux into the oceans and are consistent with a previously published analysis of upper crustal seismic velocities in the study area, indicating ongoing hydrothermal activity at relatively old crustal ages. This study broadly confirms and unifies existing concepts of oceanic heat flow and its modes of transport. Moreover, it provides a regional framework of seismic velocities and modeled hydrothermal fluxes, in which future in‐situ measurements can be integrated.

The crustal structure of the Kerimbas Basin across the offshore branch of the East African Rift System

SUMMARY The Davie Fracture Zone (DFZ) evolved during the Jurassic and Cretaceous breakup and subsequent drift of Gondwana off East Africa. This old weak zone has been reactivated during the evolution of the East African Rift System. Recent faulting of Cenozoic sediments in the Kerimbas Basin off northern Mozambique shows that they are affected by the neotectonics. The question is if and how the crustal fabric in our research area has been modified by the rifting process. We present two seismic refraction profiles acquired offshore northern Mozambique to investigate its regional crustal structure and tectonic history. The profiles show a continent–ocean transition zone that widens from around 40 km at 13°S to more than 100 km at 11°S. In the west the transitional crust is up to 12 km thick. To the east, around 150 km off the Mozambique coast lies oceanic crust whose thickness varies from 4.9 to 6.5 km along the northern line and from 6.5 to 7.5 km along the southern one. The latter presents an unusual high-velocity lower crustal body (7.0–7.2 km s−1), about 40 km wide and 3.8 km thick, underlying the oceanic crust. The body may consist of underplated melt with the same source as the nearby Paisley Seamount, which has not yet reached its isostatic equilibrium. Despite well documented recent seismicity along the margin, neither of the profiles reveal significant crustal modifications or reduced crustal seismic velocities that might be related to ongoing extensional tectonics as part of of the East African Rift System. Neither profile reveals seismic evidence for the presence of a major fracture zone or sheared continental margin parallel to the margin. Instead, the profiles’ broad continent–ocean transitions are consistent with their formation during an early Jurassic stage of plate divergence oblique to the margin. Later, after 157 Ma, the azimuth of relative plate motion between East and West Gondwana changed to be parallel to the margin, and parts of the continent–ocean transitions may have been locally reactivated in a strike-slip sense. However, details on the plate movements during the directional change of the seafloor spreading between 157 and 144 Ma are not available. The oceanic crust formed by the initial divergent oblique extension became faulted/modified by the strike-slip movements between both plates. Instead of a narrow deformation zone, the DFZ is charcaterized by a broad, diffuse zone of transtensional deformation.

Crustal attenuation beneath western North America: Implications for slab subduction, terrane accretion and arc magmatism of the Cascades

The western margin of the North American continent is a composite of diverse crustal domains featuring ancestral cratons, the Cordilleran terranes and the subducting Cascadia slab. Their existence and spatial extent have been largely inferred from seismic imaging, which is highly sensitive to variations in both crustal seismic velocity and attenuation structures. In this study, we improve upon existing, yet relatively limited, knowledge of crustal attenuation by developing a new Lg-wave attenuation (Q0) model. Benefiting from a comprehensive data set from dense seismic networks in Canada and the United States, our model reveals a clear transition from the low-attenuation (Q0>450) Canadian Shield to the highly-attenuated (Q0<150) crust near the Cascade arc. In the former region, the low-attenuation structures agree well with the distribution of thick, high-velocity crust in the Cordilleran foreland, suggesting dominant effects of elastic properties such as scattering and geometry of the crustal waveguide on the attenuation characteristics of stable cratons. On the other hand, we observe strong crustal attenuations in magmatically active areas including the Cascade arc and the Yellowstone-Snake River Plain volcanic province. The excellent spatial correlation between the high-attenuation Cascades and the surface projection of the subducting slabs further suggests a possible role of slab dehydration in increasing the fluid content of the overlying continental crust and modifying seismic attenuation. The sharp termination of the highly-attenuated crust forms a structural boundary in the Cascade back-arc that likely marks the eastern subsurface limit of the Siletzia terrane. The close spatial affinity of this boundary to the isotopic ratio lineament of 87Sr/86Sr = 0.706, which is the suggested ancestral continental margin, highlights the distinctive crustal types and/or heterogeneous structures between young accreted terranes and ancient cratons.

3-D travel-time tomography of southernmost Baja California Peninsula

A three-dimensional P and S-wave travel-time tomography, as well as Vp/Vs ratio images, were obtained for the southernmost tip of the Baja California Peninsula in Mexico. The area analyzed include Los Cabos block and part of the Gulf coast. The tomography obtained reveals in detail the heterogeneities of the crustal seismic velocity structure of the Los Cabos block. Results show an overall low velocity structure for both P- and S-waves under the Baja California peninsula down to a depth of ~25 km around the peninsular axis, particularly under Sierra La Laguna and near the Gulf of California (GoC) coast. Low P- and S-wave velocities are also present under the Gulf near the coast whereas fast velocities are observed under the Gulf away from the shoreline. Low and high Vp/Vs ratios are observed to alternate throughout the study area. The low seismic velocities may be explained because the crust in Los Cabos block is highly fractured and fluid-saturated, and has a high heat flux which is manifested as geothermal activity (e.g. hot springs observed all along the block). These low body wave velocities coincide with the existence of an asthenospheric mantle sandwiched by the continental crust of the Los Cabos block and a stalled subducted slab reported by Di Luccio et al. (2014). This mantle strip may be chemically depleted or dry inhibiting the development of active post-subduction volcanism.

Crustal body–wave velocities beneath Thailand from teleseismic analysis

We estimated the crustal seismic body-wave velocities beneath Thailand and Malay Peninsula by using teleseismic waveform analysis from 7 earthquakes in Prachuap Khiri Khan, Thailand. The seismic waveform studies on phase arrivals of P–wave and S-wave data retrieve from 2 broadband seismic stations, 1 CHTO station (Chiang Mai–Thailand) and 2 BTDF station (Singapore), are analysed in this paper. Obviously, the crustal seismic velocities from each stations were difference, with Vp (7.683–7.892 km/s) and Vs (4.275–4.403 km/s) propagations in the southern path (Malay Peninsula) are greater than Vp (7.556–7.827 km/s) and Vs (4.220–4.376 km/s) propagates in the northern path. The results show that to the corresponding with differ in earth’s crust density, the continental crust is less dense than the oceanic crust, and these data available for crustal seismic velocity for these region.

Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland's Northern Volcanic Zone.

Seismic noise interferometry is an exciting technique for studying volcanoes, providing a continuous measurement of seismic velocity changes (dv/v), which are sensitive to magmatic processes that affect the surrounding crust. However, understanding the exact mechanisms causing changes in dv/v is often difficult. We present dv/v measurements over 10 years in central Iceland, measured using single-station cross-component correlation functions from 51 instruments across a range of frequency bands. We observe a linear correlation between changes in dv/v and volumetric strain at stations in regions of both compression and dilatation associated with the 2014 Bárðarbunga-Holuhraun dike intrusion. Furthermore, a clear seasonal cycle in dv/v is modeled as resulting from elastic and poroelastic responses to changing snow thickness, atmospheric pressure, and groundwater level. This study comprehensively explains variations in dv/v arising from diverse crustal stresses and highlights the importance of deformation modeling when interpreting dv/v, with implications for volcano and environmental monitoring worldwide.