Wave Receiver Functions Research Articles

Imaging the Upper 10 km Crustal Shear-Wave Velocity Structure of Central Myanmar via a Joint Inversion of P-Wave Polarizations and Receiver Functions

Abstract Myanmar occupies a complex region in the active Indo-Burma subduction system. To illuminate the upper 10 km crustal structure of central Myanmar and obtain new insight into the subduction system, we jointly use P-wave polarizations and receiver functions (RFs) to construct a high-resolution VS profile based on a Bayesian Markov chain Monte Carlo approach. This obtained profile clearly delineates six tectonic units and their boundaries, including the Indo-Burman ranges (IBR), the IBR-fore-arc basin boundary, the fore-arc basin, the volcanic arc, the back-arc basin, and the Sunda plate. The Sunda plate has relatively higher upper crustal VS (>3.0 km/s) and thinner sedimentary cover (∼1 km) compared with the Central Myanmar basin in the Burma plate. The fore-arc basin, containing thick sediments (>10 km), and the back-arc basin, with thinner sediments (∼1–6 km), are separated by a region with higher VS (∼3.0 km/s), which represents crystallized magma beneath the volcanic arc. A narrow zone of relatively high-VS (∼2.6–2.7 km/s) ophiolites is situated between the fore-arc basin and the IBR. We also find a narrow zone of high-VS (∼2.9 km/s) metamorphic rocks contained within the low-VS (≲2.3 km/s) IBR. This study suggests that the proposing joint inversion of two types of single-station measurements, that is, P-wave polarizations and RFs, can robustly and computationally efficiently image the shallow VS structure and provide a reliable uncertainty estimation.

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Joint inversion of body wave arrival times, surface wave dispersion data and receiver functions: Method and Application to south China

Lithospheric structure beneath the Qinling Orogenic Belt and its surrounding regions: Implications for regional lithosphere deformation

AbstractWe present a lithospheric shear‐wave velocity model for the Qinling Orogenic Belt (QOB) and its surrounding regions through joint inversion of surface wave dispersion and receiver functions. Our model reveals large‐scale extremely low‐velocity zones (Vs ≤ 3.4 km/s) beneath the Northeastern Tibetan Plateau without further eastward extension, implying the absence ductile crustal flow beneath the eastern part of QOB. Pronounced upper‐mantle low‐velocity anomalies are imaged beneath the North Qinling and Weihe basin, suggesting the existence of deep mantle upwellings that lead to the extensional tectonics in these regions. A high‐velocity zone running continuously from the Alxa block to the eastern part of Qilian orogen in the uppermost mantle is revealed. We identify the high‐velocity zone to be the Asian mantle lithosphere and infer the development of southward underthrusting towards Qilian orogen.

X‐Discontinuity Beneath the Indian Shield—Evidence for Remnant Tethyan Oceanic Lithosphere in the Mantle

AbstractBeneath the continents and island arcs, a seismic discontinuity is often detected around 300 km depth, referred to as the X‐discontinuity. Various mineralogical and petrological mechanisms have been put forth to explain its occurrence. Because of the large depth variability, it is challenging to explain its origin invoking a single mineralogical phase transition. In order to investigate this discontinuity beneath India, we analyzed 10,216 P wave receiver functions at seismological stations deployed on the Indian shield and the Himalayas. We detect the X‐discontinuity as a sporadic and thin feature, in the depth range of 246–335 km, with a sharp shear velocity jump of 2.5%–3.6%. It neither bears a clear tectonic affinity nor has any correlation with the transition zone discontinuities. Interpreting its origin due to a single mineralogical change warrants a large spatial variation in the mantle temperature. Therefore, we suggest that the observed widespread X‐discontinuity beneath the Indian shield owes its origin to two mechanisms, that is, Orthoenstatite to high pressure Clinoenstatite transformation which shifts to lower pressures (∼2 GPa) due to the presence of water (0.13 wt% H2O) in MgSiO3 and coesite‐stishovite transition occurring at 8–11 GPa due to excess silica in an eclogitic component derived from the Tethys oceanic lithosphere subducted during lower Eocene. The identification of such a discontinuity could allow tracking of subducted material within the upper mantle providing a measure of mantle geochemical heterogeneity.

The Crustal Anisotropy of West Ordos Block and Its Geodynamic Implications

AbstractBased on the teleseismic records of the dense broadband seismic array, the crustal anisotropy parameters of the west Ordos block and its adjacent regions were determined with P wave receiver functions. The results indicate that the dominant direction of the fast wave is NEE‐SWW, N‐S in Yingshan block and north Ordos block, N‐S in the south Ordos block, and E‐W in the Qinling–Dabie orogen belt. The fast wave direction of crustal anisotropy in the north Ordos block is distinctly different from that in the south Ordos block, both well related to the major geological events, such as the Paleoproterozoic continent‐to‐continent collision between the Ordos Block and the Yinshan Block, the collision between the Western Block and Eastern Block of the North China Craton and the material migration from the Tibetan plateau in Cenozoic. Our results indicate that the crustal anisotropy in the Ordos block preserves the traces of ancient tectonic movements. Combining the results of previous geophysical studies, we presented a crust‐mantle interaction model to explain the geophysical observations. The most prominent features of the model are the horizontal eastward expansion of the mantle material in the southern Ordos and the vertical upwelling of the mantle material in the northern Ordos. The different modes of movement of the mantle material led to the deep contrasting structures of north and south Ordos, including the crustal anisotropy. The mantle upwelling also implies that the north Ordos block might be currently experiencing craton destruction.

High‐Resolution Crustal and Uppermost Mantle Structure Beneath Central Mongolia From Rayleigh Waves and Receiver Functions

AbstractIn this study, I present a high‐resolution 3‐D Vs model of the crust and uppermost mantle beneath central Mongolia, based on seismic data recorded at the Central Mongolia Seismic Experiment array and some other networks. The model is constructed by a Bayesian Monte Carlo inversion that jointly interprets Rayleigh wave phase speeds and receiver functions. The Rayleigh wave dispersion measurements are derived from both ambient noise and teleseismic earthquake data. To improve ambient noise data coverage, a recently developed three‐station interferometry (Zhang et al., 2020, https://doi.org/10.1093/gji/ggaa046) technique is applied to produce high‐quality three‐station interferograms that augment the ambient noise data base. There are several prominent geological and tectonic features captured by the model, including (1) the Khövsgöl rift system is imaged as a high‐speed anomaly in the upper crust, whose southern edge follows the Bulnay fault. (2) The estimated crustal thickness map identifies relatively thick crust beneath the Khövsgöl rift system, the Hangay Dome, and the Gobi‐Altai Mountains. (3) A crustal high‐velocity anomaly is imaged beneath the Taryatu‐Chulutu volcanic field, which is interpreted as a solidified intrusive magma body. (4) Dispersed low‐velocity anomalies in the mantle identify locations with possible partial melting. The melting zones could be related to small‐scale asthenospheric upwelling and convective removal of lithosphere, which produces uplift of the Hangay Dome.

Lithospheric structures beneath the western Mongolian Plateau: Insight from S wave receiver function

• S wave receiver functions reveals lithospheric structures in western Mongolia. • Two velocity discontinuities (i.e., LAB and MLD) are notable in the upper mantle . • Lower part of the lithosphere beneath the Hangay Dome has been delaminated. The Mongolian Plateau is located in the western segment of the Central Asian Orogenic Belt. In the Cenozoic, the western plateau was affected by the India-Asian collision; the Hangay Dome of a low-relief plateau has been formed. However, the mechanism of the uplift of the plateau and particularly the Hangay Dome is debated. In this study, we image the lithosphere-asthenosphere boundary (LAB) with S wave receiver functions. The LAB is much shallower beneath the western Mongolian Plateau (~80–90 km) than beneath the North China Craton (~150 km) and Siberian Craton (~180 km). We also found another possible deep LAB at 200–250 km depths beneath the Hangay Dome, indicating a lithospheric delamination beneath western Mongolia. Thus we conclude that the consequential asthenospheric upwelling caused the tectonic uplift of the Hangay Dome.

Seismic Imaging of the Subducted Australian Continental Margin Beneath Timor and the Banda Arc Collision Zone

AbstractDetailed crustal and uppermost mantle structure is imaged for the first time utilizing ∼4 years of broadband seismic data newly collected in the Timor‐Leste and Nusa Tenggara Timor region of Indonesia. We apply three techniques, ambient noise tomography, teleseismic P wave receiver function, and coda autocorrelation, to resolve a 3D Vs model and Moho structure. Our tomographic images show low‐velocity anomalies (<30 km) beneath Timor related to underthrusted Gondwana sequence from the Australian plate, which are vertically offset by the high‐velocity backstop of the Banda forearc terrane. The structure progressively changes along strike, reflecting different collisional stages developed as a result of the oblique convergence. At greater depth, we detect seismically fast lithospheric mantle (>30 km) and the arc‐ward dipping Moho beneath Timor, both interpreted to be from the Australian plate. Our findings provide direct structural evidence of the Australian continental margin at lithospheric depths beneath the Banda Arc collisional zone.

Global receiver function observations of the X-discontinuity reveal recycled basalt beneath hotspots

The distribution of chemical heterogeneity beneath hotspots provides important constraints on the source of magmatism and mantle convection. Chemical heterogeneities in the upper mantle produce discontinuities that can be interrogated seismically. One such discontinuity, the X-discontinuity (230-350 km depth), is observed intermittently across the globe, with multiple possible causal mechanisms. However, to better understand the cause of the X-discontinuity and its relationship to mantle upwellings, we require global short wavelength observations, previously unresolved by reflected phases with broad upper mantle Fresnel zones. Discontinuities resulting from seismically observable impedance contrasts can be targeted using high frequency P wave receiver functions (RFs) possessing short wavelength lateral sensitivity (∼100 km) to structures almost directly beneath the station. Thus, below well-instrumented hotspots we can investigate the properties of the X-discontinuity and constrain the causal mechanisms in these locations.Using P-to-s converted teleseismic phases between 30-90∘, we stack RFs in the depth and time-slowness domains at 28 hotspots and 6 cratons globally. This reveals 15 robust X-discontinuity observations beneath hotspots between 244-344 km depth. A further 10 potential observations are present beneath hotspots, and 6 null observations beneath cratons. Two causal mechanisms remain possible at the elevated mantle temperatures expected beneath hotspots. The coesite-stishovite phase transition occurs in eclogite and/or carbonated silicate melt may form under certain conditions. For either mechanism to provide seismically observable impedance contrasts, the upper mantle must be locally enriched in basalt. Assessing the X-discontinuity global distribution reveals a correlation with the Large Low Velocity Provinces, suggesting that mantle plumes may entrain recycled basalt from the lowermost mantle.

Hales Discontinuity in the Southern Indian Continental Lithosphere: Seismological and Petrological Models

AbstractWe model the depth and Vs structure of the Hales discontinuity (H‐D) beneath Eastern Dharwar Craton (EDC) and Southern Granulite Terrain (SGT) using P wave receiver function (P‐RF) analysis and joint inversion with Rayleigh wave phase velocity dispersion. We calculate P‐RFs at higher frequency (fmax = 0.46 Hz), compared to previous studies, to show that the H‐D P‐to‐S converted phase (Phs) is distinct from crustal reverberations. Phs at stations Hyderabad (HYB) and Gauribidanur (GBA), in the EDC, arrive at ∼11.5 s and ∼12 s, respectively. From joint inversion, the H‐D is modeled at 107 ± 5 km and 113 ± 4 km depth, with ∼3% and ∼4% Vs increase, beneath HYB and GBA, respectively. For station Kodaikanal (KOD), in SGT, the Phs destructively interferes with the negative midcrustal reverberation at most ray‐parameters, which explains its apparent absence in previous studies. We isolated P‐RFs where Phs is distinct at ∼11 s and model it at 102 ± 3 km depth. Common conversion point stack profiles constructed by depth migrating P‐RFs through the Vs model show an undulatory nature of the H‐D. From data of mantle xenoliths (Wajrakarur kimberlite field), we calculate Vs of mantle peridotite and eclogite, using published bulk rock compositions. At the H‐D depth and temperature derived from Indian shield geotherm, we observed a good match to the Vs structure of the H‐D. Our results support the geodynamic model of the H‐D being an interface of paleosubducted eclogitic oceanic crust embedded within the upper mantle peridotite. Global observations of mantle reflectors within the continental lithosphere, at depths similar to H‐D, have been related to relict subduction and independently support our model.

Shallow seismic structure beneath the continental China revealed byP-wave polarization, Rayleigh wave ellipticity and receiver function

SUMMARYWe construct a high-resolution shallow 3-D seismic model in the top 10 km of the upper crust in the continental China, with constraints of P polarization, Rayleigh wave ellipticity and receiver function obtained from records of 3848 seismic stations. Our 3-D seismic model has a spatial resolution of 0.6–1.2° in the north–south seismic belt and the trans-north China orogen, and 1–2° in the rest of the continental China (except the Tarim basin and the southwest Tibet). The seismic model exhibits low velocity anomalies of deposits in major sedimentary basins and high velocity anomalies of crustal bedrocks in young orogenic belts and old tectonic blocks. The inferred sediment thickness maps display thick deposits in major sedimentary basins, some compacted sediments in the intermontane basins in young orogenic belts and little sediments in old tectonic blocks. We also discuss compaction effects of the sediments and implications of tectonic history and geological evolution of the major basins in the continental China based on the inferred seismic models. This study provides an effective mean of seismic imaging through joint inversion of various seismic constraints and establishes a framework of seismic data sharing for future studies in the seismological community in a first step of developing a China Seismological Reference Model.

Shallow Shear-Wave Velocity Structure in Oklahoma Based on the Joint Inversion of Ambient Noise Dispersion and TeleseismicP-Wave Receiver Functions

ABSTRACTAmbient noise cross-correlations, used to obtain fundamental-mode Rayleigh-wave group velocity estimates, and teleseismic P-wave receiver functions are jointly modeled to obtain a 3D shear-wave velocity model for the crust and upper mantle of Oklahoma. Broadband data from 82 stations of EarthScope Transportable Array, the U.S. National Seismic Network, and the Oklahoma Geological Survey are used. The period range for surface-wave ambient noise Green’s functions is from 4.5 to 30.5 s constraining shear-wave velocity to a depth of 50 km. We also compute high-frequency receiver functions at these stations from 214 teleseismic earthquakes to constrain individual 1D velocity models inferred from the surface-wave tomography. Receiver functions reveal Ps conversions from the Moho, intracrustal interfaces, and shallow sedimentary basins. Shallow low-velocity zones in the model correlate with the large sedimentary basins of Oklahoma. The velocity model significantly improves the agreement of synthetic and observed seismograms from the 6 November 2011 Mw 5.7 Prague, Oklahoma earthquake suggesting that it can be used to improve earthquake location and moment tensor inversion of local and regional earthquakes.

Measuring PmP travel times using teleseismic S-wave waveform data*

Joint inversion for crustal velocity structure using only surface wave dispersion and receiver function data often suffers the non-unique solution problem due to lack of P wave velocity constraint in the data. Here we developed a method for measuring PmP travel time using teleseismic S wave waveform. The major improvement by this method over the previous one-layer-crust search method is its use of a more realistic multi-layer-crust (MLC) velocity model in the study region based on available information. Numerical tests show that compared with the previous search method the MLC search method is faster and more reliable and accurate. One limit of the MLC search method is the requirement of a multi-layer background model, thus this method might not be applicable in regions where the velocity structure is unknown. Nevertheless, our numerical tests show that the MLC search method is robust in the sense that small deviations of the background model from the true velocity model do not influence the results severely. We applied the MLC search method to data from a temporary linear array across the Wabash Valley Seismic Zone in the central USA. We obtained 157 PmP travel-time measurements that show lateral crustal structure variation in the region. The measurements provide additional constraints in joint inversion for crustal velocity structure in this seismically active region.

Location and characteristics of the X-discontinuity beneath SW Morocco and the adjacent shelf area usingP-wave receiver functions

SUMMARYReceiver function approaches have proven to be valuable for the investigation of crustal and upper mantle discontinuities whose sharp changes in seismic velocities cause wave conversions. While the crustal and mantle transition zone discontinuities are largely understood, the X-discontinuity at 250–350 km depth is still an object of controversial debate. The origin and global distribution of this structure with a velocity jump of 1.5–4.8 % for compressional and shear waves is still unexplained. Although the crustal and mantle transition zone discontinuities beneath SW Morocco and surroundings have been investigated, only a few studies observed the X-discontinuity and place the depth at 260–370 km beneath the region of western Morocco. In order to better locate and characterize the X-discontinuity beneath southwest Morocco, we create P-wave receiver functions using data recorded by the Morocco–Münster array and detect the X-discontinuity at apparent depths of 285–350 km. In the western part of our study region we find apparent depths of ∼ 310–340 km. The eastern part of the study area appears more complex: we locate two velocity jumps at apparent depths of around 285–295 km and 330–350 km in the northeast, and in the southeast we find a discontinuity at apparent depths of 340–350 km. Due to the large depth range and the twofold appearance of the X-discontinuity, we suggest that two different phase transitions cause the X-discontinuity beneath SW Morocco. The velocity contrasts at larger depths likely point to the coesite–stishovite phase transition occurring in deep eclogitic pools. The shallower depths can be explained by the transition from orthoenstatite to high-pressure clinoenstatite which requires the reaction between eclogite and peridotite to form orthopyroxene-rich peridotite. This reaction is likely related to previously proposed small-scale mantle upwellings beneath SW Morocco. Since both phase transitions require eclogite occurrence, the location of the X-discontinuity in this region can be used to indicate the location of recycled oceanic crust.

Receiver Function Velocity Analysis Technique and Its Application to Remove Multiples

AbstractResults of P wave receiver function (RF) analysis (e.g., H‐κ stacking, common conversion point (CCP) stacking, and migration) depend on the velocity models employed. Converted phases of crustal and upper mantle discontinuities are often interfered by multiple reflections from shallower structures, adding further complexity to the interpretation of P wave RF images. In this study, we propose a receiver function velocity analysis technique (RFVAT) that can constrain the velocity structure above discontinuities and remove multiple reflections arising from target discontinuities. By scanning the amplitude spectra of the Ps and PpPs phases, we can obtain precise arrival times of these phases for interfaces above 250 km (errors < 0.13 s) and derive the average velocities and thicknesses of the layers between interfaces in the crust and upper mantle. Synthetic experiments are used to demonstrate that crustal and upper mantle discontinuities can be coherently identified and that multiple reflections can be effectively removed in the CCP stacking images of P wave RFs using the RFVAT even with low signal‐to‐noise ratio data. By applying the proposed RFVAT to real P wave RF data from the northeastern part of the North China Craton, we achieve an improvement in CCP stacking image of lithospheric discontinuities, especially for the lithosphere‐asthenosphere boundary (LAB). Our P wave RF images reveal distinct lateral variations of the LAB depth. The lithospheric thickness extends to ~120 km beneath the central orogenic belt and decreases sharply to ~80 km at the west edge of the eastern block, consistent with previous S wave RF studies.

Crustal Structure of Sri Lanka Derived From Joint Inversion of Surface Wave Dispersion and Receiver Functions Using a Bayesian Approach

AbstractWe study the crustal structure of Sri Lanka by analyzing data from a temporary seismic network deployed in 2016–2017 to shed light on the amalgamation process from a geophysical perspective. Rayleigh wave phase dispersion curves from ambient noise cross correlation and receiver functions were jointly inverted using a transdimensional Bayesian approach. The Moho depths in Sri Lanka range between 30 and 40 km, with the thickest crust (38–40 km) beneath the central Highland Complex (HC). The thinnest crust (30–35 km) is found along the west coast, which experienced crustal thinning associated with the formation of the Mannar Basin. VP/VS ratios lie within a range of 1.60–1.82 and predominantly favor a felsic to intermediate bulk crustal composition with a significant silica content of the rocks. A major intracrustal (18–27 km), slightly westward dipping (∼4.3°) interface with high VS (∼4 km/s) underneath is prominent in the central HC, continuing into the western Vijayan Complex (VC). The discontinuity might have been part of the respective units prior to the collision and could be an indicator for the proposed tilting of the Wanni Complex/HC crustal sections. It might also be related to the deep crustal HC/VC thrust contact with the VC as an indenting promontory of high VS. A low‐velocity zone in the central HC could have been caused by fluid influx generated by the thrusting process.

LitMod2D_2.0: An Improved Integrated Geophysical‐Petrological Modeling Tool for the Physical Interpretation of Upper Mantle Anomalies

AbstractLitMod2D integrates geophysical and petrological data sets to produce the thermal, density, and seismic velocity structure of the lithosphere and upper mantle. We present a new LitMod2D_2.0 package with improvements focused on (i) updated anelastic attenuation correction for anharmonic seismic velocities, (ii) chemical composition in the sublithospheric mantle, and (iii) incorporation of sublithospheric mantle anomalies. Sublithospheric mantle anomalies can be defined with different chemical composition, temperature, seismic velocities, and a combination of them, allowing the application of LitMod2D_2.0 to regions affected by mantle upwelling, subduction, delamination, and metasomatism. We demonstrate the potential application of LitMod2D_2.0 to such regions and the sensitivity of thermal and compositional anomalies on density and seismic velocities through synthetic models. Results show nonlinearity between the sign of thermal and seismic velocity anomalies, and that S wave velocities are more sensitive to temperature whereas P wave velocities are to composition. In a synthetic example of subduction, we show the sensitivity of sublithospheric mantle anomalies associated with the slab and the corner flow on surface observables (elevation, geoid height, and gravity anomalies). A new open‐source graphic user interface is incorporated in the new package. The output of the code is simplified by writing only the relevant physical parameters (temperature, pressure, material type, density, and seismic velocities) to allow the user using predefined post‐processing codes from a toolbox (flexure, mineral assemblages, synthetic passive seismological data, and tomography) or designing new ones. We demonstrate a post‐processing example calculating synthetic seismic tomography, Rayleigh surface‐wave dispersion curves, and P wave receiver functions from the output file of LitMod2D_2.0.

Lake Van (Southeastern Turkey) Experiment: Receiver Function Analyses of Lithospheric Structure from Teleseismic Observations

The P and S wave receiver functions and their joint inversions are used to study the lithosphere beneath the Lake Van region using approximately 600 teleseismic earthquake data (Mw ≥ 5.8) at different azimuths collected from 10 permanent broadband stations operated by Kandilli Observatory and Earthquake Research Institute and Disaster and Emergency Management Authority in the region. The dataset is taken from the European Integrated Data Archive. The simulated annealing method is used for the joint inversion of P-wave and S-wave receiver functions, since the P410s phase cannot be detected reliably in the depth stacks. This may be due to the low olivine content and high basalt content at this depth. The inversion process is therefore performed without travel time residuals. The crustal thickness is observed at nearly 45 km in all the velocity models obtained from the inversion. The relatively low-velocity layer (Vs = 3.4 km/s) at depths of the middle crust may be associated with volcanic centers near Nemrut, in the west of the region. Additionally, another low-velocity layer (Vs = ~ 3.0 km/s) is observed in the upper crust around the Suphan Volcano. Also, Vp/Vs and Poisson’s ratios are calculated for the study area. Their high values (Vp/Vs ≥ 1.85, and σ ≥ 0.285) correspond to the partial melting of the lower crust in the region. According to velocity models obtained from the inversion results, the most important outcome is that the average variance of the Moho discontinuity (~ 45 km) and lithosphere–asthenosphere boundary (~ 90 km) under the seismograph stations can be interpreted as a likely part of the Arabian oceanic plate in relation to the collision zone.