Ps Conversions Research Articles

Deep low velocity layer in the sublithospheric mantle beneath India

SUMMARY Globally, there is now a growing evidence for a low velocity layer in the deeper parts of the upper mantle, above the 410 km discontinuity (hereafter called LVL-410). The origin of this layer is primarily attributed to interaction of slabs or plumes with a hydrous mantle transition zone (MTZ) that results in dehydration melting induced by water transport upward out of the MTZ. However, the ubiquitous nature of this layer and its causative remain contentious. In this study, we use high quality receiver functions (RFs) sampling diverse tectonic units of the Indian subcontinent to identify Ps conversions from the LVL-410. Bootstrap and differential slowness stacking of RFs migrated to depth using a 3-D velocity model reveal unequivocal presence of a deep low velocity layer at depths varying from 290 to 400 km. This layer appears more pervasive and deeper beneath the Himalaya, where detached subducted slabs in the MTZ have been previously reported. Interestingly, the layer is shallower in plume affected regions like the Deccan Volcanic Province and Southern Granulite Terrane. Even though a common explanation does not appear currently feasible, our observations reaffirm deep low velocity layers in the bottom part of the upper mantle and add to the list of regions that show strong presence of such layers above the 410 km discontinuity.

Evidence for weak azimuthal anisotropy beneath the Kumaon-Garhwal Himalaya

SUMMARY This study attempts to interrogate the upper mantle deformation pattern beneath the Kumaon-Garhwal region, located in the western Himalaya, using shear wave splitting (SWS) analysis of core-refracted (XK(K)S) phases recorded at 53 broad-band stations. The fast polarization azimuths (FPAs) revealed by 338 well constrained measurements are dominantly clustered around ENE–WSW, with a few along the NE and E–W directions. The delay times vary from 0.2 to 1.4 s, with an average of 0.6 s that is smaller than that for the Indian shield (∼0.8 s), central and eastern Himalayas. The northern part of the lesser Himalaya shows a slightly smaller delay time compared to the southern part, which is attributed to the weakening of azimuthal anisotropy caused by the dipping of the Indian lithosphere. In order to understand the crustal contribution, its anisotropy is measured by analysing the splitting of Ps conversions from the Moho (Pms), akin to that of the XK(K)S phases. However, reliable results for crustal anisotropy could be obtained only at 10 stations. The average delay time due to crustal anisotropy is 0.47 s, with a variation from 0.2 to 0.9 s. Although the dominant period of Pms is smaller than that of SK(K)S, crustal anisotropy contributing to splitting of the latter phases cannot be ruled out. The orientation of FPAs obtained from Pms phases is found to be parallel or sub-parallel to those from XK(K)S phases, suggesting a similar deformation mechanism in the mid- to lower-crust and upper mantle. On the basis of FPAs derived from XK(K)S measurements, the Kumaon-Garhwal Himalaya (KGH) region can be divided into four subregions. In the western and eastern parts, the FPAs are mostly aligned along NE and ENE–WSW, and NE, respectively. In the central and south-eastern parts, their orientation is along ENE–WSW and NW, respectively. The strong ENE–WSW orientation in the central part could result from a slightly variable anisotropy in the crust to the upper part of the lithosphere or basal topography causing deflection of mantle flow. Also, the NW orientation in the south-eastern part of KGH is associated with a shallow source within the lithosphere. Application of the spatial coherency technique to single-layered anisotropic parameters results in a depth of 220–240 km, implying that the dominant source of anisotropy could lie in the upper mantle.

On the detection of upper mantle discontinuities with radon-transformed receiver functions (CRISP-RF)

SUMMARYSeismic interrogation of the upper mantle from the base of the crust to the top of the mantle transition zone has revealed discontinuities that are variable in space, depth, lateral extent, amplitude and lack a unified explanation for their origin. Improved constraints on the detectability and properties of mantle discontinuities can be obtained with P-to-S receiver function (Ps-RF) where energy scatters from P to S as seismic waves propagate across discontinuities of interest. However, due to the interference of crustal multiples, uppermost mantle discontinuities are more commonly imaged with lower resolution S-to-P receiver function (Sp-RF). In this study, a new method called CRISP-RF (Clean Receiver-function Imaging using SParse Radon Filters) is proposed, which incorporates ideas from compressive sensing and model-based image reconstruction. The central idea involves applying a sparse Radon transform to effectively decompose the Ps-RF into its underlying wavefield contributions, that is direct conversions, multiples, and noise, based on the phase moveout and coherence. A masking filter is then designed and applied to create a multiple-free and denoised Ps-RF. We demonstrate, using synthetic experiment, that our implementation of the Radon transform using a sparsity-promoting regularization outperforms the conventional least-squares methods and can effectively isolate direct Ps conversions. We further apply the CRISP-RF workflow on real data, including single station data on cratons, common-conversion-point stack at continental margins and seismic data from ocean islands. The application of CRISP-RF to global data sets will advance our understanding of the enigmatic origins of the upper mantle discontinuities like the ubiquitous mid-lithospheric discontinuity and the elusive X-discontinuity.

Deep structure of the crust in the area of the 2016–2017 Central Italy seismic sequence from receiver function analysis

We compute a high-resolution topographic model of the Moho beneath the fault system activated during the 2016–2017 Central Italy seismic sequence, using Receiver Function (RF) analyses. We document that Ps conversions recorded in RF data-set varies abruptly at very short distance across the crustal lineament called Ancona-Anzio Line (AAL). Moho depth varies from about 25-30 km in the Tyrrhenian domain on the West to 35-40 km in the Adriatic domain in the East. Where the two domains are juxtaposed along the AAL, Moho depth values cluster around 50 km depth, in a stripe-like area 20 km wide. Such unique feature marks the deformation zone in the lithosphere and testifies the abrupt change in delamination style in the two sectors of the Apennines. Intermittent large normal faulting earthquakes driven by across-belt extension break through such inherited strong structural changes, conditioned by localized barriers to fluids migration and overpressuring.

The Signature and Elimination of Sediment Reverberations on Submarine Receiver Functions

AbstractWhile the receiver function technique has been successfully applied to high‐resolution imaging of sharp discontinuities within and across the lithosphere, it suffers from severe limitations when applied to seafloor seismic recordings. This is because the water and sediment layer could strongly influence the receiver function traces, making detection and interpretation of crust and mantle layering difficult. This effect is often referred to as the singing phenomena in marine environments. We demonstrate, using analytical and synthetic modeling, that this singing effect can be reversed using a selective dereverberation filter tuned to match the elastic property of each layer. We apply the dereverberation filter to high‐quality earthquake records collected from the NoMelt seismic array deployed on normal, mature Pacific seafloor. An appropriate filter designed using the elastic properties of the underlying sediments, obtained from prior studies, greatly improves the detection of Ps conversions from the Moho (∼8.6 km) and from a sharp discontinuity (<∼5 km) across the lithosphere asthenosphere transition (∼72 km). Sensitivity tests show that the dereverberation filter is mostly sensitive to the two‐way travel time of the shear wave in sediment and is robust to seismic noise and small errors in the sediment properties. Our analysis suggests that selectively filtering out the sediment reverberations from ocean seismic data could make inferences on subsurface structure more robust. We expect that this study will enable high‐resolution receiver function imaging of the oceanic plate across the growing ocean bottom seismic arrays being deployed in the global oceans.

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.

Moho Depth Variations From Receiver Function Imaging in the Northeastern North China Craton and Its Tectonic Implications

AbstractA detailed knowledge of the crustal thickness in the northeastern North China Craton (NCC) is important for understanding the unusual Phanerozoic destruction of the craton. We achieve this goal by employing a 2‐D wave equation‐based migration method to P receiver functions from 198 broadband seismic stations, using Ps conversions and surface‐reflected multiples. By combining receiver function images along 19 profiles, we constructed a high‐resolution Moho depth model for the northeastern NCC. The results present dominant E‐W Moho depth variations similar to previous observations and new regional N‐S variations beneath both sides of the North‐South Gravity Lineament. To the west, while a deeper Moho (∼42 km) appears in the interior of the Trans‐North China Orogen, a relatively shallow Moho (∼38 km) exists in the northern margin of the Trans‐North China Orogen to western NCC. To the east, the crust beneath the Yan Mountains in the marginal area is thicker (∼32–40 km) than that (∼26–32 km) beneath the Bohai Bay Basin in the craton interior, and the Moho further shallows from NE (∼32 km) to SW (∼26 km) within the basin. Along with other observations, we conclude that the dominant E‐W difference may have been associated with the Paleo‐Pacific plate subduction under eastern Asia since the Mesozoic. The newly observed complex N‐S variations may have reflected the structural heterogeneity of the cratonic lithosphere inherited since the formation of the NCC in the Paleoproterozoic, or spatially uneven effects on the cratonic lithosphere of subsequent thermotectonic events during the long‐term evolution of the craton, or both.

Structure of the Crust and Mantle Down to 700 km Depth beneath the Longmenshan From P Receiver Functions

AbstractSince the Ms 8.0 Wenchuan earthquake occurred in 2008 in the Longmenshan at the eastern margin of Tibet, this region has attracted much attention. In order to investigate the deep structure of the region, an analysis of P receiver functions was carried out, using data from an array of 80 broadband seismic stations operated in 2012 and 2013, and straddling the Longmenshan fault zone around the epicenter of the Wenchuan earthquake. Positive Ps conversions from 5 to 10 km depth indicate the base of the Mesozoic sediments in the Sichuan basin and the base of the Songpan‐Ganzi flysch deposits in Tibet. Later positive Ps conversions represent the Moho, which occurs at 40–50 km depth below the Sichuan basin and deepens to the NW to 55–70 km depth under Tibet. An important finding of this study is that whereas in the NE, the Moho deepening from SE to NW is smooth, in the middle and SW of the region the Moho deepening is abrupt with, in some places, a possible overlap. Negative Ps conversions at stations in Tibet represent the top of low shear velocity zones in the middle and lower crusts below Tibet. Beneath the Sichuan basin, a negative phase about 1 s earlier than the Moho Ps conversion is to a large extent, almost certainly due to multiples from discontinuities in the upper crust. Finally, positive Ps conversions can be observed from the 410 and 660‐km discontinuities at the top and bottom of the mantle transition zone, respectively.

Nature of the seismic lithosphere‐asthenosphere boundary within normal oceanic mantle from high‐resolution receiver functions

AbstractReceiver function observations in the oceanic upper mantle can test causal mechanisms for the depth, sharpness, and age dependence of the seismic wave speed decrease thought to mark the lithosphere‐asthenosphere boundary (LAB). We use a combination of frequency‐dependent harmonic decomposition of receiver functions and synthetic forward modeling to provide new seismological constraints on this “seismic LAB” from 17 ocean‐bottom stations and 2 borehole stations in the Philippine Sea and northwest Pacific Ocean. Underneath young oceanic crust, the seismic LAB depth follows the ∼1300 K isotherm but a lower isotherm (∼1000 K) is suggested in the Daito ridge, the Izu‐Bonin‐Mariana trench, and the northern Shikoku basin. Underneath old oceanic crust, the seismic LAB lies at a constant depth ∼70 km. The age dependence of the seismic LAB depth is consistent with either a transition to partial‐melt conditions or a subsolidus rheological change as the causative factor. The age dependence of interface sharpness provides critical information to distinguish these two models. Underneath young oceanic crust, the velocity gradient is gradational, while for old oceanic crust, a sharper velocity gradient is suggested by the receiver functions. This behavior is consistent with the prediction of the subsolidus model invoking anelastic relaxation mediated by temperature and water content, but is not readily explained by a partial‐melt model. The Ps conversions display negligible two‐lobed or four‐lobed back azimuth dependence in harmonic stacks, suggesting that a sharp change in azimuthal anisotropy with depth is not responsible for them. We conclude that these ocean‐bottom observations indicate a subsolidus elastically accommodated grain‐boundary sliding (EAGBS) model for the seismic LAB. Because EAGBS does not facilitate long‐term ductile deformation, the seismic LAB may not coincide with the conventional transition from lithosphere to asthenosphere corresponding to a change in the long‐term rheological properties.

Passive seismological imaging of the Narmada paleo-rift, central India

The Narmada-Son lineament (NSL) is a prominent, nearly E–W trending tectonic feature dividing India into the peninsular and extra-peninsular regions. It marks the possible suture between two contrasting geological settings termed proto-continents lying to the North and South of it. Various views prevail about the nature of the rift zone. The present study delineates the seismic structure of the crust using P wave receiver functions at 10 broadband seismic stations installed along a profile across the NSL. The results from Common Conversion Point (CCP) stacking reveal a near continuous image of the Moho boundary, with the amplitudes of the Ps conversions from the Moho being weaker at stations within the rift. Modelling the receiver functions employing nearest neighborhood algorithm approach brings out a distinct (15km) thickening of the crust and a complex nature of the Moho within the rifted zone. We find that the backazimuthal variations of the SV and SH receiver functions at the permanent station Jabalpur can be explained better by introducing azimuthal anisotropy in the middle and lower crust with the fast axes perpendicular to the rift axis. Also, we find substantial evidence of post rifting magmatic underplating in the lower crust, which could be reminiscence of Deccan volcanism and/or Reunion plume path.

Elastic P- and S-wave autofocus imaging with primaries and internal multiples

Conventional seismic imaging methods rely on the single-scattering Born approximation, requiring the removal of multiply scattered events from reflection data prior to imaging. Additionally, many methods use an acoustic approximation, representing the solid earth as an acoustic (fluid) medium. We have developed imaging methods for (solid) elastic media that use primaries and internal multiples, including their PS and SP conversions, thus obviating the need for internal multiple removal and improving handling of internal conversions. Our methods rely on the elastic autofocusing method, which estimates full multicomponent elastodynamic Green’s functions from virtual sources interior to the medium to receivers placed on the surface. They require only surface seismic reflection data and estimates of the direct waves from virtual sources interior to the medium, both of which are commonly available at the imaging step of seismic processing. We tested our methods on a synthetic model with constant P and S velocities and vertical and horizontal density variations, by producing, for the first time to our knowledge, PP and SS images from elastic autofocusing that are compared to reference seismic images based on conventional methods. The effects of multiples are greatly attenuated in the images, with fewer spurious reflectors than are observed when using Born imaging.

The influence of temperature, bulk composition, and melting on the seismic signature of the low-velocity layer above the transition zone

We report a new technique to describe seismic velocity and impedance anomalies atop a seismic low-velocity layer (LVL) at 350 km depth. We model shear wave speed reductions detected with Ps conversions beneath the Hawaiian Islands and negative impedance contrasts detected with ScS reverberations beneath the Coral Sea in the South Pacific, by varying the bulk solid composition, reference potential temperature, dihedral angle of melt, and melt composition. For a given bulk solid composition, the effects of elevated temperature and melt volume fraction on the seismic properties trade off with one another. At a given temperature, the calculated melt volume fraction is nearly insensitive to variations in the bulk solid composition. A low volume fraction of low dihedral angle melts mimics the seismic signature of a higher volume fraction of high dihedral angle melts. Despite stronger lateral variations in the LVL structure beneath Hawaii compared to the Coral Sea, both regional averages are similar. For a basalt volume fraction of 0.2 and a dihedral angle of 10°, we estimate regional averages of 1.1 ± 0.8 vol % melt at a depth of 350 km beneath the Hawaiian Islands for a reference potential temperature of 1800 K and 1.2 ± 0.005 vol % melt at a depth of 350 km beneath the Coral Sea region for a reference potential temperature of 1500 K. Our model of the seismic signal is unable to distinguish between melt compositions of mid-ocean ridge basalt and carbonated peridotite melts at such small melt volume fractions.

Estimating sedimentary and crustal structure using wavefield continuation: theory, techniques and applications

Receiver function techniques are widely used in imaging crustal and mantle structure beneath a seismic station. The weak P-to-S conversions at deep seismic structures are usually masked by strong shallow reverberations when unconsolidated sediments are present below the station, making it nearly impossible to utilize receiver function techniques. We develop a method to estimate sediment and crustal structures beneath a seismic station based on wavefield downward continuation and decomposition method. The method parametrizes velocity structure beneath the station with a stack of constant velocity layers overlying a homogeneous half-space, and approximates the teleseismic P wave and its coda by the structural response to an incoming plane P wave. Our method is based on the principle that the upgoing S wavefield is absent in the half-space, and searches for the optimum velocity and thickness of the layers that give the minimum S-wave energy flux from the half-space to the layers. An iterative grid-search algorithm from the top to the bottom layers is employed to implement the search. In this study, we only use models comprising either only one crust layer or two layers (sediment + crust) with a half-space mantle, although models with more layers are also implementable. The method is especially useful in resolving seismic structure beneath a station sitting on unconsolidated sediments. It not only can be used to determine the sediment thickness and velocity structure, but also provides an effective way to generate subsurface receiver functions, which are formed by deconvolving the upgoing P wavefield from the upgoing S waves at the top of hardrock crust, and thus are free from shallow reverberations. The technique is applied to various synthetic data generated with different types of velocity model and noise levels, and appears to have good capability in recovering the input models. We further applied this method to teleseismic data recorded at a station inside the Songliao Basin in northeast China. The estimated sediment thickness and velocity agrees well with the results of previous active-source studies. The subsurface receiver functions also show a superior power in exposing the Moho Ps conversions, resulting in a well-defined peak in the H-κ domain, which are absent in the regular receiver function data.

Mantle transition zone thickness beneath Cameroon: evidence for an upper mantle origin for the Cameroon Volcanic Line

SUMMARY The thickness of the mantle transition zone beneath Cameroon has been mapped using data from the 2005–2007 Cameroon Broadband Seismic Experiment to evaluate models for the originof the Cameroon Volcanic Line (CVL).Some 2200 receiver functions have been stacked using a 3-D velocity model, revealing Ps conversions from the mantle transition zone discontinuities at depths of ∼410 and 660 km. Results yield a nearly uniform transition zone thickness (251 ± 10 km) that is similar to the global average, implying that any thermal anomalies in the upper mantle beneath the CVL do not extend as deep as the transition zone. This finding, when combined with regional P and S velocity models of the mantle, supports an explanation attributing the origin of the CVL to upper mantle processes such as an edge flow convection cell in the upper mantle along the northwestern side of the Congo Craton lithosphere.

Converted wave seismic imaging in the Flin Flon mining camp, Canada

Abstract Seismic imaging for mineral exploration in hardrock environment has typically relied on P-waves recorded using vertical component geophones. Here we demonstrate the potential of using P-to-S converted waves for mineral exploration by applying converted wave processing to high-resolution 3-component data acquired in the Flin Flon mining camp, Canada. Inferences regarding the relative value of PS data are made through comparison with corresponding PP images, interpretation with geological constraints, and by comparison with modeling results. Modeling results show that the horizontal component data provide a robust means of separating the PS conversions from the PP reflections in converted wave processing whereas contamination by PP energy is more severe if the vertical component data are used. A customized processing workflow has been developed in which horizontal component data are sorted into common-reflection point gathers by the application of the converted wave dip-moveout operator. The PS images are characterized by lower signal-to-noise ratios than the PP images due to the smaller S-wave impedance contrasts associated with the main lithologic units and the angular dependence of P-to-S conversion. An exception to this occurs for PS reflections from the ore zones which are accentuated on the PS images relative to the background host-rock reflectivity. There are discrepancies in the reflection dips and positions observed on corresponding PP and PS sections that are not fully explained. They can be partly attributed to the non-coincidence of subsurface spatial sampling associated with common-depth points versus common-conversion points, with an additional complication associated with the known 3D geology. Vp/Vs ratios determined by correlation of reflections observed on PP and PS images can provide a limited means of lithological discrimination.

Wave-Field Continuation and Decomposition for Passive Seismic Imaging Under Deep Unconsolidated Sediments

Abstract The coastal plains of the central and eastern United States contain deep sections of unconsolidated to poorly consolidated sediments. These sediments mask deeper crustal and upper-mantle converted phases in teleseismic receiver functions through large amplitude, near-surface reverberations. Thick sediments also amplify ambient noise levels to generally reduce data signal-to-noise ratios. Removing shallow-sediment wave-propagation effects is critical for imaging deep lithospheric structures. A propagator matrix formalism is used to downward-continue the wave field for teleseismic P waves into the midcrust and then to separate the upgoing S -wave field from the total teleseismic response of the P wave to expose deep Sp conversions. This method requires that the Earth model from the surface to the reference depth be known. Teleseismic P -wave data for the Memphis, Tennessee, station (MPH) are analyzed using a reference-station deconvolution technique to produce vertical and radial P -wave transfer functions. These transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion. The inverted Earth model is incorporated into the wave-field continuation and decomposition technique to estimate the upgoing S -wave field at 10 km depth in the crust. Moho and possible deeper Ps conversions are identified with this process.

Crustal structure of Northwest Zagros (Kermanshah) and Central Iran (Yazd and Isfahan) using teleseismic Ps converted phases

Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset includes teleseismic data (M b ≥ 5.5, epicentral distance from 30° to 95°) recorded at 12 three-component short-period stations of Kermanshah, Isfahan and Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at the Moho boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ increases to 4.3 km/s beneath the Moho.

Mantle transition zone thickness beneath Ross Island, the Transantarctic Mountains, and East Antarctica

The thickness of the mantle transition zone beneath Ross Island, and parts of the Transantarctic Mountains and East Antarctic Craton has been mapped using data from the 2000–2003 Transantarctic Mountain Seismic Experiment to determine if, as indicated by some tomographic images, an upper mantle thermal anomaly centered beneath Ross Island is a deep‐seated feature extending into the mantle transition zone. Some 2700 receiver functions have been stacked using a 3D velocity model, revealing Ps conversions from the mantle transition zone discontinuities at depths of 410 and 660 km. Results yield an average nearly uniform transition zone thickness (266 ± 10 km) that is slightly larger than the global average, implying that the upper mantle thermal anomaly does not likely extend into the transition zone. This finding favors explanations for the upper mantle thermal anomaly invoking a plume head or small‐scale convection.

Simultaneous iterative time-domain sparse deconvolution to teleseismic receiver functions

SUMMARY In this paper, we present a new approach to estimate high-resolution teleseismic receiver functions using a simultaneous iterative time-domain sparse deconvolution. This technique improves the deconvolution by using reweighting strategies based on a Cauchy criterion. The resulting sparse receiver functions enhance the primary converted phases and its multiples. To test its functionality and reliability, we applied this approach to synthetic experiments and to seismic data recorded at station ABU, in Japan. Our results show Ps conversions at approximately 4.0 s after the primary P onset, which are consistent with other seismological studies in this area. We demonstrate that the sparse deconvolution is a simple, efficient technique in computing receiver functions with significantly greater resolution than conventional approaches.

Sedimentary and crustal structure beneath Kachchh and Saurashtra regions, Gujarat, India

Strong and distinct Ps conversions from Moho and top sediments characterize the radial receiver functions (RF) estimated for stations in Kachchh basin, while, these for stations in Saurashtra are characterized by a strong Ps conversion from Moho and a weak or absence of Ps conversion from top sediments. The jumping inversion of stacked radial RFs suggest that 1–3 km thick top low velocity sediments ( V p: 1.8–2.5 km/s; σ: 0.28–0.34) and a 39–48 km thick crust ( σ: 0.25) (thicker than average Precambrian crust) characterize the Kachchh basin area. While, the crust beneath Saurashtra is characterized by a 0–1 km thick moderate velocity sediments ( V p: 2.0–3.56 km/s; σ: 0.25–0.28) and a north dipping shallow Moho (35–42 km; σ: 0.248). The estimated average crustal σ values from the arrival times of PpPms and PpSms + PsPms phases suggest a relatively stronger crust in Kachchh ( σ: 0.22–0.27) in comparison to the crust in Saurashtra ( σ: 0.18–0.19). In the epicentral zone of 2001 Bhuj earthquake, the estimated Moho thickness reveals a Moho upwarping (3–5 km change in the E–W direction and a 6–9 km change in the N–S direction) beneath the epicentral zone of 2001 Bhuj earthquake, which might have induced large intraplate stresses to cause the M w 7.7 earthquake at 23 km depth.