Teleseismic Receiver Functions Research Articles

Lithospheric structure beneath southern Iberia and northern Morocco constrained by 3D Kirchhoff-approximate GRT imaging

AbstractThe slab beneath the Alboran Sea is a consequence of the collision between two continents (Europe and Africa), which was initiated along the northeastern Spanish coast, experienced slab rollback and migrated to the area adjacent to the two continents. The tectonic background in this area includes episodes of collisions with adjacent continents as well as extension of those basins in the western Mediterranean. Here, we present three-dimensional (3D) Kirchhoff-approximate generalized Radon transform (GRT) images to further constrain the lithospheric structures previously identified by other researchers. The GRT images were calculated from the same P-to-S (Pds or Ps) teleseismic receiver functions (RFs) as the previous common conversion point (CCP) stacking, but the GRT data provide figures with greater resolution than the Pds RFs CCP results. This study indicates that the Alboran Slab may have completely detached from the crustal base under the western Betics Mountains and that a larger range of lithospheric ‘peeling off’ developed beneath the western part of the Betics Mountains than some previous results have claimed. The observed thin lithosphere under the Middle Atlas (MA) and eastern High Atlas (HA) may have a geodynamic relationship with lithospheric delamination under the eastern part of the Rif Mountains, which has also led to the thin lithosphere under the eastern Rif. According to the thick lithosphere under the western HA, the shallow LAB under the MA and eastern HA may have no heat-flow connection with the Canary mantle plume, as stated in several previous studies.

Combining Petrology and Seismology to Unravel the Plumbing System of a Typical Arc Volcano: An Example From Marapi, West Sumatra, Indonesia

AbstractMarapi in Sumatra is characterized by frequent short‐lived explosions and small eruptions (Volcanic Explosivity Index 1–2) and in the past 250 years, the volcano has erupted >60 times. Recent volcanic bombs and the presence of broadband seismic stations lead us to reconstruct the plumbing system of the volcano through an interdisciplinary study. A petrologic study of the summit bombs uses pyroxene, plagioclase and glass compositions to obtain pressures and temperatures of magma storage as well as identify pre‐eruptive processes. Two‐pyroxene geothermobarometry provides pre‐eruptive crystallization pressure estimates of 4–7 kbar (∼15–26 km). Compositional and textural analyses of plagioclase and pyroxene crystals indicate that mafic magma recharge was followed by mixing with the resident magma and renewed crystallization prior to eruption. In order to further image the magma reservoir, we performed a joint inversion of teleseismic receiver functions and surface waves (H/V ratio). The inversion reveals a low velocity zone (LVZ) at depths of 15–21 km that has 7 ± 3% shear velocity reduction, corresponding to an estimated melt fraction of 5 ± 2%. The depth of this LVZ overlaps with the depth of magma storage estimated from petrology, constraining it with high confidence. Such a combined interdisciplinary study provides valuable information for evaluating future periods of unrest, laying out a framework for the interpretation of incoming monitoring data and signals to look out for in order to improve eruption forecasts.

Seismic Imaging of the Crust Beneath Arunachal Himalaya

AbstractWe present the first high‐resolution seismic images of the crust beneath the Arunachal Himalaya, using 22,525 high quality teleseismic receiver functions (RFs). Data from 32 broadband seismic stations deployed in the Arunachal Himalaya during 2010–2016 is used for this purpose. In addition, data from the HIMNT, SIKKIM, Hi‐CLIMB, and Geodynamics ANd Seismic Structure of the Eastern‐Himalaya Region networks are used to investigate along strike variations in the crustal architecture of the Eastern Himalayan mountain belt. Common Conversions Point stacks constructed using RFs from 203 seismic stations along various S‐N profiles reveal lateral variations in the crustal structure. We observe, (a) a less complex crust beneath the Arunachal Himalaya compared to that in the Nepal and Sikkim Himalaya (b) a highly deformed layer running parallel to the Main Himalayan Thrust (c) intermittent anisotropic low velocity layer in the middle crust (d) that the crustal thickness estimates are in close agreement with those in other segments of the Eastern Himalaya (40–60 kms) (e) no prominent signatures of a mid‐crustal ramp as observed in the Nepal Himalaya. The geometry of the crust in the Eastern Himalayan segments appears less complex compared to the Central Himalayan segments. The presence of strong anisotropy associated with the low velocity layer at depths of 20–30 km suggests a mechanically weak middle crust beneath Arunachal Himalaya. Attributing these anisotropic signatures to the channel flow model appears contentious.

Crustal structure of southeast Australia from teleseismic receiver functions

Abstract. In an effort to improve our understanding of the seismic character of the crust beneath southeast Australia and how it relates to the tectonic evolution of the region, we analyse teleseismic earthquakes recorded by 24 temporary and 8 permanent broadband stations using the receiver function method. Due to the proximity of the temporary stations to Bass Strait, only 13 of these stations yielded usable receiver functions, whereas seven permanent stations produced receiver functions for subsequent analysis. Crustal thickness, bulk seismic velocity properties, and internal crustal structure of the southern Tasmanides – an assemblage of Palaeozoic accretionary orogens that occupy eastern Australia – are constrained by H–κ stacking and receiver function inversion, which point to the following: a ∼ 39.0 km thick crust; an intermediate–high Vp/Vs ratio (∼ 1.70–1.76), relative to ak135; and a broad (> 10 km) crust–mantle transition beneath the Lachlan Fold Belt. These results are interpreted to represent magmatic underplating of mafic materials at the base of the crust. a complex crustal structure beneath VanDieland, a putative Precambrian continental fragment embedded in the southernmost Tasmanides, that features strong variability in the crustal thickness (23–37 km) and Vp/Vs ratio (1.65–193), the latter of which likely represents compositional variability and the presence of melt. The complex origins of VanDieland, which comprises multiple continental ribbons, coupled with recent failed rifting and intraplate volcanism, likely contributes to these observations. stations located in the East Tasmania Terrane and eastern Bass Strait (ETT + EB) collectively indicate a crust of uniform thickness (31–32 km), which clearly distinguishes it from VanDieland to the west. Moho depths are also compared with the continent-wide AusMoho model in southeast Australia and are shown to be largely consistent, except in regions where AusMoho has few constraints (e.g. Flinders Island). A joint interpretation of the new results with ambient noise, teleseismic tomography, and teleseismic shear wave splitting anisotropy helps provide new insight into the way that the crust has been shaped by recent events, including failed rifting during the break-up of Australia and Antarctica and recent intraplate volcanism.

Seismic crustal shear velocity structure across NW Himalaya and Ladakh-Karakoram using receiver function modelling: Evidence of the Main Himalayan Thrust

To understand the nature of the underthrusting Indian Moho and Main Himalayan Thrust across the NW Himalaya and Ladakh-Karakoram (southern Tibet), we calculate the shear velocity models by inverting teleseismic receiver functions at 15 seismic stations. The crustal shear wave velocity models show that the Indian crust underthrusts gently. The depth of Indian Moho increases from ~46 km below the Gangetic Plain to ~78 km at the southern flank of the Karakoram Fault. The crustal velocity models also show a continuous intra-crustal low-velocity layer across the NW Himalaya and Ladakh-Karakoram. We combine our results with earlier results of magnetotelluric and seismological studies in this area. We infer that the observed intra-crustal low-velocity layer from the NW Himalaya to the southern flank of the Karakoram Fault is a possible expression of the Main Himalayan Thrust (MHT) in this region. Moreover, we observe higher shear velocities in the lowermost crust beneath the Higher Himalaya and Ladakh; and interpret them as the possible presence of the (partially) eclogitesed rocks in the lowermost crust.

The lithospheric structure underneath the Circum Black Sea: Teleseismic receiver functions and Rayleigh wave phase velocity analysis

• Lithospheric structure beneath Circum Black Sea is revealed using joint inversion. • Moho depth increases southward from 35 to 40 km along Black Sea coastline. • Lithospheric depth increases southward beneath east of Black Sea (90–130 km). In this paper, the lithospheric structure underneath the Circum Black Sea is investigated on the basis of teleseismic receiver functions and Rayleigh wave phase velocity analyses. A joint inversion of P- and S-wave receiver functions are performed by using an iterative algorithm, similar to the simulated annealing method. The array method is employed to obtain the Rayleigh wave inter-station phase velocity dispersion curves. The dataset recorded during 2010–2020 by sixteen broadband stations, operated by several seismological agencies, includes more than 450 events (Mw ≥ 5.8). The Moho depth increases northward from 35 km to 40 km along both coastlines. Following the velocity models, it is suggested that the crust structure beneath the stations is the continental type. The lithosphere-asthenosphere boundary ranges from ~ 90 km to ~ 120 km from the east coast of the East Black Sea basin, while it is low-sloping (from ~ 100 km to ~ 93 km) for the west coast of the West Black Sea basin, and it is nearly 90 km along with the Pontides. The average P-wave and S-wave velocities inferred from the models indicate the continental lithosphere around the Black Sea coastal region. According to these results, tectonically, it points out that the southward subduction exists in the eastern part of the East Black Sea region beneath the Pontides, while it is not observed in the westernmost Black Sea region.

Crustal structure in the Binchuan basin of Yunnan constrained from receiver functions on a 2-D seismic dense array*

The Binchuan region is located in a seismically active area in northwestern Yunnan, China. The detailed crustal structure is important to understand the tectonic evolution and to assess the seismic hazard in the study area. With a 2-D dense array deployed in this region, we use teleseismic receiver function traditional imaging methods, including the H-κ and common-conversion-point stacking methods, to derive high-resolution crustal thickness and νP/νS ratio maps. Our results indicate that the crustal thickness increases from ~40 km to ~46 km in the south-north direction, and the average crustal thickness beneath the Binchuan basin is ~42 km. Our results agree with previous results but have higher resolution due to dense interstation spacing.

Ps‐P Tomography of a Midcrustal Magma Reservoir Beneath Cleveland Volcano, Alaska

AbstractSeismic tomography of the crust is an essential tool for studying the three‐dimensional structure of magmatic plumbing systems feeding active volcanoes, but it is often limited in resolution by the absence of deep local seismicity. Teleseismic receiver functions can be used to illuminate local structural variations, but typically do not account for the effects of three‐dimensional velocity heterogeneities. Here we harness the complementary strengths of both techniques by processing Ps‐P delay times derived from teleseismic receiver functions in a tomographic S wave inversion. Using our inversion technique, we produce the first tomographic crustal velocity model beneath Cleveland Volcano, identifying a vertically extensive high VP/VS anomaly beneath the volcano that likely signifies a middle‐to‐lower crustal magma reservoir. The observation is the first of its kind in the central Aleutians, illustrating the potential of our technique to advance our understanding of crustal magmatic systems without broad seismic networks or distributed local seismicity.

Seismic evidence for a fossil slab origin for the Isabella anomaly

SUMMARY A teleseismic receiver function image of a slab-like feature that extends from the Pacific coast to the foothills of the Sierra Nevada beneath central California connects the expected location of the subducted remnant of the Monterey microplate to the high-velocity Isabella anomaly in the upper mantle. The observed structure indicates that this anomaly is a relic of the subduction zone that preceded capture of the Monterey microplate by the Pacific plate and is not due to the delamination of the lithosphere beneath the Sierra Nevada Mountains, as had been previously proposed. The fossil slab connection is also supported by surface wave tomographic images. The images are derived in part from a new linear broad-band array across the western part of central California.

Seismological evidence of a dehydration reaction in the subducting oceanic crust beneath western Shikoku in southwest Japan

SUMMARYThe Philippine Sea plate (PHS) is subducting beneath southwest Japan from the Nankai Trough. In this region, deep low-frequency earthquakes/tremors (LFEs) are active and their epicentres are distributed along the downdip of the source region of M8-class earthquakes that have occurred every 100–150 yr. The LFE activity may potentially be strongly related to the occurrence of great earthquakes between tectonic plates. To investigate the structural features around the LFEs, we applied teleseismic receiver function (RF) analysis to the seismograms observed at permanent and temporal seismograph stations in western Shikoku and we detected seismological evidence of a slab dehydration reaction linked to LFE activity. Based on the first-order harmonic decomposition of RFs, we first estimated the average plunge azimuth of the PHS beneath western Shikoku. Considering the backazimuth dependence of converted phase amplitude, we constructed the cross-section of the radial component RFs, excluding the incoming waveform data from the updip directions of the dipping slab. In this profile, the parallel negative and positive P-to-S converted phase alignment within a distance of 10 km were imaged. These phase alignments corresponded to the top of the slab and the slab Moho discontinuity, respectively. At the northern side of the profile, the landward (continental) Moho was also detected. In the region where LFEs were actively distributed, both the landward Moho and slab surface were unclear. The second-order harmonic decomposition of RFs for several kilometres above the slab Moho indicated that the anisotropic symmetry axes suddenly changed at the southern limit of the LFE active region; the fast axes in the region were normal to the trench though axes in the southern area were parallel. According to the thermal and pressure condition, a phase transition with a dehydration reaction can occur in the oceanic crust near the southern edge of the LFE active region. Once the dehydration process advances, released water causes the serpentinization of the mantle material near the slab surface and the corresponding seismic velocity decreases. The impedance contrast decreases at the boundary between the lower crust and the mantle wedge, as well as that between the mantle wedge and oceanic crust; therefore, the amplitudes of the converted phases at these boundaries also become small. Considering that serpentinite ordinarily has strong anisotropy with a seismic fast axis direct to the shear direction, all features observed are evidence of the dehydration process in the flat slab.

Seismicity along the Magallanes-Fagnano fault system

The Magallanes-Fagnano fault (at ~51-56°S) is a continental NW-SE transform fault zone that marks the boundary between the South American Plate (north) and the Scotia Plate (South). In 1949, two crustal seismic events of estimated magnitude M > 7 were located in this area using teleseismic records. Although, this region is scarcely populated, such shallow seismicity could represent a considerable threat to the remote urban centers in this sector. The characterization of the local seismicity always lacked good quality records and permanent instrumentation. In the recent past years, permanent seismic stations (CSN and INPRES-CTBTO) were deployed in the Tierra del Fuego Island and Southern Patagonia, providing with continuous time, broadband records of waveform data. In order to obtain better insights about the local seismicity associated with the Magallanes-Fagnano fault, we jointly inverted teleseismic receiver functions with Rayleigh-wave dispersion data to build a calibrated velocity model for the study region. In parallel, we analyzed the continuous waveforms to automatically detect local earthquakes and locate them using our regional velocity model. Our results show: 1) Shallow seismic events distributed along the Magallanes-Fagnano fault. 2) Diffuse seismicity characterizing the South American crust, north of 53°S. Our observations suggest two mechanisms of crustal deformation. In the Tierra del Fuego Island the seismicity is mostly associated with the Magallanes-Fagnano fault system. In the Southern Patagonia, along the Patagonian Andes the seismicity would be mostly due to isostatic rebound following the retreat of the Patagonian Ice sheet.

Crustal structure across the Deccan Volcanic Province and Eastern Dharwar craton in south Indian shield using receiver function modelling

The south Indian shield, primarily consisting of Archean cratons and Cretaceous-Tertiary Deccan Volcanic Province (DVP), has undergone several major tectonic episodes during its evolution. The Deccan volcanism at Cretaceous-Tertiary (~65 Ma) is the last major tectono-thermal event, which influenced a substantial part of the south Indian shield. To understand the influence of the Deccan volcanism on the evolution of the south Indian shield, we study the crustal seismic structure of the ~65 Ma Deccan Volcanic Province and the adjacent ~2.6 Ga Eastern Dharwar Craton (EDC), which forms the basement of the volcanic terrain. We calculate teleseismic receiver functions for 18 broadband seismic stations along a ~1000 km long seismological profile that cut across both the EDC and DVP. The analysis and modelling, using H-Vp/Vs stacking and generalized neighbourhood algorithm inversion of the receiver functions show distinct crustal structure (crustal thickness, average composition, shear wave velocity variation, nature of crust-mantle boundary, etc.) across the EDC and DVP. The results clearly indicate that the crustal structure is heterogeneous beneath the DVP compared to a relatively uniform structure below the EDC. Using results from this study along with earlier results, we infer that the present Eastern Dharwar Craton terrain is not affected by any tectono-thermal event for a long geological time, including the Deccan volcanism. Whereas, the present Deccan Volcanic Province is highly affected by the Reunion mantle plume-crust interaction.

Crustal Scale Imaging of the Arabia‐Central Iran Collision Boundary Across the Zagros Suture Zone, West of Iran

AbstractWe calculate seismic velocity structure of the north Zagros suture zone, west Iran, to resolve the crustal features at the boundary of Arabian‐Central Iranian collision. We compute teleseismic receiver functions (RFs) for 46 stations along a transect crossing the suture. Through harmonic analysis and inversion of the RF data, we obtain information on the characteristics of the suture zone at depth. The RFs and their harmonics show a low angle NE dipping boundary between the overriding layer and a midcrustal low velocity zone, which corresponds to the suture zone. The overriding high velocity feature (Vs ~ 3.8 km/s) is interpreted as an intermediate depth crustal complex exhumed close to the surface through imbricate thrust faulting and enhanced by crustal buoyancy due to continental underthrusting. Significant anisotropy is found above and below the suture zone: We interpret it in terms of slow‐symmetry‐axis anisotropy and derive clues on the ongoing deformation processes.

Crustal Structure Beneath KLNI Station in Lombok Island Based on Teleseismic Receiver Function

Lombok Island is part of the Sunda-Banda arc system which is one of the most active tectonic regions in the world. In Lombok area there are two subduction zones namely Java trench in the south and Flores back arc thrust in the north. Information on crustal structure is needed to explain the tectonic development and geodynamic interaction of the area. The receiver function is one of the techniques used in the study to identify subsurface and wave velocity structures based on earthquake data regardless of the source mechanism. We analyzed receiver function of teleseismic events (epicenter distance 30-90°) and magnitude more than 6 (M>6) to estimate crustal thickness, Vp/Vs ratio and wave velocity structure beneath KLNI station using H-κ stacking and inversion method. We obtained that the crustal thickness and Vp/Vs ratio beneath KLNI station is about 21.38 km and 2.05. The high Vp/Vs ratio might be an indication of partial melting related to the upwelling of hot asthenosphere material through the subduction slab of Java Trench. The depth of the low velocity zone beneath KLNI station is at 10-18 km which is estimated due to the presence of geothermal

A new method to estimate ocean-bottom-seismometer orientation using teleseismic receiver functions

SUMMARYThe orientation of an ocean-bottom-seismometer (OBS) is a critical parameter for analysing three-component seismograms, but it is difficult to estimate because of the uncontrollable OBS posture after its deployment. In this study, we develop a new and effective method to estimate the OBS orientation by fitting the amplitude of direct P wave of teleseismic receiver functions. The reliability of this method is verified using synthetic data and observed waveforms recorded at land seismic stations in Shandong Province, China. Our extensive synthetic tests show that our new method is little affected by a thin sedimentary layer that has a low S-wave velocity. The orientations of OBS stations that we deployed in the Yap subduction zone in the Western Pacific Ocean are estimated and corrected using our new method. After the correction, the direct P waves of teleseismic receiver functions show very good consistency. The effects of white and coloured noise in different levels, epicentral distance and backazimuth are also investigated, and the results show that these factors have small effects on the new method. We also examine the effect of sensor tilting on estimation of the OBS orientation, and find that a tilting correction should be made before the misorientation correction. We compare the OBS orientations determined with the new method and other methods and find that they are generally consistent with each other. We also discuss advantages and shortcomings of various methods, and think that our new method is more robust than the existing methods.

Crustal shear-wave velocity structure in Western Java, Indonesia from analysis of teleseismic receiver functions

We analysed receiver functions from teleseismic events recorded at 11 broadband seismometers in the western part of Java Island, Indonesia. The stations are mostly located at three main geological environment including Northwest Java Basin, Bogor Zone, and Southern Mountains Arc. A total of about 341 receiver functions were computed using iterative time domain deconvolution. We derived shear-wave velocity structure and crustal Vp/Vs ratio by inverting stacked radial receiver functions using non-linear neighbourhood algorithm. Inversion results show sediment thickness varies between 1 and 2 km thick in Western Java. Our inversion shows that crustal thickness in this region varies between 25 and 32 km. Average crustal Vp/Vs ratio is estimated to be about 1.69–1.78. We hope the study may provide useful information for velocity model and crustal thickness for Indonesia region.

Southern Chile crustal structure from teleseismic receiver functions: Responses to ridge subduction and terrane assembly of Patagonia

AbstractContinental crustal structure is the product of those processes that operate typically during a long tectonic history. For the Patagonia composite terrane, these tectonic processes include its early Paleozoic accretion to the South America portion of Gondwana, Triassic rifting of Gondwana, and overriding of Pacific Basin oceanic lithosphere since the Mesozoic. To assess the crustal structure and glean insight into how these tectonic processes affected Patagonia, we combined data from two temporary seismic networks situated inboard of the Chile triple junction, with a combined total of 80 broadband seismic stations. Events suitable for analysis yielded 995 teleseismic receiver functions. We estimated crustal thicknesses using two methods, the H-k stacking method and common conversion point stacking. Crustal thicknesses vary between 30 and 55 km. The South American Moho lies at 28–35 km depth in forearc regions that have experienced ridge subduction, in contrast to crustal thicknesses ranging from 34 to 55 km beneath regions north of the Chile triple junction. Inboard, the prevailing Moho depth of ∼35 km shallows to ∼30 km along an E-W trend between 46.5°S and 47°S; we relate this structure to Paleozoic thrust emplacement of the Proterozoic Deseado Massif terrane above the thicker crust of the North Patagonian/Somún Cura terrane along a major south-dipping fault.

Structure‐Coupled 3‐D Imaging of Magnetotelluric and Wide‐Angle Seismic Reflection/Refraction Data With Interfaces

AbstractMagnetotelluric (MT) and wide‐angle seismic reflection/refraction surveys play a fundamental role in understanding the crustal rheology and lithospheric structure of the Earth. In recent years, the integration of the two methods in order to improve the robustness of the inversion has started to gain attention. We present a new approach for joint 3‐D inversion of MT and wide‐angle seismic reflection/refraction data to accurately determine crustal structures and Moho depth. Based on H‐κ stacking of teleseismic receiver functions, we estimate an initial reference Moho. This is used as input for the subsequent MT/seismic joint inversion, where the Moho interface is updated and crustal structures are added to the model. During the joint inversion process, structural similarity is facilitated through the cross‐gradient constraint. Synthetic model tests show an improvement of the inversion results over separate inversions. In particular, the tests based on two geologically realistic models demonstrate that the crustal structure and even the trade‐off between velocity and Moho interface can be sufficiently resolved by combined MT and seismic data sets when using the estimates from analysis of receiver functions. These results show that the new method can provide useful constraints on crustal structures including their geophysical properties and discontinuities.

Deep Crustal Faults, Shear Zones, and Magmatism in the Eastern Cordillera of Colombia: Growth of a Plateau From Teleseismic Receiver Function and Geochemical Mio‐Pliocene Volcanism Constraints

AbstractThe Eastern Cordillera of Colombia, in the northern Andes, is an example of an orogen in which Mesozoic basins were compressed during the Cenozoic, forming a ~2,500‐m‐high plateau in its northern portion. Significant shortening and crustal thickening have contributed to the construction of the present topography and elevation. In this contribution, we combine the use of teleseismic receiver functions, Hf isotopes, whole‐rock geochemistry, and U‐Pb dating to help elucidate the main mechanisms that played a role in the crustal thickening and uplift of the cordillera. Receiver functions calculated for three stations on top of the plateau are consistent with the presence of thrusts that converge into major crustal interfaces at upper‐middle crustal depths; they also suggest the existence of two crustal anisotropic layers beneath the western flank of the cordillera, which we interpret to have formed as a result of shearing. In the northern portion of the plateau, in the area where two Mio‐Pliocene volcanic domes and their related deposits outcrop, a lower crustal high seismic velocity layer is suggested by the receiver functions; we propose magmatic underplating for the origin of this layer. The geochemical characteristics of the volcanic rocks in the area are consistent with partial melt in a mantle influenced by slab‐related fluids; this magma could have been added to the crust and portions of it ascended and reached the surface, experiencing assimilation and differentiation during the process. We hypothesize that this Mio‐Pliocene volcanism was related to flattening of the Nazca subducting slab.

A reappraisal of the H–κ stacking technique: implications for global crustal structure

SUMMARYH–κ stacking is used routinely to infer crustal thickness and bulk-crustal VP/VS ratio from teleseismic receiver functions. The method assumes that the largest amplitude P-to-S conversions beneath the seismograph station are generated at the Moho. This is reasonable where the crust is simple and the Moho marks a relatively abrupt transition from crust to mantle, but not if the crust–mantle transition is gradational and/or complex intracrustal structure exists. We demonstrate via synthetic seismogram analysis that H–κ results can be strongly dependent on the choice of stacking parameters (the relative weights assigned to the Moho P-to-S conversion and its subsequent reverberations, the choice of linear or phase-weighted stacking, input crustal P-wave velocity) and associated data parameters (receiver function frequency content and the sample of receiver functions analysed). To address this parameter sensitivity issue, we develop an H–κ approach in which cluster analysis selects a final solution from 1000 individual H–κ results, each calculated using randomly selected receiver functions, and H–κ input parameters. 10 quality control criteria that variously assess the final numerical result, the receiver function data set, and the extent to which the results are tightly clustered, are used to assess the reliability of H–κ stacking at a station. Analysis of synthetic data sets indicates H–κ works reliably when the Moho is sharp and intracrustal structure is lacking but is less successful when the Moho is gradational. Limiting the frequency content of receiver functions can improve the H–κ solutions in such settings, provided intracrustal structure is simple. In cratonic Canada, India and Australia, H–κ solutions generally cluster tightly, indicative of simple crust and a sharp Moho. In contrast, on the Ethiopian plateau, where Palaeogene flood-basalts overlie marine sediments, H–κ results are unstable and erroneous. For stations that lie on thinner flood-basalt outcrops, and/or in regions where Blue Nile river incision has eroded through to the sediments below, limiting the receiver function frequency content to longer periods improves the H–κ solution and reveals a 6–10 km gradational Moho, readily interpreted as a lower crustal intrusion layer at the base of a mafic (VP/VS = 1.77–1.87) crust. Moving off the flood-basalt province, H–κ results are reliable and the crust is thinner and more felsic (VP/VS = 1.70–1.77), indicating the lower crustal intrusion layer is confined to the region covered by flood-basaltic volcanism. Analysis of data from other tectonically complex settings (e.g. Japan, Cyprus) shows H–κ stacking results should be treated cautiously. Only in regions of relatively simple crust can H–κ stacking analysis be considered truly reliable.