First seismic constraints on the Martian crust – receiver functions for InSight

NASA&#8217;s InSight mission arrived on Mars in November 2018 and deployed the first very broad-band seismometer, SEIS, on the planet&#8217;s surface. SEIS has been collecting data continuously since early February 2019, by now recording more than 400 events of different types. InSight aims at enhancing our understanding of the internal structure and dynamics of Mars, including better constraints on its crustal thickness. Various models based on topography and gravity observed from the orbit currently vary in average crustal thickness from 30 km to more than 100 km, with important implications for Mars&#8217; thermal evolution, and the partitioning of silicates and heat-producing elements between different layers of Mars.We present P-to-S and S-to-P receiver functions, which are available for 4 and 3 marsquakes, respectively, up to now. Out of all of the marsquakes recorded to date, these are the only ones with clear enough P- or S-arrivals not dominated by scattering to make them suitable for the analysis. All of the quakes are located at comparatively small epicentral distances, between 25&#176; and 40&#176;. We observe three consistent phases within the first 10 seconds of the P-to-S receiver functions. The S-to-P receiver functions also show a consistent first phase. Later arrivals are harder to pinpoint, which could be due to the comparatively shallow incidence of the S-waves at the considered distances, which prevents the generation of converted waves. Identification of later multiple phases in the P-to-S receiver functions likewise remains inconclusive. To obtain better constraints on velocity, we also calculated apparent velocity curves from the P-to-S receiver functions, but these provide meaningful results for only one event so far, implying a large uncertainty. Due to difficulties in clearly identifying multiples, the receiver functions can currently be explained by either two crustal layers and a thin (25-30 km) crust or three crustal layers and a thicker (40-45 km) crust at the landing site. This model range already improves the present constraints by providing a new maximum value of less than 70 km for the average crustal thickness. Information from noise autocorrelations as a complementary method, identification of P-reverberations and S-precursors in the event recordings, and more extensive modeling, ultimately including 3D-effects, are considered to further our understanding of the waveforms and tighten the constraints on the crust.

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Joint inversion of receiver functions and apparent incidence angles to investigate the crustal structure of Mars

10.5194/egusphere-egu21-9470 ◽

2021 ◽

Author(s):

Rakshit Joshi ◽

Brigitte Knapmeyer-Endrun ◽

Klaus Mosegaard ◽

Felix Bissig ◽

Amir Khan ◽

...

Keyword(s):

Wave Velocity ◽

Crustal Structure ◽

Joint Inversion ◽

Landing Site ◽

Crustal Thickness ◽

Receiver Functions ◽

P Wave ◽

S Wave ◽

Data Set ◽

Insight Mission

Since InSight (the Interior Exploration using Geodesy and Heat Transport) landed 26 months ago and deployed an ultra sensitive broadband seismometer(SEIS) on the surface of Mars, around 500 seismic events of diverse variety have been detected, making it possible to directly analyze the subsurface properties of Mars for the very first time. One of the primary goals of the mission is to retrieve the crustal structure below the landing site. Current estimates differ by more than 100% for the average crustal thickness. Since data from orbital gravity measurementsprovide information on relative variations of crustal thickness but not absolute values, this landing site measurement could serve as a tie point to retrieve global crustal structure models. To do so, we propose using a joint inversion of receiver functions and apparent incidence angles, which contain information on absolute S-wave velocities of the subsurface. Since receiver function inversions suffer from a velocity depth trade-off, we in addition exploit a simple relation which defines apparent S-wave velocity as a function of observed apparent P-wave incidence angles to constrain the parameter space. Finally we use the Neighbourhood Algorithm for the inversion of a suitable joint objective function. The resulting ensemble of models is then used to derive the full uncertainty estimates for each model parameter. Before its application on data from InSight mission, we successfully tested the method on Mars synthetics and terrestrial data from various geological settings using both single and multiple events. Using the same method, we have previously been able to constrain the S-wave velocity and depth for the first inter-crustal layer of Mars between 1.7 to 2.1 km/s and 8 to 11 km, respectively. Here we present the results of applying this technique on our selected data set from the InSight mission. Results show that the data can be explained equally well by models with 2 or 3 crustal layers with constant velocities. Due to the limited data set it is difficult to resolve the ambiguity of this bi-modal solution. We therefore investigate information theoretic statistical tests as a model selection criteria and discuss their relevance and implications in seismological framework.<div></div><div></div><div></div>

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Crustal structure variations in south-central Mexico from receiver functions

Geophysical Journal International ◽

10.1093/gji/ggz434 ◽

2019 ◽

Vol 219 (3) ◽

pp. 2174-2186

Author(s):

Miguel Rodríguez-Domínguez ◽

Xyoli Pérez-Campos ◽

Conrado Montealegre-Cázares ◽

Robert W Clayton ◽

Enrique Cabral-Cano

Keyword(s):

Gulf Of Mexico ◽

Pacific Coast ◽

Broad Band ◽

Crustal Thickness ◽

Receiver Functions ◽

Central Mexico ◽

Intrinsic Mode Functions ◽

S Wave ◽

South Central ◽

The Pacific

Summary Mexico has a complex geological history that is typified by the distinctive terranes that are found in the south-central region. Crustal thickness variations often correlate with geological terranes that have been altered by several processes in the past, for example aerial or subduction erosion, underplating volcanic material or rifting but few geophysical studies have locally imaged the entire continental crust in Mexico. In this paper, the thickness of three layers of the crust in south-central Mexico is determined. To do this, we use P- and S-wave receiver functions (RF) from 159 seismological broad-band stations. Thanks to its adaptive nature, we use an empirical mode decomposition (EMD) algorithm to reconstruct the RFs into intrinsic mode functions (IMF) in order to enhance the pulses related to internal discontinuities within the crust. To inspect possible lateral variations, the RFs are grouped into quadrants of 90°, and their amplitudes are mapped into the thickness assuming a three-layer model. Using this approach, we identify a shallow sedimentary layer with a thickness in the range of 1–4 km. The upper-crust was estimated to be of a few kilometers (<10 km) thick near the Pacific coast, and thicker, approximately 15 km in central Oaxaca and under the Trans-Mexican Volcanic Belt (TMVB). Close to the Pacific coast, we infer a thin crust of approximately 16 ± 0.9 km, while in central Oaxaca and beneath the TMVB, we observe a thicker crust ranging between 30 and 50 km ± 2.0 km. We observe a crustal thinning, of approximately 6 km, from central Oaxaca (37 ± 1.9 km) towards the Gulf of Mexico, under the Veracruz Basin, where we estimate a crustal thickness of 31.6 ± 1.9 km. The boundary between the upper and lower crust in comparison with the surface of the Moho do not show significant variations other than the depth difference. We observe small crustal variations across the different terranes on the study area, with the thinnest crust located at the Pacific coast and Gulf of Mexico coast. The thickest crust is estimated to be in central Oaxaca and beneath the TMVB.

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China's Chang'e-5 Landing Site: An Overview

10.5194/egusphere-egu21-1615 ◽

2021 ◽

Author(s):

Yuqi Qian ◽

Long Xiao ◽

James Head ◽

Carolyn van der Bogert ◽

Harald Hiesinger ◽

...

Keyword(s):

Thermal Evolution ◽

Source Region ◽

Landing Site ◽

Volcanic Complex ◽

The Moon ◽

Age Variations ◽

Specific Source ◽

Scientific Significance ◽

Lunar Chronology ◽

Mare Basalts

IntroductionThe Chang&#8217;e-5 (CE-5) mission is China&#8217;s first lunar sample return mission. CE-5 landed at Northern Oceanus Procellarum (43.1&#176;N, 51.8&#176;W) on December 1, 2020, collected 1731 g of lunar samples, and returned to the Earth on December 17, 2020. The CE-5 landing site is ~170 km ENE of Mons R&#252;mker [1], characterized by some of the youngest mare basalts (Em4/P58) on the Moon [2,3], which are never sampled by the Apollo or Luna missions [4]. This study describes the geologic background of the CE-5 landing site in order to provide context for the ongoing sample analysis.Northern Oceanus ProcellarumNorthern Oceanus Procellarum is in the northwest lunar nearside, and the center of the Procellarum-KREEP-Terrane [5], characterized by elevated heat-producing elements and prolonged volcanism. This region exhibits a huge volcanic complex, i.e., Mons R&#252;mker [1], and two episodes of mare eruptions, i.e., Imbrian-aged low-Ti mare basalts in the west and Eratosthenian-aged high-Ti mare basalts (Em3 and Em4/P58) in the east [2]. The longest sinuous rille on the Moon [6], Rima Sharp, extends across Em4/P58. Both the Imbrian-aged (NW-SE) and Eratosthenian-aged (NE-SW) basalts display wrinkle ridges, indicating underlying structures, with different dominant orientations [2].Young Mare BasaltsThe Em4/P58 mare basaltic unit, on which CE-5 landed, is one of the youngest mare basalts on the Moon. Various researchers found different CSFD results; however, all of them point to an Eratosthenian age for Em4/P85 (1.21 Ga [2], 1.33 Ga [7,8], 1.53 Ga [3], 1.91 Ga [9]), and there are minor age variations across Em4/P58 [3]. Em4/P58 mare basalts have high-Ti, relatively high-olivine and high-Th abundances, while clinopyroxene is the most abundant mineral type [2,3]. Em4/P58 mare basalts cover an area of ~37,000 km2, with a mean thickness of ~51 m and volume of ~1450-2350 km3 [3]. No specific source vents were found within the unit, and Rima Sharp is the most likely source region for the Em4/P58 mare basalts [3].Scientific Significance of the Returned SamplesThe scientific significance of the young mare basalts is summarized in our previous studies [2,3]. In [3], we first summarized the 27 fundamental questions that may be answered by the returned CE-5 samples, including questions about chronology, petrogenesis, regional setting, geodynamic & thermal evolution, and regolith formation (Tab. 1 in [3]), especially calibrating the lunar chronology function, constraining the lunar dynamo status, unraveling the deep mantle properties, and assessing the Procellarum-KREEP-Terrain structures.References[1] Zhao J. et al. (2017) JGR, 122, 1419&#8211;1442. [2] Qian Y. et al (2018) JGR, 123, 1407&#8211;1430. [3] Qian Y. et al. (2021) EPSL, 555, 116702. [4] Tart&#232;se R. et al. (2019) Space Sci. Rev., 215, 54. [5] Jolliff B. L. et al. (2000) JGR, 105, 4197&#8211;4216. [6] Hurwitz D. M. et al. (2013) Planet. Space Sci., 79&#8211;80, 1&#8211;38. [7] Hiesinger H. et al. (2003) JGR, 108, 1&#8211;1 (2003). [8] Hiesinger H. et al. (2011) Geol. Soc. Am., 477, 1&#8211;51. [9] Morota T. et al. (2011) EPSL, 302, 255&#8211;266.

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Scaling laws for stagnant-lid convection with a buoyant crust

Geophysical Journal International ◽

10.1093/gji/ggab366 ◽

2021 ◽

Vol 228 (1) ◽

pp. 631-663

Author(s):

Kyle Batra ◽

Bradford Foley

Keyword(s):

Heat Flux ◽

Scaling Laws ◽

Thermal Evolution ◽

Crustal Thickness ◽

Plate Motion ◽

Crustal Layer ◽

Lithospheric Thickness ◽

Thin Crust ◽

Mantle Temperature ◽

Thick Crust

SUMMARY Stagnant-lid convection, where subduction and surface plate motion is absent, is common among the rocky planets and moons in our solar system, and likely among rocky exoplanets as well. How stagnant-lid planets thermally evolve is an important issue, dictating not just their interior evolution but also the evolution of their atmospheres via volcanic degassing. On stagnant-lid planets, the crust is not recycled by subduction and can potentially grow thick enough to significantly impact convection beneath the stagnant lid. We perform numerical models of stagnant-lid convection to determine new scaling laws for convective heat flux that specifically account for the presence of a buoyant crustal layer. We systematically vary the crustal layer thickness, crustal layer density, Rayleigh number and Frank–Kamenetskii parameter for viscosity to map out system behaviour and determine the new scaling laws. We find two end-member regimes of behaviour: a ‘thin crust limit’, where convection is largely unaffected by the presence of the crust, and the thickness of the lithosphere is approximately the same as it would be if the crust were absent; and a ‘thick crust limit’, where the crustal thickness itself determines the lithospheric thickness and heat flux. Scaling laws for both limits are developed and fit the numerical model results well. Applying these scaling laws to rocky stagnant-lid planets, we find that the crustal thickness needed for convection to enter the thick crust limit decreases with increasing mantle temperature and decreasing mantle reference viscosity. Moreover, if crustal thickness is limited by the formation of dense eclogite, and foundering of this dense lower crust, then smaller planets are more likely to enter the thick crust limit because their crusts can grow thicker before reaching the pressure where eclogite forms. When convection is in the thick crust limit, mantle heat flux is suppressed. As a result, mantle temperatures can be elevated by 100 s of degrees K for up to a few Gyr in comparison to a planet with a thin crust. Whether convection enters the thick crust limit during a planet’s thermal evolution also depends on the initial mantle temperature, so a thick, buoyant crust additionally acts to preserve the influence of initial conditions on stagnant-lid planets for far longer than previous thermal evolution models, which ignore the effects of a thick crust, have found.

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Sharpness of the 410-km discontinuity from the P410s and P2p410s seismic phases

Geophysical Journal International ◽

10.1093/gji/ggz507 ◽

2019 ◽

Cited By ~ 1

Author(s):

Lev Vinnik ◽

Yangfan Deng ◽

Grigoriy Kosarev ◽

Sergey Oreshin ◽

Zhou Zhang ◽

...

Keyword(s):

Transition Zone ◽

Southern Africa ◽

Amplitude Ratio ◽

Southern China ◽

Broad Band ◽

Receiver Functions ◽

P Wave ◽

Seismic Model ◽

Yangtze Craton ◽

Zone Water

Summary Sharpness of the 410-km boundary is of interest because it is sensitive to water content in the transition zone. We evaluate the width of the 410-km discontinuity with a new seismic method. Our estimates are inferred from the amplitude ratio of the P2p410s and P410s seismic phases that are detected in P-wave receiver functions. We applied this method to seismic recordings from arrays of broad-band stations deployed in central Fennoscandia, southern Africa and southern China. The obtained estimates of width of the 410-km discontinuity range from 10 to 22 km and always exceed the width of 7 km which is expected for anhydrous conditions. The enlarged width may be interpreted in terms of hydrous conditions, but we have found only one region (the eastern Yangtze Craton in China) where the broad 410-km discontinuity, as expected, is accompanied by a broad transition zone. Water in the transition zone may be a kind of a global phenomenon, but evidence of the enlarged width of the transition zone may be missing in most of our data because the reference seismic model is affected by water, as well.

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Simultaneous inversion for crustal thickness and anisotropy by multiphase splitting analysis of receiver functions

Geophysical Journal International ◽

10.1093/gji/ggaa435 ◽

2020 ◽

Vol 223 (3) ◽

pp. 2009-2026

Author(s):

Frederik Link ◽

Georg Rümpker ◽

Ayoub Kaviani

Keyword(s):

Statistical Tests ◽

Real Data ◽

Crustal Thickness ◽

Receiver Functions ◽

S Wave ◽

Arrival Times ◽

Simultaneous Inversion ◽

Correction Scheme ◽

Converted Phases ◽

Two Phases

SUMMARY We present a technique to derive robust estimates for the crustal thickness and elastic properties, including anisotropy, from shear wave splitting of converted phases in receiver functions. We combine stacking procedures with a correction scheme for the splitting effect of the crustal converted Ps-phase and its first reverberation, the PpPs-phase, where we also allow for a predefined dipping Moho. The incorporation of two phases stabilizes the analysis procedure and allows to simultaneously solve for the crustal thickness, the ratio of average P- to S-wave velocities, the percentage of anisotropy and the fast-axis direction. The stacking is based on arrival times and polarizations computed using a ray-based algorithm. Synthetic tests show the robustness of the technique and its applicability to tectonic settings where dip of the Moho is significant. These tests also demonstrate that the effects of a dipping layer boundary may overprint a possible anisotropic signature. To constrain the uncertainty of our results we perform statistical tests based on a bootstrapping approach. We distinguish between different model classes by comparing the coherency of the stacked amplitudes after moveout correction. We apply the new technique to real-data examples from different tectonic regimes and show that coherency of the stacked receiver functions can be improved, when anisotropy and a dipping Moho are included in the analysis. The examples underline the advantages of statistical analyses when dealing with stacking procedures and potentially ambiguous solutions.

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