Imaging the Upper Plate Lithosphere and Asthenosphere beneath Alaska with Sp Converted Waves

2021 ◽  
Author(s):  
Isabella Gama ◽  
Karen M. Fischer ◽  
Junlin Hua
Keyword(s):  
Free Surface ◽  
Velocity Gradient ◽  
Mantle Wedge ◽  
Seismic Velocity ◽  
Receiver Functions ◽  
The North ◽  
West Central ◽  
Subduction Zone Processes ◽  
The Us ◽  
Moho Depths

<p>To resolve the signatures of subduction zone processes in the mantle wedge, and how subduction has interacted with the upper plate, we imaged seismic velocity gradients beneath the US state of Alaska with Sp receiver function common conversion point (CCP) stacking.  Pacific plate lithosphere, and lithosphere bearing the thicker crust of the Yakutat terrane, subduct to the northwest beneath the southern margin of Alaska.   We employed data from hundreds of stations of the US NSF EarthScope Transportable Array, as well as other portable arrays and permanent networks. We calculated waveform components using a free-surface transform with improved estimates of free-surface velocities that were determined from P and SV particle motions. Sp receiver functions were calculated with time-domain deconvolution, and the CCP stack was generated with weighting functions that incorporate the properties of Sp scattering kernels. The CCP stack shows a clear interface between the North American and underthrust Yakutat crust, as well as Yakutat Moho depths of up to 60 km.  Sp phases from the negative velocity gradient at the base of the upper plate are strongest in west-central Alaska, where lithosphere-asthenosphere boundary (LAB) depths lie at 65-100 km.  In west-central Alaska, joint inversions of Sp data at single stations with Rayleigh phase velocities show comparable LAB depths as well as low asthenospheric velocities. This zone includes active magmatism and the upper plate appears to have been thinned by mantle wedge volatiles, melt, and flow.  The LAB phase deepens to the north, reaching depths of ~120 km beneath the northern Arctic Alaska terrane.  This increase in the depth of the LAB phase from the arc to the back-arc is consistent with the sculpting of the upper plate by subduction-related processes. Sp phases also delineate a prominent positive velocity gradient that represents the base of a low-velocity asthenospheric layer at depths of 100-130 km.  The positive velocity gradient is consistent with the onset of partial melting in the asthenosphere.</p><p> </p>

Deep deformation process of the NE Tibetan Plateau: evidence from receiver function imaging

2020 ◽  
Author(s):  
yifang chen ◽  
jiuhui chen
Keyword(s):  
Tibetan Plateau ◽  
Seismic Velocity ◽  
Receiver Function ◽  
Decisive Role ◽  
Deformation Mode ◽  
Receiver Functions ◽  
Tibet Plateau ◽  
The Tibetan Plateau ◽  
Waveform Data ◽  
The North

<p>The deformation of Qilian Orogenic Belt, which is the uplifting front of the northeastern Tibet Plateau, plays a decisive role in understanding the dynamic process of the area uplift. Many of the tectonic processes models of the Tibetan Plateau growth, which are based on geophysical and geological studies, have been conducted in recent years. However, the deformation mode of northeastern Tibetan Plateau (NETP) remains controversial for lack of sufficient proofs. We used teleseismic waveform data collected from the China Array seismic experiment during 2013-2015 and QL temporary stations during 2016-2017. In this study, we used the 3-D Common Conversion Point (CCP) technique (with the P/S receiver functions) to obtain detailed seismic velocity discontinuities structure of lithosphere beneath the NETP and Alxa block. Our preliminary results can be summarized as follows: 1) The Lithosphere asthenosphere boundary (LAB) lies at a depth pf 110-140 km in Alxa platform, deepens below the North Qilian mountain (160-170 km ) which has been inserted by lithosphere of Central Qilian, between the South Qilian suture zone (SQL) and the north of the Songpan-Ganzi Terranes (160-170 km). 2) The main features in the crust include offset of Moho beneath NQLF, shallower crust thickness below between the NQLF and LSSF and a continuous positive interface over the Moho in the north of the LSSF. 3) According to our observation and previous studies, we suppose that lithosphere had been passive underthrust and localized crust had been shortened and thickened in the NETP.</p>

Crustal attenuation from USArray ML amplitude tomography

2020 ◽  
Vol 224 (1) ◽  
pp. 199-206
Author(s):  
Thomas M Hearn
Keyword(s):  
Seismic Velocity ◽  
Gulf Coast ◽  
Sedimentary Basins ◽  
Volcanic Field ◽  
Seismic Attenuation ◽  
High Attenuation ◽  
The North ◽  
Western Us ◽  
Geothermal Activity ◽  
The Us

SUMMARY Seismic attenuation across the US is estimated using station ML magnitude data from the USArray. Station magnitudes are recalibrated back to amplitude and back projected in a 2-D tomography. Data represent the amplitudes of the horizontal components of the Lg phase. The western US shows regions of very high attenuation and contrasts with the lesser attenuation of the eastern US. Individual attenuation anomalies can be clearly tied to regional geology. Station gains show broad regional variations that match geographic regions. Most of the high-attenuation areas are regions of high geothermal activity suggesting that intrinsic attenuation dominates over scattering attenuation. An exception is the central San Andreas Fault zone because it lacks any localized heat-flow anomaly. The US east of the Rocky Mountains is bland and contains none of the high-attenuation regions of the western US. Instead, the central US has low-attenuation patches that do not obviously correspond to geologic province. Sediments of the Gulf Coast Plain, Willison Basin and Michigan Basin do show up as intermediate attenuation while the Illinois Basin, Appalachian Basin and other basins are not apparent. In Alaska, attenuation is generally less than the western US, but still much greater than the eastern US. In southeast Alaska, the Wrangell Volcanic Field causes a sizeable high-attenuation zone. The volcanic Aleutian Mountains also have high attenuation. However, moderate to high attenuation also correlates with the tertiary sedimentary basins in Alaska. The North Slope Basin does not seem to attenuate. Thicker crust and mountain roots tend to show less attenuation, if anything, but this correspondence is most likely due to differences in temperature and seismic velocity. Heat, scattering and young sedimentary basins create seismic attenuation in the continental crust.

scholarly journals Crustal structure of southeast Australia from teleseismic receiver functions

Solid Earth ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 463-481
Author(s):  
Mohammed Bello ◽  
David G. Cornwell ◽  
Nicholas Rawlinson ◽  
Anya M. Reading ◽  
Othaniel K. Likkason
Keyword(s):  
Crustal Structure ◽  
Seismic Velocity ◽  
Receiver Function ◽  
Crustal Thickness ◽  
Receiver Functions ◽  
Teleseismic Tomography ◽  
Intraplate Volcanism ◽  
Southeast Australia ◽  
Eastern Australia ◽  
Moho Depths

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.

Экологическое испытание гибрида огурца F1 Энеж 21 в открытом грунте

2018 ◽  
Author(s):  
L.A. Chistyakova ◽  
O.V. Baklanova ◽  
E.L. Makarova ◽  
Yu.V. Bortsova
Keyword(s):  
Russian Federation ◽  
High Potential ◽  
Moscow Region ◽  
North West ◽  
The North ◽  
Pickling Cucumber ◽  
West Central ◽  
Open Ground ◽  
Chuvash Republic ◽  
The Russian Federation

Приведены результаты испытания нового перспективного партенокарпического гибрида огурца корнишонного типа F1 Энеж 21, созданного селекционерами агрохолдинга «Поиск», в условиях открытого грунта в Северо-Западном, Центральном и Волго-Вятском регионах Российской Федерации: Костромская, Ярославская, Московская, Рязанская, Тульская область и Чувашская Республика. Высокие потенциальные возможности и адаптационные свойства гибрида F1 Энеж 21 наиболее значимо проявляются в Московской области (63,8 т/га), Чувашской Республике (39,4 т/га) и Рязанской области (31,2 т/га).The article presents the results of testing a new promising parthenocarpic pickling cucumber hybrid F1 Enezh 21, selected by the breedrs of the Agricultural holding «Poisk» in conditions of open ground in the North-West, Central and Volga-Vyatka regions of the Russian Federation: Kostroma, Yaroslavl, Moscow, Ryazan, Tula regions and the Chuvash Republic. The high potential and adaptation characteristic of the F1 Enezh 21 hybrid are most significantly presented in condition of the Moscow region (63.8 t / ha), the Chuvash Republic (39.4 t / ha) and the Ryazan region (31.2 t / ha).

The Tragedy of Lebanon

1984 ◽  
Vol 1 (1) ◽  
pp. 27-52
Author(s):  
Mahmud A. Faksh
Keyword(s):  
Civil War ◽  
Status Quo ◽  
World War ◽  
Land Area ◽  
Henry Kissinger ◽  
The North ◽  
Northern Cyprus ◽  
The Us ◽  
The Status ◽  
New States

I.Since the end of World War 11, approximately eighty new states havebeen established. Only two, Pakistan and Cyprus, have undergone theagony of dismemberment when Bangladesh broke off in 1973 and theTurkish Republic of Northern Cyprus was declared in 1983. The worldmay now be witnessing the possible breakup of yet a third state:Lebanon, whose disintegration has been accelerated since the June 1982Israeli invasion.Shortly after the invasion began, Henry Kissinger assessed itsconsequence for Lebanon’s future, concluding, “It is neither desirablenor possible to return to the status quo ante in Lebanon.” One possibleoutcome was that some Syrian and Israeli forces would remain in thenorthern and southern ends, respectively, and the central government’sauthority would ostensibly cover the rest of the country. Implicit in theKissinger diagnosis is the possibility of eventual partition.Though the gloomy assessment by the “wizard” of US. foreign policyshould by no means be construed as a portent of an official shift awayfrom the publicly stated US. support of “Lebanon’s sovereignty andterritorial integrity,” a shadow was cast on the country’s prospects.Subsequent developments have seemed to indicate that Lebanon’sdemise looms larger than at any time since the beginning of the civil warin 1975-76.For over a year and a half national fragmentation has proceededinexorably. What many people once could imagine only with difficulty,they now acknowledge: in reality, Lebanon is facing possible death. TheSouth (35 percent of the land area) is occupied by Israel; the North andthe Biqa’ (45 percent) are controlled by Syria; Kasrawan (15 percent) iscontrolled by the Christian Maronite forces (the Lebanese Front forces),which are not subject to the government’s authority. The rest of thecountry-beleaguered Beirut and environs-was until the February1984 breakdown under the government’s shaky control supported bysymbolic US., French, Italian, and British units. The Multi-NationalForce (MNF) was subject to increasing attacks by Muslim leftist factions,as witnessed in the October 23 bombing of the quarters of U.S.Marines and French troops. Thus, instead of keeping peace, the MNFbecame ,a partisan force trying to protect itself. The US. and Frenchforces in particular seemed to have outlived their usefulness as“peacekeepers.” Recurrent fighting in southern Beirut and in theadjacent Chouf mountains, that pitted Christian Maronites and armyunits against Shi‘ite and Druse Muslims constantly threatened theexistence of President Amin Gemayel’s government and consequently arenewal of the civil war. This situation culminated in February 1984 inthe resignation of the Shafiq al-Wazzan’s cabinet, the loss ofgovernment’s control of West Beirut to Muslim-leftist militias, and theimminent collapse of Amin Gemayel’s presidency ...

Uncommon Grounds

2017 ◽  
Author(s):  
Jeffrey Lawrence
Keyword(s):  
American Literature ◽  
Latin American ◽  
Historical Novel ◽  
Latin American Literature ◽  
Historical Account ◽  
American Novel ◽  
Song Of Solomon ◽  
The Past ◽  
The North ◽  
The Us

This chapter turns from a historical account of the development of the US literature of experience and the Latin American literature of reading to a textual analysis of the US and Latin American historical novel. Hemispheric/inter-American scholars often cite William Faulkner’s Absalom, Absalom! (1936), Gabriel García Márquez’s One Hundred Years of Solitude (1967), and Toni Morrison’s Song of Solomon (1977) as exemplifying instances of literary borrowing across the North–South divide. As I demonstrate, however, each of the later texts also realigns its predecessor’s historical imaginary according to the dominant logics of the US and Latin American literary fields. Whereas the American works foreground experiential models of reconstructing the past and conveying knowledge across generations, García Márquez’s Latin American novel presents reading as the fundamental mode of comprehending and transmitting history.

An Inter-American Episode

2017 ◽  
Author(s):  
Jeffrey Lawrence
Keyword(s):  
Latin America ◽  
Latin American ◽  
Pablo Neruda ◽  
Jose Marti ◽  
The South ◽  
American Reader ◽  
The North ◽  
Literary Theories ◽  
The Us

This chapter focuses on a paradigmatic misencounter between an American experiencer and a Latin American reader. Examining an implicit debate about the sources of Walt Whitman’s poetry and vision of the Americas, I argue that Waldo Frank, one of the twentieth century’s main literary ambassadors from the US to Latin America, positioned Whitman as the representative US writer whose antibookish experiential aesthetics could serve as a model for “American” writers both in the North and in the South. I show how Frank’s framework provided a foil for Borges’s idiosyncratic view that Whitman’s poetry about America derived entirely from his readings of European and US writers. Although much of the best scholarship on Whitman’s reception in Latin America has concentrated on poets like José Martí and Pablo Neruda, who adapted Whitman’s naturalism, I contend that Borges’s iconoclastic portrait of Whitman as a reader profoundly influenced a range of anti-experiential literary theories and practices in Latin America.

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