Moho dip and crustal anisotropy in northwestern Nevada from teleseismic receiver functions

1997 ◽  
Vol 87 (3) ◽  
pp. 745-754
Author(s):  
Xiaohua Peng ◽  
Eugene D. Humphreys
Keyword(s):  
Velocity Model ◽  
Receiver Functions ◽  
Good Evidence ◽  
South American ◽  
Crustal Anisotropy ◽  
The North ◽  
Seismic Experiment ◽  
Northerly Direction ◽  
Southern Central ◽  
Northwestern Nevada

Abstract Receiver functions are derived from teleseismic waves recorded during the 1988 to 1989 PASSCAL Basin and Range passive-source seismic experiment in northwestern Nevada. A velocity model involving both a planar dipping Moho and crustal anisotropy is needed to explain the radial and tangential motions of the observed PS conversions. An arrival-time difference often observed between radial and tangential Moho PS conversions suggests an anisotropic crust. The PS conversions are large and indicate a major discontinuity under the area. The particle motion directions for most of the tangential components change sign between South American events and events from the other two source areas (Japan and Tonga regions), providing good evidence for a Moho dipping approximately to the north. Also, the PS conversions from the Moho follow direct P arrivals by about 3.2 sec under the southern part of the array, 3.4 sec under the southern central part of the array, and 3.7 sec under the northern part of the array, indicating a Moho that varies in depth from about 26 to 31 km. A velocity model with the Moho dipping ∼9° in a nearly northerly direction and an anisotropic crust with a split time of ∼0.25 sec and a fast axis of ∼130° best explain these observations.

Geodynamic study of the north of the Andes block (Colombia, Panama, Ecuador and Venezuela) through gnss-gps: models of displacements, models of deformation and definition of local and regional geodynamic structures.

2020 ◽  
Author(s):  
Berrocoso Manuel ◽  
Del Valle Arroyo Pablo Emilio ◽  
Colorado Jaramillo David Julián ◽  
Gárate Jorge ◽  
Fernández-Ros Alberto ◽  
...  
Keyword(s):  
South America ◽  
Seismic Activity ◽  
Great Part ◽  
Velocity Model ◽  
South American ◽  
The South ◽  
South American Plate ◽  
Northern Andes ◽  
Velocity Models ◽  
The North

<p>The northwest of South America is conformed by the territories of Ecuador, Colombia and Venezuela. Great part of these territories make up the Northern Andes Block (BAN). The tectonic and volcanic activity in the northwest of South America is directly related to the interaction of the South American plate, and the Nazca and Caribbean plates, with the Maracaibo and Panama-Chocó micro plates. The high seismic activity and the high magnitude of the recorded earthquakes make any study necessary to define this complex geodynamic region more precisely. This work presents the velocity models obtained through GNSS-GPS observations obtained in public continuous monitoring stations in the region. The observations of the Magna-eco network (Agustín Codazzi Geographic Institute) are integrated with models already obtained by other authors from the observations of the GEORED network (Colombian Geological Service). The observations have been processed using Bernese software v.52 using the PPP technique; obtaining topocentric time series. To obtain the speeds, a process of filtering and adjustment of the topocentric series has been carried out. Based on this velocity model, regional structures have been defined within the Northern Andes Block through a differentiation process based on the corresponding speeds of the South American, Nazca and Caribbean tectonic plates. Local geodynamic structures within the BAN itself have been established through cluster analysis based on both the direction and the magnitude of each of the vectors obtained. Finally, these structures have been correlated with the most significant geodynamic elements (fractures, faults, subduction processes, etc.) and with the associated seismic activity.</p>

Distribution of crustal azimuthalanisotropy beneath the North China Craton: Insights from analysis of receiver functions

2020 ◽  
Author(s):  
Tuo Zheng ◽  
S. Stephen Gao ◽  
Zhifeng Ding ◽  
Xiaoping Fan
Keyword(s):  
Fault Zone ◽  
North China Craton ◽  
North China ◽  
Receiver Functions ◽  
Azimuthal Anisotropy ◽  
Crustal Anisotropy ◽  
Near Surface ◽  
The North ◽  
Upper Mantle Anisotropy ◽  
Lithospheric Extension

<p>To characterize crustal anisotropy beneath the North China Craton (NCC), we apply a recently developed deconvolution approach to effectively remove near-surface reverberations in the receiver functions recorded at 200 broadband seismic stations and subsequently determine the fast orientation and the magnitude of crustal azimuthal anisotropy by fitting the sinusoidal moveout of the P to S converted phases from the Moho and intracrustal discontinuities. The magnitude of crustal anisotropy is found to range from 0.06 s to 0.54 s, with an average of 0.25 ± 0.08 s. Fault-parallel anisotropy in the seismically active Zhangjiakou-Penglai Fault Zone is significant and could be related to fluid-filled fractures. Historical strong earthquakes mainly occurred in the fault zone segments with significant crustal anisotropy, suggesting that the measured crustal anisotropy is closely related to the degree of crustal deformation. The observed spatial distribution of crustal anisotropy suggests that the northwestern terminus of the fault zone probably ends at about 114°E. Also observed is a sharp contrast in the fast orientations between the western and eastern Yanshan Uplifts separated by the North-South Gravity Lineament. The NW-SE trending anisotropy in the western Yanshan Uplift is attributable to “fossil” crustal anisotropy due to lithospheric extension of the NCC, while extensional fluid-saturated microcracks induced by regional compressive stress are responsible for the observed ENE-WSW trending anisotropy in the eastern Yanshan Uplift. Comparison of crustal anisotropy measurements and previously determined upper mantle anisotropy implies that the degree of crust-mantle coupling in the NCC varies spatially.</p>

Diversification of the North American Doellingeria-Eucephalus Clade (Astereae: Asteraceae) Inferred from Molecular and Morphological Evidence

2019 ◽  
Vol 44 (4) ◽  
pp. 930-942
Author(s):  
Geraldine A. Allen ◽  
Luc Brouillet ◽  
John C. Semple ◽  
Heidi J. Guest ◽  
Robert Underhill
Keyword(s):  
North American ◽  
Sequence Data ◽  
Phylogenetic Analyses ◽  
Sister Group ◽  
Morphological Evidence ◽  
South American ◽  
New Combinations ◽  
The North ◽  
Hybridization Event ◽  
Ancient Hybridization

Abstract—Doellingeria and Eucephalus form the earliest-diverging clade of the North American Astereae lineage. Phylogenetic analyses of both nuclear and plastid sequence data show that the Doellingeria-Eucephalus clade consists of two main subclades that differ from current circumscriptions of the two genera. Doellingeria is the sister group to E. elegans, and the Doellingeria + E. elegans subclade in turn is sister to the subclade containing all remaining species of Eucephalus. In the plastid phylogeny, the two subclades are deeply divergent, a pattern that is consistent with an ancient hybridization event involving ancestral species of the Doellingeria-Eucephalus clade and an ancestral taxon of a related North American or South American group. Divergence of the two Doellingeria-Eucephalus subclades may have occurred in association with northward migration from South American ancestors. We combine these two genera under the older of the two names, Doellingeria, and propose 12 new combinations (10 species and two varieties) for all species of Eucephalus.

RESOLVING SOURCE-TO-SINK DYNAMICS BY MULTI-PROXY DATA FROM THE NORTH AND SOUTH AMERICAN CONTINENTAL SEDIMENTARY ARCHIVES

2020 ◽  
Author(s):  
Barbara Carrapa ◽  
◽  
Andrea Stevens Goddard ◽  
Scott Meek ◽  
Peter G. DeCelles
Keyword(s):  
South American ◽  
Proxy Data ◽  
The North ◽  
Source To Sink ◽  
North And South

The 25 October, 2018 Zakynthos (Greece) earthquake: seismic activity at the transition between a transform fault and a subduction zone.

2020 ◽  
Author(s):  
P Papadimitriou ◽  
V Kapetanidis ◽  
A Karakonstantis ◽  
I Spingos ◽  
K Pavlou ◽  
...  
Keyword(s):  
Spatial Clustering ◽  
Accretionary Prism ◽  
Velocity Model ◽  
Strike Slip ◽  
Double Difference ◽  
Strain Partitioning ◽  
Transform Fault ◽  
Fault Plane Solutions ◽  
The North ◽  
Waveform Modelling

Summary The properties of the Mw = 6.7 earthquake that took place on 25 October 2018, 22:54:51 UTC, ∼50 km SW of the Zakynthos Island, Greece, are thoroughly examined. The main rupture occurred on a dextral strike-slip, low-angle, east-dipping fault at a depth of 12 km, as determined by teleseismic waveform modelling. Over 4000 aftershocks were manually analysed for a period of 158 days. The events were initially located with an optimal 1D velocity model and then relocated with the double-difference method to reveal details of their spatial distribution. The latter spreads in an area spanning 80 km NNW-SSE and ∼55 km WSW-ENE. Certain parts of the aftershock zone present strong spatial clustering, mainly to the north, close to Zakynthos Island, and at the southernmost edge of the sequence. Focal mechanisms were determined for 61 significant aftershocks using regional waveform modelling. The results revealed characteristics similar to the mainshock, with few aftershocks exhibiting strike-slip faulting at steeper dip angles, possibly related to splay faults on the accretionary prism. The slip vectors that correspond to the east-dipping planes are compatible with the long-term plate convergence and with the direction of coseismic displacement on the Zakynthos Island. Fault-plane solutions in the broader study area were inverted for the determination of the regional stress-field. The results revealed a nearly horizontal, SW-NE to E-W-trending S1 and a more variable S3 axis, favouring transpressional tectonics. Spatial clusters at the northern and southern ends of the aftershock zone coincide with the SW extension of sub-vertical along-dip faults of the segmented subducting slab. The mainshock occurred in an area where strike-slip tectonics, related to the Cephalonia Transform Fault and the NW Peloponnese region, gradually converts into reverse faulting at the western edge of the Hellenic subduction. Plausible scenarios for the 2018 Zakynthos earthquake sequence include a rupture on the subduction interface, provided the slab is tilted eastwards in that area, or the reactivation of an older east-dipping thrust as a low-angle strike-slip fault that contributes to strain partitioning.

Paleomagnetism of the Clam Bank Formation and paleolatitude estimates for western Newfoundland

1993 ◽  
Vol 30 (4) ◽  
pp. 776-786
Author(s):  
G. Murthy ◽  
R. Pätzold
Keyword(s):  
North American ◽  
Early Paleozoic ◽  
The North ◽  
Northerly Direction ◽  
Deformation Event ◽  
Recent Origin ◽  
Component C ◽  
Acadian Orogeny ◽  
North American Craton ◽  
Devonian Age

The Pridolian Clam Bank Formation around Lourdes Cove on the Port au Port Peninsula, western Newfoundland, underwent deformation during the Acadian orogeny. As a result, some of the beds were overturned, but the stratification planes can be accurately determined everywhere. Paleomagnetic studies of the Clam Bank Formation have yielded three well-defined components of magnetization, all acquired subsequent to the deformation event: component A with D = 337.3°, I = −28.3°, (N = 16 sites, k = 25.3, α95 = 7.5°), with a corresponding paleopole at 23.2°N, 145.0°E (dp, dm = 4.5°, 8.2°); component B with D = 172.9°, I = 5.7° (N = 35 specimens, k = 10.2, α95 = 6.4°), with a corresponding paleopole at 38.2°N, 130.1°E (dp, dm = 3.2°, 6.4°); component C with D = 350.4°, I = 69.8° (N = 33 specimens, k = 8.9, α95 = 8.9°). A pre-Mesozoic origin of the A and B components is indicated by the presence of normal and reversed components in specific sites; by the lack of correspondence between the A and B paleopoles and the Mesozoic and later pole positions from the Appalachians and the North American craton; and by agreement with Paleozoic poles from the region. The A component was probably acquired immediately after deformation during the Acadian orogeny. The B component is probably a chemical remanence that was acquired during Permo-Carboniferous (Kiaman) time. The C component is of recent origin, probably acquired in the present Earth's field. Paleomagnetic data from western Newfoundland are used in a localized setting to construct a paleopole sequence and to estimate paleolatitudes for western Newfoundland during the Paleozoic. Keeping in mind the paucity of data for Siluro-Devonian age from this region, western Newfoundland seems to have been at its southernmost position at the end of the Ordovician and to have occupied equatorial latitudes during the Permo-Carboniferous. The paleolatitude trend suggests that this block, which is part of the North American craton, moved in a southerly direction during the early Paleozoic and in a northerly direction during the middle and late Paleozoic.

scholarly journals Regionally extinct species rediscovered: the bush dog Speothos venaticus in Minas Gerais, south-eastern Brazil

Oryx ◽  
2014 ◽  
Vol 49 (1) ◽  
pp. 60-63 ◽  
Author(s):  
Guilherme Braga Ferreira ◽  
Marcelo Juliano Rabelo Oliveira ◽  
Rogério Cunha de Paula ◽  
Flávio Henrique Guimarães Rodrigues ◽  
Érica Daniele Cunha Carmo
Keyword(s):  
Protected Areas ◽  
Minas Gerais ◽  
The State ◽  
South American ◽  
North West ◽  
South Eastern ◽  
The North ◽  
Eastern Brazil ◽  
Bush Dog ◽  
Speothos Venaticus

AbstractThe bush dog Speothos venaticus, a rare Near Threatened South American canid that lives in packs, was thought to be extinct in Minas Gerais state, south-eastern Brazil, until recently. Here, we report four recent records of the species in Minas Gerais, the first in the state since the description of the species in 1842. All records are from the Cerrado ecosystem in the north and north-west of the state; two are from animals found dead, one from footprints and another from a camera trap. Three of the records were inside or close (< 10 km) to strict protected areas, in a region recognized as the Protected Areas Mosaic Sertão Veredas–Peruaçu, where we expect any new records of the bush dog to be found. We discuss the low probability of detecting the bush dog and the main regional threats to the species, and emphasize the need to protect large and interconnected natural areas and keep them free of domestic dogs to avoid the extinction of the bush dog in Minas Gerais.

scholarly journals Human Impacts on Estuarine Erosion-Deposition in Southern Central Vietnam: Observation and Hydrodynamic Simulation

2021 ◽  
Vol 13 (15) ◽  
pp. 8303
Author(s):  
Vu Tuan Anh ◽  
Pham Ba Trung ◽  
Kim-Anh Nguyen ◽  
Yuei-An Liou ◽  
Minh-Thu Phan
Keyword(s):  
Deposition Process ◽  
Southwest Monsoon ◽  
North Coast ◽  
Northeast Monsoon ◽  
Southern Coast ◽  
Erosion Processes ◽  
The North ◽  
Central Vietnam ◽  
Southern Central ◽  
Deposition Processes

This paper aims to identify the causes and sources of erosion and deposition at small estuaries in southern central Vietnam under human intervention. The jetty built at the Tam Quan river mouth (Binh Dinh Province, Vietnam) serves as the base for the study. After its completion at the end of 2009, the hydrodynamic and erosion-deposition processes in the region have been significantly altered. Inside the estuary, the waves are not influenced, but the currents are increased during the ebb tide period and decreased during the flood tide timeframe. During the southwest monsoon, the jetty could cause an increase in the deposition process in both frequency and area, whereas the erosion process tends to narrow the area and increase the frequency on the north coast. In contrast, both deposition and erosion processes are increased on the southern coast. About 5859 m3 of sediments are deposited in the channel gate mainly by local sources. During the northeast monsoon, both deposition and erosion processes are located over a narrow area with frequency increased on the north coast, whereas the deposition process is narrowed with higher frequency on the southern coast. The total amount of sediment deposited at the estuary is 56,446 m3, of which 74.2% is from the onsite erosion material, 15.8% from the river and 10% from the longshore transportation. Generally, due to mainly erosion-deposition processes, sediment volume is accumulated during the northeast monsoon with amount 9.6 times more than that the southwest monsoon. The erosion-deposition processes are contributed to by poor practical management and local human activities inland and in the coastal regions, as well as the natural situation, resulting in serious impacts on society, the economy and the environment. Hence, the governance of the erosion-deposition processes and sediment load in small estuaries appear to contribute to the master plan for the local sustainable development of society and the economy.

Sediment Thickness and Moho Depth Beneath Western Indonesian Region From Teleseismic Receiver Function

2021 ◽  
Author(s):  
Syaiful Bahri ◽  
Wiwit Suryanto ◽  
Drajat Ngadmanto
Keyword(s):  
Shear Wave ◽  
Shear Wave Velocity ◽  
Receiver Function ◽  
Velocity Model ◽  
Moho Depth ◽  
Sediment Layer ◽  
The North ◽  
East Kalimantan ◽  
Crust Layer ◽  
Teleseismic Receiver Function

Abstract The Earth's crust layer and sediment in Western Indonesia has been studied using the inversion of teleseismic receiver function from BMKG’s seismic network. Earthquake events were analyzed in this study with a moment magnitude greater than 6.0 with epicentral distances of 30° to 90°. A total of 60 earthquake events were observed and recorded by 91 stations around the study area. Furthermore, an inversion process was carried out using the initial velocity model from the modification of the AK135f velocity model to obtain the shear wave velocity structure below each stations. The velocity model from the azimuthally stacked vertical receiver function showed that the sediment layer had a relatively medium shear wave velocity value with an average of 2.1 km/s, while the crust layer had 4.60 km/s. The sedimentary layer thickness in this region also varies between 2 km to 10 km. A relatively thick sediment layer of about 8 km to 10 km was observed in two locations, in East Kalimantan associated with the Kutai Basin and Northern part of Sumatera in the North Sumatera Basin, a two major oil producer basinal area in Indonesia. The Moho discontinuity was also found at depths that vary between 16 km to 50 km. In addition, the most shallow Moho depth is 16 km below the North Kalimantan and North part of West Java, while the deeper Moho depth of 50 km is located below East Kalimantan, Central Kalimantan, North Sumatera and South Sumatera.

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