Seismic detection of the low-velocity anomaly at the crust and uppermost mantle beneath the central Tien Shan

2020 ◽  
Author(s):  
Ran Cui ◽  
Yuanze Zhou
Keyword(s):  
Tarim Basin ◽  
Velocity Structure ◽  
Orogenic Belt ◽  
Tien Shan ◽  
P Wave ◽  
Uppermost Mantle ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
Short Period ◽  
Seismic Detection

<p>As one of the most active intracontinental orogenic belts in the world, the Tien Shan orogenic belt originated in the Paleozoic and then experienced tectonic activities such as plate subduction and closure of the Paleo-Asian Ocean. Previous seismological and geodynamic studies have shown the observed the low-velocity anomaly (LVA) beneath the central Tien Shan at the uppermost mantle, which has a significant influence on the formation and modification of the crust and mantle lithosphere ( Lei et al, 2007). However, the distribution, morphology and physical property of the LVA are highly debatable.</p><p>We conduct 2-D forward waveform modeling based on spectral-element method (SEM) to investigate waveform distortions that were generated by the velocity contrast boundary of the LAV. The broadband P- and S- waves from three intermediate-depth earthquakes at Hindu Kush-Pamir were recorded by the Chinese Digital Seismograph Network (Zheng et al., 2010). We use these records to confirm the location, shape and velocity decrement of the LVA by fitting the observed records with the synthetics through SEM based on the 1D velocity structures (TSTB-B) of the central Tien Shan and northern Tarim basin (Gao et al., 2017). We find the LVA at 10~100 km beneath the eastern part of the central Tien Shan. And the northward under-thrusting of the Tarim Basin may trigger some mantle upwelling, contributing to the observed LVA.</p><p>Lei, J., Zhao, D. (2007). Teleseismic P-wave tomography and the upper mantle structure of the central Tien Shan orogenic belt.<em> Physics of the Earth and Planetary Interiors</em>, 162, 165-185, doi: 10.1016/j.pepi.200704010.</p><p>Zheng, X., Jiao, W., Zhang, C., et al. (2010). Short-Period Rayleigh-Wave Group Velocity Tomography through Ambient Noise Cross-Correlation in Xinjiang, Northwest China.<em> Bulletin of the Seismological Society of America</em>, 100(3): 1350-1355, doi: 10.1785/0120090225.</p><p>Gao, Y., Cui, Q., Zhou, Y. (2017). Seismic detection of P-wave velocity structure atop MTZ beneath the Central Tian Shan and Tarim Basin. <em>Chinese Journal of Geophysics ( in Chinese with English Abstract )</em>, 60 (1) : 98-111, doi: 10.6038 /cjg20170109.</p>

scholarly journals Crustal velocity structure of the Apennines (Italy) from P-wave travel time tomography

1996 ◽  
Vol 39 (6) ◽  
Author(s):  
C. Chiarabba ◽  
A. Amato
Keyword(s):  
Velocity Structure ◽  
P Wave ◽  
Depth Interval ◽  
Low Velocity ◽  
Data Set ◽  
Arrival Times ◽  
Velocity Anomaly ◽  
Minimum Number ◽  
Velocity Images ◽  
Lower Crustal

In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy), focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data) we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km) in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

SEISMIC DETECTION OF A LOW-VELOCITY ANOMALY UNDER THE STAGNANT SLAB BENEATH THE EASTERN NORTH CHINA CRATON WITH THE P-WAVE TRIPLICATION

2016 ◽  
Vol 59 (3) ◽  
pp. 276-287
Author(s):  
CUI Hui-Hui ◽  
ZHOU Yuan-Ze ◽  
SHI Yao-Lin ◽  
WANG Xiao-Ran ◽  
LI Guo-Hui
Keyword(s):  
North China Craton ◽  
North China ◽  
P Wave ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
Seismic Detection ◽  
Stagnant Slab

P-wave velocity structure of the Earth's crust beneath Vancouver Island

1983 ◽  
Vol 20 (5) ◽  
pp. 742-752 ◽  
Author(s):  
George A. McMechan ◽  
George D. Spence
Keyword(s):  
Velocity Structure ◽  
General Structure ◽  
Vertical Component ◽  
Vancouver Island ◽  
P Wave ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
P Wave Velocity ◽  
Refraction Data ◽  
Velocity Zone

Refraction data were recorded from three shot points out to a maximum distance of ~330 km as part of the 1980 Vancouver Island Seismic Project (VISP80). These vertical component data are partially reversed and so can be interpreted in terms of two-dimensional structures by iterative modeling of P-wave travel times and amplitudes. The structure of the upper crust is the best constrained part of the model. It consists, generally, of a gradually increasing velocity from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth, where the velocity increases sharply to ~7 km/s. Below ~20 km depth, the model becomes speculative because the data provide only indirect constraints on velocities at these depths. An interpretation that fits the observed times and amplitudes has a low velocity zone in the lower crust and a Moho at 37 km depth. The only significant departure from this general structure is beneath the central part of Vancouver Island where the 15.5 km boundary in the model attains a depth of ~23 km, below which there appears to be a local high velocity anomaly.

scholarly journals Tomographic image of the crust and uppermost mantle of the Ionian and Aegean regions

1997 ◽  
Vol 40 (1) ◽  
Author(s):  
B. Alessandrini ◽  
L. Beranzoli ◽  
G. Drakatos ◽  
C. Falcone ◽  
G. Karantonis ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Mediterranean Area ◽  
P Wave ◽  
Moho Depth ◽  
Uppermost Mantle ◽  
Low Velocity ◽  
Central Mediterranean ◽  
Data Set ◽  
Velocity Anomaly ◽  
P Wave Velocity

We present a tomographic view of the crust and uppermost mantle beneath the Central Mediterranean area obtained from P-wave arrival times of regional earthquakes selected from the ISC bulletin. The P-wave velocity anomalies are obtained using Thurber's algorithm that jointly relocates earthquakes and computes velocity adjustments with respect to a starting model. A specific algorithm has been applied to achieve a distribution of epicentres as even as possible. A data set of 1009 events and 49072 Pg and Pn phases was selected. We find a low velocity belt in the crust, evident in the map view at 25 km of depth, beneath the Hellenic arc. A low velocity anomaly extends at 40 km of depth under the Aegean back arc basin. High velocities are present at Moho depth beneath the Ionian sea close to the Calabrian and Aegean arcs. The tomographic images suggest a close relationship between P-wave velocity pattern and the subduction systems of the studied area.

Delineation of a low‐velocity body under the Roosevelt Hot Springs geothermal area, Utah, using teleseismic P‐wave data

Geophysics ◽  
1981 ◽  
Vol 46 (10) ◽  
pp. 1456-1466 ◽  
Author(s):  
Russell Robinson ◽  
H. M. Iyer
Keyword(s):  
Hot Springs ◽  
Velocity Structure ◽  
P Wave ◽  
Wave Form ◽  
Geothermal Area ◽  
Uppermost Mantle ◽  
Low Velocity ◽  
Near Surface ◽  
High Attenuation ◽  
Partial Melt

To assess the nature of the heat source associated with the Roosevelt Hot Springs geothermal area, we have investigated the P‐wave velocity structure of the crust and uppermost mantle in the vicinity of the Mineral Mountains, southwest Utah, a region of late Cenozoic rhyolitic and basaltic volcanic activity. A roughly square (30 × 30 km) array of 15 seismographs, centered on the mountains, was operated for a period of 46 days, during which 72 teleseismic events were recorded with sufficient quality for calculation of P‐wave traveltime residuals. Relative residuals, using the array average for each event as reference, show a clear pattern of azimuthal variation of up to 0.3 sec. This pattern implies the existence of a localized region of relatively low‐velocity material extending up from the upper mantle to depths of about 5 km under the Mineral Mountains. A three‐dimensional (3-D) inversion of the data confirms this conclusion and yields a model featuring a region of low velocity (5 to 7 percent less than the surrounding rock) centered under the geothermal area and extending from about 5-km depth down into the uppermost mantle. The near‐surface velocities obtained in the inversion clearly reveal the structure of the region, part of the Basin and Range province. An azimuthally changing pattern of wave‐form distortion, restricted to the central Mineral Mountains, indicates the presence of a small but intensely anomalous region of low velocity and high attenuation at depths of about 15 km. Although we cannot rule out an explanation for the low velocity purely in terms of compositional changes, in view of the geothermal and volcanic manifestations found in the region we prefer an explanation in terms of abnormally high temperature and a small fraction of partial melt. A partial melt model implies a much greater heat reservoir than does a model involving only circulation along deep fault zones.

Three-dimensional seismic structure of the lithosphere under Montana Lasa

1976 ◽  
Vol 66 (2) ◽  
pp. 501-524
Author(s):  
Keiiti Aki ◽  
Anders Christoffersson ◽  
Eystein S. Husebye
Keyword(s):  
Generalized Inverse ◽  
Random Medium ◽  
Three Dimensional ◽  
P Wave ◽  
Seismic Structure ◽  
Low Velocity ◽  
Medium Theory ◽  
Velocity Anomaly ◽  
Inversion Techniques ◽  
Teleseismic Events

abstract Using P-wave residuals for teleseismic events observed at the Montana Large Aperture Seismic Array (LASA), we have determined the three-dimensional seismic structure of the lithosphere under the array to a depth of 140 km. The root-mean-square velocity fluctuation was found to be at least 3.2 per cent which may be compared to estimate of ca. 2 per cent based on the Chernov random medium theory. The solutions are given by both the generalized inverse and stochastic inverse methods in order to demonstrate the relative merit of different inversion techniques. The most conspicuous feature of the lithosphere under LASA is a low-velocity anomaly in the central and northeast part of the array siting area with the N60°E trend and persisting from the upper crust to depths greater than 100 km. We interpret this low-velocity anomaly as a zone of weakness caused by faulting and shearing associated with the building of the Rocky Mountains.

scholarly journals P-wave crustal tomography of Greece with use of an accurate two-point ray tracer

1997 ◽  
Vol 40 (1) ◽  
Author(s):  
G. Drakatos ◽  
G. Karantonis ◽  
G. N. Stavrakakis
Keyword(s):  
Large Scale ◽  
Velocity Structure ◽  
Three Dimensional ◽  
Seismic Energy ◽  
Aegean Sea ◽  
P Wave ◽  
Low Velocity ◽  
Aegean Area ◽  
Arrival Times ◽  
Horizontal Variations

The three-dimensional velocity structure of the crust in the Aegean sea and the surrounding regions (34.0º-42.OºN, 19.0ºE-29.0ºE) is investigated by inversion of about 10000 residuals of arrival times of P-wave from local events. The resulting velocity structure shows strong horizontal variations due to the complicated crustal structure and the variations of crustal thickness. The northern part of the region generally shows high velocities. In the inner part of the volcanic arc (Southern Aegean area), relatively low velocities are observed, suggesting a large-scale absorption of seismic energy as confirmed by the low seismicity of the region. A low velocity zone was observed along the subduction zone of the region, up to a depth of 4 km. The existence of such a zone could be due to granitic or other intrusions in the crust during the uplift of the region during Alpidic orogenesis.

Sign in / Sign up

Export Citation Format

Share Document