scholarly journals Unveiling Tatun volcanic plumbing structure induced by post-collisional extension of Taiwan mountain belt

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hsin-Hua Huang ◽  
E.-S. Wu ◽  
C.-H. Lin ◽  
J. Y.-T. Ko ◽  
M.-H. Shih ◽  
...  
Keyword(s):  
Critical Infrastructure ◽  
Joint Inversion ◽  
Magma Reservoir ◽  
P Wave ◽  
Plumbing System ◽  
Time Data ◽  
Waveform Data ◽  
Tomographic Images ◽  
Travel Time Data ◽  
Volcanic Plumbing System

AbstractThe Tatun Volcanic Group (TVG) is proximal to the metropolis of Taipei City (population of ca. 7 million) and has long been a major concern due to the potential risks from volcanic activity to the population and critical infrastructure. While the TVG has been previously considered a dormant or extinct volcano, recent evidence suggests a much younger age of the last eruption event (~ 6000 years) and possible existence of a magma reservoir beneath the TVG. However, the location, dimension, and detailed geometry of the magma reservoir and plumbing system remains largely unknown. To examine the TVG volcanic plumbing structure in detail, the local P-wave travel time data and the teleseismic waveform data from a new island-wide Formosa Array Project are combined for a 3D tomographic joint inversion. The new model reveals a magma reservoir with a notable P-wave velocity reduction of 19% (ca. ~ 19% melt fraction) at 8–20 km beneath eastern TVG and with possible northward extension to a shallower depth near where active submarine volcanoes that have been detected. Enhanced tomographic images also reveal sporadic magmatic intrusion/underplating in the lower crust of Husehshan Range and northern Taiwan. These findings suggest an active volcanic plumbing system induced by post-collisional extension associated with the collapse of the orogen.

Source mechanism of the Truckee, California, earthquake of September 12 1966

1970 ◽  
Vol 60 (4) ◽  
pp. 1199-1208 ◽  
Author(s):  
Yi-Ben Tsai ◽  
Keiiti Aki
Keyword(s):  
Seismic Moment ◽  
Additional Data ◽  
Focal Depth ◽  
P Wave ◽  
Eastern United States ◽  
Time Data ◽  
Travel Time Data ◽  
Amplitude Spectra ◽  
Plane Solution ◽  
Minimum Estimate

abstract With additional data on P wave polarities, the existing fault plane solution for the Truckee, California, earthquake of September 12 1966 (Ryall, Van Wormer and Jones, 1968) is revised to have the following strike and dip angles for its nodal planes: Strike Dip Plane A N 44°E 80°SE Plane B N 134°E 90° Nodal plane A is shown to agree very well with the aftershock zone determined by Greensfelder (1968). The observed Rayleigh and Love wave amplitude spectra from four WWSSN stations in the eastern United States are consistent with the revised solution, but not with the original one by Ryall et al. From these data, the focal depth and seismic moment of the earthquake are determined as 10 km and 0.83 × 1025 dyne-cm, respectively. The focal depth so obtained is the same as that determined from the near station travel time data by Ryall et al. The seismic moment is used to give a minimum estimate of about 30 cm for the average dislocation of the fault.

Travel times from central Pacific nuclear explosions and inferred mantle structure

1964 ◽  
Vol 54 (6B) ◽  
pp. 2271-2294
Author(s):  
Dean S. Carder
Keyword(s):  
Single Point ◽  
P Wave ◽  
Graphical Form ◽  
Travel Times ◽  
Time Data ◽  
Central Pacific ◽  
Arrival Times ◽  
Nuclear Explosions ◽  
Straight Line ◽  
Travel Time Data

Abstract Travel time data, from widely recorded nuclear detonations in the Eniwetok and Bikini atolls of the central Pacific, have been compiled and are presented. Although a number of stations recorded ten or more events from each atoll, the resulting data may be considered as from a single point source, precisely known in time and place. Composite P-wave travel times are presented in a graphical form and, in the distance range from 3 to 102 degrees, are represented as eight near straight-line segments. P-wave speeds in the top of the mantle average about 8.2 km/sec to distances beyond 17 degrees, and a sharp discontinuity at 19.5 degrees is indicated. There is no evidence for or against a low-speed layer in the upper mantle nor for a regional shadow zone. A mantle model consisting of a number of discrete spherical shells has been constructed. A core depth of 2,870 km, 30 km short of the accepted value, is calculated from PcP arrival times at Matsushiro and College, which are 2.5 and 3.5 sec. earlier than are indicated in the Jeffreys-Bullen tables.

scholarly journals Shear waves through the Earth's core

1935 ◽  
Vol 149 (866) ◽  
pp. 88-103 ◽  
Keyword(s):  
Magnetic Properties ◽  
P Wave ◽  
Time Data ◽  
P Waves ◽  
Nickel Iron ◽  
S Waves ◽  
The Core ◽  
The Earth ◽  
Travel Time Data ◽  
Core Depth

Seismological evidence of a central core to the earth was first pointed out by Oldham in 1906. From his analysis of travel-time data regarding longitudinal (P) and transverse (S) waves observed at great distances from earthquake epicentres, he concluded that at a depth equal to about three-fifths of the radius there occurs a transition to material possessing radically different physical properties from that external to this boundary. With the aid of more extensive data assembled by Turner and others, the problem was later re-examined independently by Knott and by Gutenberg. The latte concluded that at a depth of 2900 km the velocity of P waves suddenly decreases from over 13 km per sec to about 8 1/2. The theory involves the appearance of a delayed P wave at epicentral distances beyond 143º, and the chief characteristics predicted for this wave have been amply verified by Gutenberg, by Macelwane and by Lehmann. Also Wadati has lately confirmed the earlier estimates of the core depth from observation on S c S. Mean density considerations suggest that this core is metallic; and the magnetic properties of the earth are consistent with a nickel-iron composition resembling that found in many meteors.

scholarly journals Three dimensional velocity structure and relocated aftershocks for the 1985 Constantine, Algeria (MS = 5.9) earthquake

1998 ◽  
Vol 41 (1) ◽  
Author(s):  
M. ou A. Bounif ◽  
C. Dorbath
Keyword(s):  
Velocity Structure ◽  
Three Dimensional ◽  
Velocity Model ◽  
P Wave ◽  
Time Data ◽  
Data Set ◽  
S Waves ◽  
Travel Time Data ◽  
Velocity Image ◽  
Local Earthquake

Local earthquake travel-time data were inverted to obtain a three dimensional tomographic image of the region centered on the 1985 Constantine earthquake. The resulting velocity model was then used to relocate the events. The tomographic data set consisted of P and S waves travel-times from 653 carefully selected aftershocks of this moderate size earthquake, recorded at 10 temporary stations. A three-dimensional P-wave velocity image to a depth of 12 km was obtained by Thurber's method. At shallower depth, the velocity contrasts reflected the differences in tectonic units. Velocities lower than 4 km/s corresponded to recent deposits, velocities higher than 5 km/s to the Constantine Neritic and the Tellian nappes. The relocation of the aftershocks indicates that most of the seismicity occured where the velocity exceeded 5.5 km/s. The aftershock distribution accurately defined the three segments involved in the main shock and led to a better understanding of the rupture process.

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