scholarly journals Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes

2021 ◽  
Vol 126 (2) ◽  
Author(s):  
Jianhua Gong ◽  
Jeffrey J. McGuire
Keyword(s):  
Local Earthquakes ◽  
Converted Phases ◽  
Gorda Plate

EVALUATING SUBDUCTION CONTRIBUTIONS TO THE SOUTHERN CASCADE ARC: INSIGHTS FROM THE GEOCHEMISTRY OF MAFIC ARC LAVAS AND GORDA PLATE SEDIMENTS

2019 ◽  
Author(s):  
Jamie Shaffer ◽  
◽  
Emily R. Johnson ◽  
Meredith A. Cole ◽  
Frank C. Ramos ◽  
...  
Keyword(s):  
Cascade Arc ◽  
Gorda Plate

scholarly journals GPS measurements on pre-, co- and post-seismic surface deformation at first multi-parametric geophysical observatory, Ghuttu in Garhwal Himalaya, India

2020 ◽  
Vol 10 (1) ◽  
pp. 136-144
Author(s):  
P.K. Gautam ◽  
S. Rajesh ◽  
N. Kumar ◽  
C.P. Dabral
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Translational Motion ◽  
Anomalous Behavior ◽  
Deformation Pattern ◽  
Local Earthquakes ◽  
Position Time Series ◽  
Continuous Gps ◽  
Gps Time Series ◽  
Gps Station

Abstract We investigate the surface deformation pattern of GPS station at MPGO Ghuttu (GHUT) to find out the cause of anomalous behavior in the continuous GPS time series. Seven years (2007-2013) of GPS data has been analyzed using GAMIT/GLOBK software and generated the daily position time series. The horizontal translational motion at GHUT is 43.7 ± 1 mm/yr at an angle of 41°± 3° towards NE, while for the IGS station at LHAZ, the motion is 49.4 ±1 mm/yr at 18 ± 2.5° towards NEE. The estimated velocity at GHUT station with respect to IISC is 12 ± 1 mm/yr towards SW. Besides, we have also examined anomalous changes in the time series of GHUT before, after and during the occurrences of local earthquakes by considering the empirical strain radius; such that, a possible relationship between the strain radius and the occurrences of earthquakes have been explored. We considered seven local earthquakes on the basis of Dobrovolsky strain radius condition having magnitude from 4.5 to 5.7, which occurred from 2007 to 2011. Results show irrespective of the station strain radius, pre-seismic surface deformational anomalies are observed roughly 70 to 80 days before the occurrence of a Moderate or higher magnitude events. This has been observed for the cases of those events originated from the Uttarakashi and the Chamoli seismic zones in the Garhwal and Kumaun Himalaya. Occurrences of short (< 100 days) and long (two years) inter-seismic events in the Garhwal region plausibly regulating and diffusing the regional strain accumulation.

Source parameters and focal mechanisms of local earthquakes: Single broadband observatory at ISM Dhanbad

2009 ◽  
Vol 74 (3) ◽  
pp. 413-419 ◽  
Author(s):  
J. R. Kayal ◽  
V. K. Srivastava ◽  
S. N. Bhattacharya ◽  
P. K. Khan ◽  
Rima Chatterjee
Keyword(s):  
Source Parameters ◽  
Focal Mechanisms ◽  
Local Earthquakes

Extension of forward modeling phase-screen code in isotropic and anisotropic media up to critical angle

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. SM107-SM114 ◽  
Author(s):  
James C. White ◽  
Richard W. Hobbs
Keyword(s):  
Critical Angle ◽  
Model Space ◽  
Anisotropic Media ◽  
Forward Modeling ◽  
Phase Screen ◽  
Computationally Efficient ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Phase Corrections ◽  
Converted Phases

The computationally efficient phase-screen forward modeling technique is extended to allow investigation of nonnormal raypaths. The code is developed to accommodate all diffracted and converted phases up to critical angle, building on a geometric construction method. The new approach relies upon prescanning the model space to assess the complexity of each screen. The propagating wavefields are then divided as a function of horizontal wavenumber, and each subset is transformed to the spatial domain separately, carrying with it angular information. This allows both locally accurate 3D phase corrections and Zoeppritz reflection and transmission coefficients to be applied. The phase-screen code is further developed to handle simple anisotropic media. During phase-screen modeling, propagation is undertaken in the wavenumber domain where exact expressions for anisotropic phase velocities are available. Traveltimes and amplitude effects from a range of anisotropic shales are computed and compared with previous published results.

A magnitude scale for local earthquakes in South Australia

1975 ◽  
Vol 65 (5) ◽  
pp. 1267-1285
Author(s):  
Ian C. F. Stewart
Keyword(s):  
Epicentral Distance ◽  
South Australia ◽  
Magnitude Scale ◽  
Source Spectrum ◽  
S Waves ◽  
Scale Parameters ◽  
Local Earthquakes ◽  
Dependent Absorption ◽  
Relationship Of ◽  
The Relationship

Abstract To minimize dispersion in local magnitude estimates due to different instrumental bandwidths, a scale has been established to allow for the average source spectrum, geometrical attenuation, and frequency-dependent absorption. The data used to derive the scale parameters were from S waves recorded in South Australia from 1967 through 1970, in the frequency range 1 to 10 Hz, and for epicentral distances up to 5°. The magnitudes were mainly in the range 1.5 to 3.5. The local scale MN is given by M N = 4.85 + log A g + 0.84 log Δ + 0.0003 f Δ / 2.3 − 2.89 log f + 2.45 ( log f ) 2 + c where Ag mm is the ground amplitude at f Hz at Δ km epicentral distance, and c is a station correction. The dispersion in observations of magnitude has probably been reduced by use of the scale to near the theoretical limits, allowing for possible source radiation patterns. The relationship of the scale to other measures of magnitude is uncertain, but MN may be approximately equivalent to the local Richter magnitude ML for the magnitude range (1.5 &lt; ML &lt; 3.5) commonly observed in South Australia. The scle is limited in use to data in the ranges given above, for local earthquakes in South Australia. Modification is necessary before such a magnitude scale can be applied elsewhere or to different data ranges.

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