Source bias in epicenter determinations

1968 ◽  
Vol 58 (6) ◽  
pp. 1791-1796
Author(s):  
Eugene Herrin ◽  
James Taggart
Keyword(s):  
Upper Mantle ◽  
Significant Source ◽  
Volcanic Island ◽  
Constant Delay ◽  
Origin Time ◽  
Station Corrections ◽  
The Pacific ◽  
Tectonically Active ◽  
Using Data ◽  
Consistent Error

ABSTRACT Epicenter determinations using data from stations at distances greater than 20° from the source make use of standard travel times based on a spherically symmetrical Earth. Lateral inhomogeneities in the upper mantle result in relative delays with respect to the standard times. Delays associated with the end of the up-traveling ray can be handled through the use of station corrections. A constant delay beneath the source can not be easily corrected, but it will result only in errors in origin time. However, if the delay arising beneath the source changes with azimuth, a consistent error, here called source bias, will be present in the estimate of the epicenter. Studies of explosions within continental masses have revealed no significant source bias; however, events on two linear, volcanic island chains in the Pacific (Rat Islands-Aleutians and Hawaii) show significant source bias. Errors arising from this effect may be as large as 12 degree and are most likely to occur with events near tectonically active island chains.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

Deterring the development and use of nuclear weapons: a multi-level modeling approach

2017 ◽  
Vol 15 (4) ◽  
pp. 483-493
Author(s):  
Kathleen M Carley ◽  
Geoffrey P Morgan ◽  
Michael J Lanham
Keyword(s):  
Nuclear Weapons ◽  
Dynamic Network ◽  
Pacific Rim ◽  
Country Level ◽  
Dynamic Network Model ◽  
The Pacific ◽  
Stakeholder Model ◽  
Using Data ◽  
Multi Stakeholder ◽  
The Impact

We describe a multi-country, multi-stakeholder model for the accrual and use of nuclear weapons and illustrate the model’s value for addressing nuclear weapon proliferation issues using a historic Pacific Rim scenario. We instantiate the agent-based dynamic network model for information and belief diffusion using data from subject matter experts and data mined from open source news documents. We present the techniques that supported model instantiation. A key feature of this model and these techniques is enabling rapid model re-use through the ability to instantiate at two levels: generically and for specific cases. We demonstrate these generic and specific cases using a scenario regarding North Korea’s interest in nuclear weapons and the resulting impact on the Pacific Rim circa 2014, that is, prior to the fourth and fifth nuclear weapons tests by the Democratic People’s Republic of Korea. A key feature of this model is that it uses two levels of network interaction, the country level and the stakeholder level, thus supporting the inclusion of non-state actors and the assessment of complex scenarios. Using this model, we conducted virtual experiments in which we assessed the impact of alternative courses of action on the overall force posture and desire to develop and use nuclear weapons.

scholarly journals haracterizing the Effects of Two Storms on the Coastal Waters of O‘ahu, Hawai‘i, Using Data from the Pacific Islands Ocean Observing System

Oceanography ◽  
2011 ◽  
Vol 24 (2) ◽  
pp. 182-199 ◽  
Author(s):  
Michael Tomlinson ◽  
Eric De Carlo ◽  
Margaret McManus ◽  
Geno Pawlak ◽  
Grieg Steward ◽  
...  
Keyword(s):  
Coastal Waters ◽  
Pacific Islands ◽  
The Pacific ◽  
Using Data ◽  
Ocean Observing

scholarly journals Amplitudes of surface waves and magnitudes of shallow earthquakes*

1945 ◽  
Vol 35 (1) ◽  
pp. 3-12
Author(s):  
B. Gutenberg
Keyword(s):  
Absorption Coefficient ◽  
Surface Waves ◽  
Epicentral Distance ◽  
Pacific Basin ◽  
Depth Of Focus ◽  
Intermediate Depth ◽  
Station Corrections ◽  
The Pacific ◽  
Shallow Earthquakes

Summary. A study of amplitudes of surface waves having periods of about 20 seconds is employed to improve the calculation of magnitudes of distant shallow earthquakes. Table 3 gives station corrections; table 4, revised figures for the effect of epicentral distance. It is found that for epicentral distances between about 20° and 175° the average observed amplitudes correspond closely to those calculated with an absorption coefficient k = 0.0003 per km. For paths completely outside or inside the Pacific Basin, k = 0.0002± per km., while for paths tangent to its boundary the amplitudes of surface waves with periods of about 20 seconds may be reduced by two-thirds or more (in extreme cases by almost nine-tenths) through reflection or refraction of energy; such seismograms of shallow shocks may be taken as indicating intermediate depth of focus.

scholarly journals Supplemental Material: Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

2020 ◽  
Author(s):  
Vadim Levin ◽  
et al.
Keyword(s):  
Data Analysis ◽  
Costa Rica ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Data Sources ◽  
Mantle Flow ◽  
Analysis Methodology ◽  
The Pacific ◽  
Wave Splitting ◽  
The Caribbean

Data sources, details of data analysis methodology, and additional diagrams and maps of shear wave splitting measurements.<br>

Crustal structure of Pacific Ocean area from dispersion of Rayleigh waves

1963 ◽  
Vol 53 (1) ◽  
pp. 151-165
Author(s):  
Tetsuo A. Santô ◽  
Markus Båth
Keyword(s):  
Pacific Ocean ◽  
Upper Mantle ◽  
Rayleigh Waves ◽  
High Heat ◽  
The Pacific ◽  
New Type ◽  
The Pacific Ocean ◽  
Thin Crust ◽  
Oceanic Structure ◽  
Ridge System

Abstract The dispersion of Rayleigh waves along a great number of Pacific paths has been studied by means of records from Pasadena, California, U. S. A., and Huancayo, Peru. Combining these measurements with previous ones based on records at Tsukuba, Hongkong, Honolulu and Suva, it was found that the central part of the Pacific Ocean exhibits the most oceanic structure, with exception for the Hawaiian Islands. In the south-eastern Pacific Ocean an area could be delineated with a new type of dispersion characteristics, not found in any other part of the Pacific. This area agrees closely with the Easter Island Ridge system, and exhibits unusually thin crust and low upper-mantle velocities as well as exceptionally high heat flow.

Routine location of T-phase sources in the Pacific

1966 ◽  
Vol 56 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Rockne H. Johnson
Keyword(s):  
Peak Power ◽  
Power Level ◽  
Earthquake Magnitude ◽  
Origin Time ◽  
Arrival Times ◽  
Early Results ◽  
The Pacific ◽  
Least Squares Fit ◽  
The Kuril Islands ◽  
T Phase

abstract A program for the routine location of T-phase sources in the Pacific is described. Data for this program are supplied principally by the Pacific Missile Range hydrophone network. Arrival times and power levels are read at Honolulu for processing by an IBM 7040 computer. The solution for location and origin time is the least-squares fit to all hydrophone arrivals which are weighted according to their distribution in azimuth and their distance from the T-phase source. The velocities for the program are obtained from algebraic functions of latitude and longitude which are based upon shot calibrations and upon hydrographic measurements. A T-phase strength is computed from readings of peak power level in a manner analogous to earthquake magnitude. Early results for the r.m.s. difference between T-phase source locations and the corresponding earthquake epicenters were 0.6° in the Aleutians and 1.1° in the Kuril Islands.

scholarly journals Coastal upwelling along the southwest coast of India – ENSO modulation

2008 ◽  
Vol 26 (6) ◽  
pp. 1331-1334 ◽  
Author(s):  
K. Muni Krishna
Keyword(s):  
Coastal Upwelling ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Trade Winds ◽  
Southwest Coast Of India ◽  
Southwest Coast ◽  
Enso Events ◽  
The Pacific ◽  
Basin Scale ◽  
Using Data

Abstract. An index of El Niño Southern Oscillation (ENSO) in the Pacific during pre monsoon season is shown to account for a significant part of the variability of coastal Sea Surface Temperature (SST) anomalies measured a few months later within the wind driven southwest coast of India coastal upwelling region 7° N–14° N. This teleconnection is thought to result from an atmospheric bridge between the Pacific and north Indian Oceans, leading to warm (cold) ENSO events being associated with relaxation (intensification) of the Indian trade winds and of the wind-induced coastal upwelling. This ENSO related modulation of the wind-driven coastal upwelling appears to contribute to the connection observed at the basin-scale between ENSO and SST in the Arabian Sea. The ability to use this teleconnection to give warning of large changes in the southwest coast of India coastal upwelling few months in advance is successfully tested using data from 1998 and 1999 ENSO events.

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