Decay rate of p-wave amplitudes from nuclear explosions and the magnitude relations in the epicentral distance range 1° to 98°: a reply to discussion by S. K. Upadhyay

1972 ◽  
Vol 62 (4) ◽  
pp. 1085-1085
Author(s):  
K. L. Kaila
Keyword(s):  
Decay Rate ◽  
Epicentral Distance ◽  
P Wave ◽  
Distance Range ◽  
Nuclear Explosions

Decay rate of P-wave amplitudes from nuclear explosions and the magnitude relations in the epicentral distance range 1° to 98°

1970 ◽  
Vol 60 (2) ◽  
pp. 447-460
Author(s):  
K. L. Kaila
Keyword(s):  
Decay Rate ◽  
Travel Time ◽  
Epicentral Distance ◽  
P Wave ◽  
Amplitude Curve ◽  
Distance Range ◽  
Nuclear Explosions ◽  
The Earth

abstract Study of the decay rate with epicentral distance of P-wave amplitudes from nuclear explosions in the distance range 1° to 98° has revealed that instead of the continuous amplitude curve of Gutenberg, the amplitudes are most appropriately represented by six discontinuous curves. Corresponding to these six amplitude decay curves, magnitude relations were worked out. The new magnitude relations yield consistent magnitudes for nuclear explosions as well as earthquakes independent of epicentral distance over the entire distance range of 1° to 98°. The magnitude values are however slightly shifted towards the higher side by 0.22 magnitude unit (at M = 4.5) as compared to those predicted by the Gutenberg-Richter method. Magnitudes are evaluated for Logan, Blanca and Salmon explosions using the new magnitude relations and they agree fairly well with the published magnitudes for these events determined by other workers using the Gutenberg-Richter method. These amplitude decay curves when compared with the travel-time curves of Carder (1964) do show a reasonable correspondence between the starting points of amplitude curves and the distances where the deeply refracted phases from plausible velocity discontinuities in the mantle start appearing as first arrivals on the surface of the Earth.

P-wave amplitude variation with epicentral distance and the magnitude relations

1975 ◽  
Vol 65 (4) ◽  
pp. 915-926
Author(s):  
K. L. Kaila ◽  
Dipankar Sarkar
Keyword(s):  
Lower Mantle ◽  
Wave Amplitude ◽  
Epicentral Distance ◽  
P Wave ◽  
Amplitude Variation ◽  
Distance Range ◽  
Nuclear Explosions ◽  
The Earth ◽  
Shallow Earthquakes ◽  
Discontinuous Nature

Abstract Investigation of the variation of P-wave amplitudes and d2T/dΔ2 with epicentral distance reveals that the amplitudes in the distance range up to 100° can be represented by seven discontinuous curves. The discontinuous nature of the amplitude curves can be explained due to the possible existence of first- or second-order velocity discontinuities in the upper and lower mantle of the Earth. Seven magnitude relations corresponding to these amplitude curves are given, which yield consistent magnitudes for nuclear explosions as well as for shallow earthquakes.

Duration of nuclear explosion ground motion

1978 ◽  
Vol 68 (4) ◽  
pp. 1133-1145
Author(s):  
Walter W. Hays ◽  
Kenneth W. King ◽  
Robert B. Park
Keyword(s):  
Epicentral Distance ◽  
Ground Motions ◽  
Broad Band ◽  
Time History ◽  
Ground Acceleration ◽  
Ground Shaking ◽  
Distance Range ◽  
Nuclear Explosions ◽  
Dependent Site ◽  
Strong Ground

abstract This paper evaluates the duration of strong ground shaking that results from nuclear explosions and identifies some of the problems associated with its determination. Knowledge of the duration of horizontal ground shaking is important out to epicentral distances of about 44 km and 135 km, the approximate distances at which the ground shaking level falls to 0.01 g for nuclear explosions having yields of about 100 kt and 1,000 kt, respectively. Evaluation of the strong ground motions recorded from the event STRAIT (ML = 5.6) on a linear array of five, broad-band velocity seismographs deployed in the distance range 3.2 to 19.5 km provides information about the characteristics of the duration of ground shaking. The STRAIT data show that: (1) the definition that is used for defining duration is very important; (2) the duration of ground acceleration, as defined in terms of 90 per cent of the integral of the squared time history (Trifunac and Brady, 1975), increased from about 4 to 26 sec over the approximately 20-km distance range; and (3) the duration of ground velocity and displacement were slightly greater because of the effect of the alluvium layer on the propagating surface waves. Data from other events (e.g., MILROW, CANNIKIN, HANDLEY, PURSE) augment the STRAIT data and show that: (1) duration of shaking is increased by frequency-dependent site effects and (2) duration of shaking, as defined by the integral of the squared time history, does not increase as rapidly with increase in yield as is indicated by other definitions of duration that are stated in terms of an amplitude threshold (e.g., bracketed duration, response envelopes). The available data suggest that the duration of ground acceleration, based on the integral definition, varies from about 4 to 40 sec for a 100-kt range explosion and from about 4 to 105 sec for a megaton range explosion in the epicentral distance range of 0 to 44 km and 0 to 135 km, respectively.

Study of low-magnitude seismic events near the Novaya Zemlya nuclear test site

1997 ◽  
Vol 87 (6) ◽  
pp. 1563-1575
Author(s):  
Frode Ringdal
Keyword(s):  
Monitoring Network ◽  
Test Site ◽  
Nuclear Test ◽  
P Wave ◽  
Scaling Effects ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Novaya Zemlya ◽  
Source Scaling ◽  
Low Magnitude

Abstract A study of available seismic data shows that all but one of the 42 known underground nuclear explosions at Novaya Zemlya have been detected and located by stations in the global seismic network. During the past 30 years, only one seismic event in this area has been unambiguously classified as an earthquake (1 August 1986, mb = 4.3). Several other small events, most of which are thought to be either chemical explosions or aftereffects of nuclear explosions, have also been detected. Since 1990, a network of sensitive regional arrays has been installed in northern Europe in preparation for the global seismic monitoring network under a comprehensive nuclear test ban treaty (CTBT). This regional network has provided a detection capability for Novaya Zemlya that is shown to be close to mb = 2.5. Three low-magnitude events have been detected and located during this period, as discussed in this article: 31 December 1992 (mb = 2.7), 13 June 1995 (mb = 3.5), and 13 January 1996 (mb = 2.4). To classify the source types of these events has proved very difficult. Thus, even for the mb = 3.5 event in 1995, we have been unable to provide a confident classification of the source as either an earthquake or explosion using the available discriminants. A study of mb magnitude in different frequency bands shows, as expected, that the calculation of mb at regional distances needs to take into account source-scaling effects at high frequencies. Thus, when comparing a 4 to 8 or 8 to 16 Hz filter band to a “teleseismic” 2 to 4 Hz band, the smaller events have, relatively speaking, significantly more high-frequency energy (up to 0.5 mb units) than the larger events. This suggests that a P-wave spectral magnitude scale might be appropriate. The problem of accurately locating small events using a sparse array network is addressed using the 13 January 1996 event, which was detected by only two arrays, as an illustrative example. Our analysis demonstrates the importance of using accurately calibrated regional travel-time curves and, at the same time, illustrates how array processing can be used to identify an interfering phase from a local disturbance, thereby avoiding location errors due to erroneous phase readings.

Short-period Lg magnitudes: Instrument, attenuation, and source effects

1983 ◽  
Vol 73 (6A) ◽  
pp. 1835-1850
Author(s):  
Robert B. Herrmann ◽  
Andrzej Kijko
Keyword(s):  
United States ◽  
Epicentral Distance ◽  
P Wave ◽  
Magnitude Scale ◽  
Source Effects ◽  
Anelastic Attenuation ◽  
Basic Conclusion ◽  
Short Period ◽  
Central United States ◽  
Definition Of

Abstract The applicaton of the Nutli (1973) definition of the mbLg magnitude to instruments and wave periods other than the short-period WWSSN seismograph is examined. The basic conclusion is that the Nuttli (1973) definition is applicable to a wider range of seismic instruments if the log10(A/T) term is replaced by log10A. For consistency and precision, the notation mbLg should be applied only to magnitudes based upon 1.0 Hz observations. The mbLg magnitude definition was constrained to be consistent with teleseismic P-wave mb estimates from four Central United States earthquakes. In general, for measurements made at a frequency f, the notation mLg(f) should be used, where m L g ( f ) = 2.94 + 0.833 log ⁡ 10 ( r / 10 ) + 0.4342 γ r + log ⁡ 10 A , and r is the epicentral distance in kilometers, γ is the coefficient of anelastic attenuation, and A is the reduced ground amplitude in microns. Given its stability when estimated from different instruments, the mLg(f) magnitude is an optimum choice for an easily applied, standard magnitude scale for use in regional seismic studies.

scholarly journals Triplicated P-wave measurements for waveform tomography of the mantle transition zone

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 339-354 ◽  
Author(s):  
S. C. Stähler ◽  
K. Sigloch ◽  
T. Nissen-Meyer
Keyword(s):  
Transition Zone ◽  
Epicentral Distance ◽  
Body Wave ◽  
Source Parameters ◽  
Body Waves ◽  
P Wave ◽  
Theoretical Modelling ◽  
Finite Frequency ◽  
Mantle Transition Zone ◽  
Band Limited

Abstract. Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical) modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth.

Observations of PKKPab Diffraction Waves Well Beyond Cutoff Distance

2021 ◽  
Author(s):  
Yulin Chen ◽  
Sidao Ni ◽  
Baolong Zhang
Keyword(s):  
Epicentral Distance ◽  
P Wave ◽  
Source Depth ◽  
Large Area ◽  
Core Mantle Boundary ◽  
Velocity Models ◽  
Wave Velocities ◽  
The Earth ◽  
Cutoff Distance ◽  
Lowermost Mantle

Abstract The core mantle boundary (CMB) features the most dramatic contrast in the physical properties within the Earth and plays a fundamental role in the understanding of the dynamic evolution of the Earth’s interior. Seismic core phases such as PKKP sample large area of the lowermost mantle and the uppermost core, thus providing valuable information of the velocity structures on both sides of the CMB. Diffraction Waves Well Beyond Cutoff Distance (PKKPab) is one branch of the triplicated PKKP that can be observed beyond its ray theoretical cutoff distance as a result of diffraction along the CMB. The travel time and slowness of the diffracted PKKPab (denoted as PKKPabdiff) can be used to constrain the P-wave velocities at the lowermost mantle, thus have been investigated in numerous studies. Previous results (Rost and Garnero, 2006) suggest that most of the observations of the PKKPabdiff waves are in the epicentral distance range of 95°–105° (minor arc convention) (PKKPabdiff diffraction length less than 10°). However, high-frequency (∼1 Hz) synthetic seismograms show that the PKKPabdiff waveforms could be observable at distance down to 65°, which indicates that the PKKPabdiff signals could be detected at distances less than 95° in observations. To explore the distance ranges in which PKKPabdiff is observable, we collected global three-component broadband waveforms from 246 events with source depth deeper than 100 km and magnitude above M 6 from 2007 to 2017 available at the Incorporated Research Institutions for Seismology Data Management Center. We analyzed the slowness, polarization, and amplitude of the candidate PKKPabdiff signals, and found 95 events with clear PKKPabdiffsignals, with nearly 60% of the events show PKKPabdiff diffraction lengths greater than 10°, and the longest diffraction distance is beyond 20°. These newly identified PKKPabdiff waves would substantially augment the dataset of core phases for improvements of the CMB velocity models.

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