scholarly journals High-frequency source radiation during the 2011 Tohoku-Oki earthquake, Japan, inferred from KiK-net strong-motion seismograms

2013 ◽  
Vol 118 (1) ◽  
pp. 222-239 ◽  
Author(s):  
Hiroyuki Kumagai ◽  
Nelson Pulido ◽  
Eiichi Fukuyama ◽  
Shin Aoi
Keyword(s):  
High Frequency ◽  
Strong Motion ◽  
Source Radiation ◽  
Frequency Source

Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

1987 ◽  
Vol 77 (4) ◽  
pp. 1127-1146
Author(s):  
Giuseppe De Natale ◽  
Raul Madariaga ◽  
Roberto Scarpa ◽  
Aldo Zollo
Keyword(s):  
Frequency Domain ◽  
Stress Drop ◽  
High Frequency ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Source Model ◽  
Parameter Analysis ◽  
Corner Frequency ◽  
Spectral Parameters ◽  
Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

High Frequency Decay Parameter (Kappa) for Ahar–Varzaghan Double Earthquakes, Iran (MW 6.5 & 6.3)

2016 ◽  
Vol 10 (02) ◽  
pp. 1640006 ◽  
Author(s):  
Meghdad Samaei ◽  
Masakatsu Miyajima ◽  
Azad Yazdani ◽  
Farhad Jaafari
Keyword(s):  
High Frequency ◽  
Classical Method ◽  
Strong Motion ◽  
Decay Parameter ◽  
First Line ◽  
Noise Floor ◽  
Strong Motion Records ◽  
Northwestern Iran ◽  
Double Earthquakes ◽  
Automated Procedures

The high frequency decay parameter, kappa and its variations in distance is evaluated using 114 three component strong motion records from two strong events in Northwestern Iran. We show that in classical method of estimating kappa, the results are very sensitive to the choices of [Formula: see text] (where spectrum starts to fall) and [Formula: see text] (where spectrum reaches the noise floor) and automated procedures for estimating kappa are likely to lead to a biased estimation. For the present database, we found an obvious concavity in dependency of kappa on distance. The kappa values in distance were regressed to a trilinear shape for which the first line has a zero slope. Based on this trilinear shape the zero distance kappa are 0.043 and 0.026 for horizontal and vertical components, respectively.

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals Impact of broadband seismology on the understanding of strong motions

1993 ◽  
Vol 83 (3) ◽  
pp. 830-850
Author(s):  
Don Helmberger ◽  
Douglas Dreger ◽  
Richard Stead ◽  
Hiroo Kanamori
Keyword(s):  
High Frequency ◽  
Strong Motion ◽  
Geometrical Spreading ◽  
Low Velocity ◽  
Sierra Madre ◽  
Broadband Seismology ◽  
Whole Space ◽  
Low Velocity Layer ◽  
Lower Crustal ◽  
Velocity Layer

Abstract Most analyses of strong motion attenuation assume simple whole-space type geometrical spreading, namely (1/R) or its modified form e−kR/R. However, broadband data presently becoming available suggests a more complex behavior with substantial crustal effects. Events such as the Sierra Madre event, M = 5.8, triggered the strong motion channels at all of the TERRAscope stations allowing for 0.01-sec sampling of the wavefield. We find that most of the well-defined crustal bodywave arrivals defined and modeled in the 1 to 0.1-hz bandpass also contain high-frequency energy. By comparing the triggered channels with the continuous channels we see that several of the more distant stations triggered on the depth phase sPmP. These phases as well as the depth phase sSmS are obvious in velocity and quite apparent in accelerations. Our best models for Southern California contain a relatively thick low-velocity layer at the surface, roughly 5 km thick with shear velocities below 3 km/sec. This layer or zone, because it appears to vary considerably, controls the wavefield at nearly all frequencies out to about 60 km and yields attenuation decay faster than (1/R). At large ranges the lower crustal triplications dominate and the attenuation curve flattens. Adding random scatters to these layered models adds additional complexity but does not alter the basic flat-layer predictions.

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