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- Dineva, Savka
(författare)
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Eastern Section 2008 meeting
- 2009
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Ingår i: Seismological Research Letters. - : Seismological Society of America (SSA). - 0895-0695 .- 1938-2057. ; 80:1, s. 159-160
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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- Dineva, Savka, et al.
(författare)
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Energy magnitude : A case study for southern Ontario/western Quebec (Canada)
- 2009
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Ingår i: Seismological Research Letters. - : Seismological Society of America (SSA). - 0895-0695 .- 1938-2057. ; 80:1, s. 136-148
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Tidskriftsartikel (refereegranskat)abstract
- The conventional methods for rapid determination of earthquake magnitude are based mainly on peak-to-peak amplitudes of specific phases on a seismic trace. Today, broadband digital records are readily accessible in real time, enabling the use of more information from a seismogram for rapid magnitude calculation. The aim of this work is to introduce a new magnitude scale for routine seismological analysis, denoted ME (P-wave, S-wave+coda, or both). This magnitude scale uses the signal energy and is illustrated here with a case study from southern Ontario/western Quebec (Canada). Traditional types of magnitude scales, based on the estimated maximum velocity (mb) and Richter local magnitude (ML), as well as the moment magnitude (MW), and some other magnitude types, based on the coda energy (MCoda) and ehvelope area (MEnv) are also computed for the study area for comparative purposes. Ihe proposed approach employed for this study can be easily applied to any other region of the world. The developed automatic procedure allowed the simultaneous computation of different magnitudes and different trace components and types of waves. The data used for this research are from 238 well-recorded earthquakes between 1991 and 2006 in southern Ontario/western Quebec/northern Ohio/northern NY State (1.0 < mN < 5.5). The results of our work show that, in general, magnitude values based on signal energy ME give less scattered estimates than magnitude values based on peak-to-peak measurements. We recommend using ME (S + coda) scale (vertical component) for quantifying the earthquakes in the study area in the future. The magnitude formula for this scale is given by ME = 0.5log ẼS + 0.92logD + 3.56 + S, where ẼS is the signal energy defined here (∑vs2 Δt, vS is measured in mm/s, Δt is the sample interval in seconds), D is the epicentral distance in km, and S is the station correction. The new ME magnitude can be used for a quick estimate of the MW magnitude for the study region using the relationship: MW = ME - 0.51 (for earthquakes with ME ≥ 2.6), obtained here.
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- Dineva, Savka, et al.
(författare)
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Fluid-moderated seismicity in Great Lakes?
- 2002
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Ingår i: Seismological Research Letters. - 0895-0695 .- 1938-2057. ; 73:2, s. 254-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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- Dineva, Savka, et al.
(författare)
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Georgian Bay (Ontario) earthquake with magnitude m (sub N) 4.3 (October 20, 2005) and its foreshock-aftershock sequence; : tectonic implications
- 2006
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Ingår i: Seismological Research Letters. - 0895-0695 .- 1938-2057. ; 77:2, s. 294-
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Tidskriftsartikel (refereegranskat)abstract
- On October 20 2005 at 21:16 GMT, a magnitude mN 4.3 earthquake occurred in the southern part of Georgian Bay, approximately 12 km north of Thornbury, Ontario, Canada (latitude 44.67° N and longitude 80.46° W). This earthquake is the largest one in southern Ontario recorded by a local seismograph network and is of particular interest due to its location 90 km from a proposed long-term storage facility for high-level nuclear waste. The earthquake was felt along the southern shore of Georgian Bay with maximum intensity of IV MM. During the first 24 hours after the earthquake occurred, four portable ORION seismograph systems were installed to record possible aftershocks. The main shock on October 20 2005 was preceded by a foreshock 30 sec before it, and was followed by 5 aftershocks within 4-day period. All the epicenters of the foreshock and aftershocks were within 2.5 km from the epicenter of the main shock. The large amount of available data from the recently installed broad-band POLARIS seismograph stations, as well as the permanent CNSN stations and the temporary stations, gave us a unique opportunity to study the parameters of this event. The analysis of the foreshock-main shock-aftershock sequence indicated focal depths around 7 to 12 km. The focal mechanism calculated from the polarities of P-arrivals showed predominantly thrust mechanism of the main shock, with nodal planes oriented almost NW-SE. The focal mechanism is very similar to the predominant focal mechanism of the earthquakes in Western Quebec Seismic Zone but different from the predominant strike-slip focal mechanisms south of Lake Erie and the oblique slip mechanisms in western Lake Ontario. Aeromagnetic data reveal a prominent NW-SE structural fabric for the basement rocks beneath Georgian Bay, in good agreement with the orientation of the nodal planes. This structural fabric probably reflects mafic dykes (the Matachewan dyke swarm). The spectra of S-waves, recorded at 13 bedrock stations, were fitted with Brune’s model and used to calculate the seismic moment (3.6e+14 N.m), source radius (~ 400 m), stress drop (~ 20 bars), and moment magnitude (Mw 3.7). This seismic moment and calculated focal mechanism were used as initial approximation for seismic moment tensor inversion. The results of the inversion showed correspondence between the seismic moment and double-couple focal mechanism calculated from the moment tensor
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- Dineva, Savka, et al.
(författare)
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High Precision Magnitude Measurements Using Total Signal Energy of P- and S-Wave Trains
- 2007
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Ingår i: Seismological Research Letters. - 0895-0695 .- 1938-2057. ; 78:2, s. 249-250
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Tidskriftsartikel (refereegranskat)abstract
- The conventional methods for determining the magnitude of an earthquake such as Richter magnitude, Nuttli magnitude etc. are based mainly on peak-to-peak amplitudes of different phases on the seismic trace. These magnitude scales were developed in the past during the days when we had only paper seismic recordings. The conventional method for determining moment magnitude obtained from seismic moment is measured actually as the low frequency level of the displacement spectrum. Both of the above mentioned methods ignore a lot of the information, which is provided in a modern digital 3-component seismogram. In this study we explore the applicability of total signal energy as the main parameter to be used in magnitude estimation. Over 2100 three-component seismic traces from 258 local and regional earthquakes recorded on the Southern Ontario Seismic /POLARIS networks were used in this study. To relate the new energy magnitude scale to the old ones, including Mw, we have calculated most known magnitude types and the seismic moment of the earthquakes. To carry out this work, an automatic procedure was developed for measuring the peak-to peak amplitudes, periods, duration, and signal energy for each seismic trace. For calculation of the seismic moment, an iterative technique was developed to separate the effects of source functions from site response and geometrical spreading and attenuation effects. We have compared our energy magnitude measurements with the other well-known magnitude measurements by monitoring the solution errors. Our results show that the measurements of total seismic signal energy in both the P- and S-wave trains can improve the precision of the earthquake magnitude significantly and reduce much of the scatter found in conventional magnitude measurements.
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