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  • 1. Dineva, Savka
    et al.
    Eaton, Daniel D.W.
    Department of Earth Sciences, University of Western Ontario.
    Mereu, Robert F.
    Department of Earth Sciences, University of Western Ontario.
    Eaton, David W.S.
    Department of Earth Sciences, University of Western Ontario.
    Seismicity of the southern Great Lakes: Revised earthquake hypocenters and possible tectonic controls2004Ingår i: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 94, nr 5, s. 1902-1918Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using data from 27 seismograph stations for the period 1990-2001, we have relocated 106 hypocenters of earthquakes with magnitudes from 0.9 to 5.4 in the region of the southern Great Lakes. Two complementary methods were used for relocation: a conventional least-squares approach (Lienert and Havskov, 1995) and joint hypocentral determination (Pujol, 2000). These two methods yielded mutually consistent spatial patterns of seismicity with an average difference of 3.7 km in epicentral locations and 1.1 km in focal depths. We show that the hypocenter locations are not very sensitive to realistic uncertainties in 1D crustal velocity. Our sharpened definition of zones of seismicity delineates several clusters beneath Lake Ontario, around Niagara Falls, and near the south shore of Lake Erie. These seismicity zones appear to correlate with areas where the regional magnetic data exhibit prominent short-wavelength (<5 km) linear anomalies. The magnetic anomalies are associated with basement structures that formed during the Precambrian (Mesoproterozoic) Grenville orogen. Both the seismicity and magnetic anomalies exhibit statistically significant preferred orientations at N40°E-N45°E, but the correlation of the earthquake clusters with specific aeromagnetic lineaments remains uncertain. Three preliminary focal mechanisms of earthquakes with magnitudes mN 3.1 to 3.8 show unusual normal faulting, with nodal planes in almost the same direction as the magnetic trends, N42°E-N52°E. Proximity of the earthquake clusters to large bodies of water, coupled with colinearity with magnetic anomaly trends, suggests that both surface water and pre-existing basement structures may play significant roles in controlling intraplate seismicity in the southern Great Lakes region

  • 2. Dineva, Savka
    et al.
    Eaton, David W.S.
    Department of Geoscience, University of Calgary.
    Reply to "Comment on 'The October 2005 Georgian Bay, Canada, earthquake sequence: Mafic dykes and their role in the mechanical heterogeneity of precambrian crust' by S. Dineva, D. Eaton, S. Ma, and R. Mereu" By G. Ranalli and M. Lamontagn2010Ingår i: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 100, nr 1, s. 406-407Artikel i tidskrift (Övrigt vetenskapligt)
  • 3. Dineva, Savka
    et al.
    Eaton, David W.S.
    Department of Earth Sciences, University of Western Ontario.
    Ma, Shutian
    Department of Earth Sciences, University of Western Ontario.
    Mereu, Robert F.
    Department of Earth Sciences, University of Western Ontario.
    The October 2005 Georgian Bay, Canada, earthquake sequence: Mafic dykes and their role in the mechanical heterogeneity of Precambrian crust2007Ingår i: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 97, nr 2, s. 457-473Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On 20 October 2005 at 21:16 UTC, a moderate earthquake (mN 4.3) occurred in an area of low seismicity within Georgian Bay, approximately 12 km north of Thornbury, Ontario (44.67° N, 80.46° W). Despite its moderate magnitude, it was exceptionally well recorded and is of particular interest because of its location 90 km from a proposed long-term storage facility for low- and medium-level nuclear waste. No damage was reported, but ground shaking was felt to a distance of 100 km. Within 24 hours after the mainshock, four portable seismograph systems were installed in the epicentral region. In total, eight events were recorded over a 4-day period, including a foreshock and six aftershocks. The unusually rich dataset from this moderate earthquake sequence enabled robust determination of hypocentral parameters, including well-constrained focal depths for most events. For the mainshock, we estimated a seismic moment of M0 4.5 × 1014 N m and corner frequency of 3.7 Hz, based on a spectral fit using Brune's source model. Least-squares waveform inversion of P and S phases yielded a double-couple focal mechanism with a reverse-sense of slip and northwest-striking nodal planes. The reverse mechanism and mid-crustal focal depths (10-12 km) are characteristic, in general, of more abundant seismicity located ∼200 km northeast of this event in the western Quebec seismic zone. These parameters differ, however, from shallow (2-6 km) earthquakes, with predominantly strike-slip mechanisms, observed near Lake Erie ∼200 km to the south. We attribute this north-south change in rupture mechanism to variations in crustal stress induced by postglacial isostatic rebound. Aeromagnetic data in and around the epicentral region reveal prominent northwest-striking lineations caused by Precambrian mafic dykes. Under midcrustal conditions, the dyke material is mechanically stronger than generally more felsic upper-crustal host rocks. We propose that where large dykes are favorably oriented with respect to the stress field, they may strongly influence the locations of intraplate earthquake rupture in Shield regions.

  • 4.
    Mihaylov, Dimitar
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    El Naggar, Mohamed Hesham
    Department of Civil and Environmental Engineering, Faculty of Engineering, University of Western Ontario.
    Dineva, Savka
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Separation of high- and low-level ambient noise for HVSR: Application in city conditions for Greater Toronto area2016Ingår i: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 106, nr 5, s. 2177-2184Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Nakamura method, which involves horizontal-to-vertical spectral ratio (HVSR) analysis, is widely used for seismic microzonation studies. The noise from local traffic in city conditions presents a challenge for the application ofHVSR analysis. This article presents a technique developed for separation of the transient noise due to local traffic (high-level noise) and background ambient noise (low-level noise) and the application of theHVSR analysis to both partitions of the noise. This approach is applied to identify the predominant frequencies for almost 200 noise samples from the Greater Toronto area. The results demonstrated that the developed technique is effective and allows estimation of the fundamental resonant frequency in theHVSR in urban environment, even in the presence of intensive nearby traffic. The interpretation of the obtained results showed that, most probably, the lower (fundamental) frequency appears due to multiple reflections from the overburden/bedrock boundary. In some cases, a resonance with higher amplitude is dominant, and it is due to a contrast boundary between soil layers in the overburden

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