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  • 1.
    Adamaki, Angeliki K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Precursory Activity Before Larger Events in Greece Revealed by Aggregated Seismicity Data2017In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 174, no 3, p. 1331-1343Article in journal (Refereed)
    Abstract [en]

    We investigate the seismicity rate behaviour in and around Greece during 2009, seeking significant changes in rate preceding larger events. For individual larger events it is difficult to clearly distinguish precursory rate changes from other, possibly unrelated, variations in seismicity. However, when we aggregate seismicity data occurring within a radius of 10 km and in a 50-day window prior to earthquakes with, e. g. magnitude C3.5, the resulting aggregated time series show a clearly increasing trend starting 2-3 weeks prior to the "mainshock'' time. We apply statistical tests to investigate if the observed behaviour may be simply consistent with random (poissonian) variations, or, as some earlier studies suggest, with clustering in the sense that high activity rates at some time may imply increased rates later, and thus (randomly) greater probability of larger coming events than for periods of lower seismicity. In this case, rate increases have little useful predictive power. Using data from the entire catalogue, the aggregated rate changes before larger events are clearly and strongly statistically significant and cannot be explained by such clustering. To test this we choose events at random from the catalogue as potential "mainshocks''. The events preceding the randomly chosen earthquakes show less pronounced rate increases compared to the observed rate changes prior to larger events. Similar behaviour is observed in data sub-sets. However, statistical confidence decreases for geographical subsets containing few "mainshocks'' as it does when data are weighted such that "mainshocks'' with many preceding events are strongly downweighted relative to those with fewer. The analyses suggest that genuine changes in aggregated rate do occur prior to larger events and that this behaviour is not due to a small number of mainshocks with many preceding events dominating the analysis. It does not automatically follow that it will be possible to routinely observe precursory changes prior to individual larger events, but there is a possibility that this may be feasible, e. g. with better data from more sensitive networks.

  • 2.
    Beiki, Majid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Comment on ‘’Depth estimation of simple causative sources from gravity gradient tensor invariants and vertical component’’: by B. Oruç in Pure Appl. Geophys. 167 (2010), 1259–12722012In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 169, no 1-2, p. 275-277Article in journal (Refereed)
    Abstract [en]

    ORUÇ (2010) proposes a new method for interpretation of gravity gradient tensor (GGT) data. This method seems interesting in theoretical point of view, although, we have found some flaws in the equations he has derived. In this paper, we correct the introduced equations and describe some theoretical points, briefly.

  • 3.
    Oskooi, B.
    et al.
    Institute of Geophysics, University of Tehran, Tehran, Iran.
    Mansoori, I
    Institute of Geophysics, University of Tehran, Tehran, Iran.
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    A Magnetotelluric Survey on Ophiolites in Neyriz area of southwestern Iran2015In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 172, p. 491-502Article in journal (Refereed)
    Abstract [en]

    A wide band magnetotelluric study of the ophiolitic zone of the Zagros orogenic belt was conducted in the Neyriz area of southwestern Iran. The purpose of the study was to image subsurface structures electrically and relocate the main Zagros thrust fault in the region. The thrust fault has a complex structure with obscure behavior and is believed to be located within a zone of ongoing continental plate convergence. The fault zone with a NW–SE geological trend is parallel to the Zagros orogenic belt and separates the Neyriz ophiolite assemblage from the adjacent Sanandaj-Sirjan metamorphic zone. Magnetotelluric data were collected along a SW–NE profile across the geologic strike; the study included 18 stations and modeling was performed using a 2-D inversion scheme. Analysis of both modes of magnetotelluric data (TE and TM) clarifies the signatures of large resistivity variation in the study area. Due to the presence of a high contrast in resistivity between the ophiolites and neighboring rocks, we are able to discern two sharp boundaries as faulting planes and borders of the ophiolite–radiolarite zone in the north-eastern and southwestern parts of the 2-D resistivity models, respectively.

  • 4. Oskooi, B.
    et al.
    Mansoori, I.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    A Magnetotelluric Survey of Ophiolites in the Neyriz area of southwestern Iran2015In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 172, no 2, p. 491-502Article in journal (Refereed)
    Abstract [en]

    A wide band magnetotelluric study of the ophiolitic zone of the Zagros orogenic belt was conducted in the Neyriz area of southwestern Iran. The purpose of the study was to image subsurface structures electrically and relocate the main Zagros thrust fault in the region. The thrust fault has a complex structure with obscure behavior and is believed to be located within a zone of ongoing continental plate convergence. The fault zone with a NW-SE geological trend is parallel to the Zagros orogenic belt and separates the Neyriz ophiolite assemblage from the adjacent Sanandaj-Sirjan metamorphic zone. Magnetotelluric data were collected along a SW-NE profile across the geologic strike; the study included 18 stations and modeling was performed using a 2-D inversion scheme. Analysis of both modes of magnetotelluric data (TE and TM) clarifies the signatures of large resistivity variation in the study area. Due to the presence of a high contrast in resistivity between the ophiolites and neighboring rocks, we are able to discern two sharp boundaries as faulting planes and borders of the ophiolite-radiolarite zone in the north-eastern and southwestern parts of the 2-D resistivity models, respectively.

  • 5.
    Place, Joachim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Blake, O.
    Faulkner, D.
    Rietbrock, A.
    Wet Fault or Dry Fault? A Laboratory Approach to Remotely Monitor the Hydro-Mechanical State of a Discontinuity Using Controlled-Source Seismics2014In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 171, no 11, p. 2887-2897Article in journal (Refereed)
    Abstract [en]

    Stress variation and fluid migration occur in deformation zones, which are expected to affect seismic waves reflected off or propagating across such structures. We developed a basic experimental approach to monitor the mechanical coupling with respect to seismic coupling across a single discontinuity between a granite sample in contact with a steel platen. Piezoceramics located on the platen were used to both generate and record the P and S wave fields reflected off the discontinuity at normal incidence. This way, normal (B (n) ) and tangential (B (t) ) compliances were calculated using Schoenberg's linear slip theory (Schoenberg, J Acoust Soc Am 68:1516-1521, 1980) when the roughness, the effective pressure (P (eff), up to 200 MPa), and the nature of the filling (gas or water) vary. We observe that increasing the effective pressure decreases B (n) and B (t) , which is interpreted as the effect of the closure of the voids at the interface, permitting more seismic energy to be transmitted across the interface. Values of B (n) are significantly higher than those of B (t) at low P (eff) (< 60-80 MPa) in dry conditions, and significantly drop under water-saturated conditions. The water filling the voids therefore helps to transmit the seismic energy of compressional waves across the interface. These results show that the assumption B (n) a parts per thousand B (t) commonly found in some theoretical approaches does not always stand. The ratio B (n) /B (t) actually reflects the type of saturating fluids and the effective pressure, in agreement with other experimental studies. However, we illustrate that only the relative variations of this ratio seem to be relevant, not its absolute value as suggested in previous studies. Consequently, the use of B (n) against B (t) plots may allow effective pressure variation and the nature of the pore fluid to be inferred. In this respect, this experimental approach at sample scale helps to pave the way for remotely monitoring in the field the hydro-mechanical state of deformation zones, such as seismogenic faults, fractured reservoirs, or lava conduits.

  • 6.
    Raeesi, Mohammad
    et al.
    Bergen, Norway..
    Zarifi, Zoya
    Department of Earth Sciences, University of Western Ontario, London, Canada..
    Nilfouroushan, Faramarz
    Univ Gavle, Dept Ind Dev IT & Land Management, Gavle, Sweden.; Lantmateriet, Gavle, Sweden..
    Boroujeni, Samar Amini
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tiampo, Kristy
    Univ Colorado, CIRES, Boulder, CO USA.; Univ Colorado, Dept Geol Sci, Boulder, CO USA..
    Quantitative Analysis of Seismicity in Iran2017In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 174, no 3, p. 793-833Article in journal (Refereed)
    Abstract [en]

    We use historical and recent major earthquakes and GPS geodetic data to compute seismic strain rate, geodetic slip deficit, static stress drop, the parameters of the magnitude-frequency distribution and geodetic strain rate in the Iranian Plateau to identify seismically mature fault segments and regions. Our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle, with the possibility of generating major earthquakes. These faults primarily are located in the north and the east of Iran. Four seismically mature regions in southern Iran with the potential for damaging strong earthquakes are also identified. We also delineate four additional fault segments in Iran that can generate major earthquakes without robust clues to their maturity. The most important fault segment in this study is the strike-slip system near the capital city of Tehran, with the potential to cause more than one million fatalities.

  • 7.
    Rashidi, Amin
    et al.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran, Iran.
    Farajkhah, Nasser Keshavarz
    RIPI, Tehran, Iran.
    Tsunami Simulations in the Western Makran Using Hypothetical Heterogeneous Source Models from World's Great Earthquakes2018In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 175, no 4, p. 1325-1340Article in journal (Refereed)
    Abstract [en]

    The western segment of Makran subduction zone is characterized with almost no major seismicity and no large earthquake for several centuries. A possible episode for this behavior is that this segment is currently locked accumulating energy to generate possible great future earthquakes. Taking into account this assumption, a hypothetical rupture area is considered in the western Makran to set different tsunamigenic scenarios. Slip distribution models of four recent tsunamigenic earthquakes, i.e. 2015 Chile M-w 8.3, 2011 Tohoku-Oki M-w 9.0 (using two different scenarios) and 2006 Kuril Islands M-w 8.3, are scaled into the rupture area in the western Makran zone. The numerical modeling is performed to evaluate near-field and far-field tsunami hazards. Heterogeneity in slip distribution results in higher tsunami amplitudes. However, its effect reduces from local tsunamis to regional and distant tsunamis. Among all considered scenarios for the western Makran, only a similar tsunamigenic earthquake to the 2011 Tohoku-Oki event can re-produce a significant far-field tsunami and is considered as the worst case scenario. The potential of a tsunamigenic source is dominated by the degree of slip heterogeneity and the location of greatest slip on the rupture area. For the scenarios with similar slip patterns, the mean slip controls their relative power. Our conclusions also indicate that along the entire Makran coasts, the southeastern coast of Iran is the most vulnerable area subjected to tsunami hazard.

  • 8.
    Siksna, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    A symmetrical aspiration capacitor for the simultaneous recording of atmospheric ions of both polarities1972In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 100, no 8, p. 146-153Article in journal (Refereed)
    Abstract [en]

    With the ordinary aspiration-capacitor, ions of only one polarity can be detected, and for the simultaneous measurement of ions of both polarities, two such counters are necessary. For the investigation of the transient phenomena in an aspiration-capacitor, a symmetrical plate capacitor has been constructed. When each of the plates is connected to a separate electrometer, ions of one polarity can be recorded by one of the electrometers connected to one of the plates and ions of the other polarity by the electrometer connected to the other plate. The advantage of the symmetrical aspiration-capacitor described is that ions of both polarities contained in the same air volume can be simultaneously recorded.

  • 9.
    Zarifi, Zoya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Nilfouroushan, Faramarz
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Raeesi, Mohammad
    Department of Earth Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway.
    Crustal stress Map of Iran: Insight from seismic and geodetic computations2014In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 171, no 17, p. 1219-1236Article in journal (Refereed)
    Abstract [en]

    We used the focal mechanisms of crustal earthquakes (depth <40 km) in the period 1909-2012 and the available GPS velocities, estimated from the data collected between 1999 to 2011, to estimate the magnitude and directions of maximum principal stress and strain rates in Iran. The Pearson product moment correlation was used to find the correlation between the stress field obtained from the focal mechanism stress inversion and that obtained using the seismic and geodetic strain rates. Our assumption is that stresses in a continuum are produced by tectonic forces and the consequent deformation on the crustal scale. Therefore, the direction of the stress and strain (or strain rate) are ideally be the same. Our results show a strong correlation between the directions of the principal components of stress and strain (rate) obtained using the different data/methods.  Using  weighted average analysis, we present a new stress map for Iran.

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