@article{KulikovaKrueger2015, author = {Kulikova, Galina and Kr{\"u}ger, Frank}, title = {Source process of the 1911 M8.0 Chon-Kemin earthquake: investigation results by analogue seismic records}, series = {Geophysical journal international}, volume = {201}, journal = {Geophysical journal international}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggv091}, pages = {1891 -- 1911}, year = {2015}, abstract = {Several destructive earthquakes have occurred in Tien-Shan region at the beginning of 20th century. However, the detailed seismological characteristics, especially source parameters of those earthquakes are still poorly investigated. The Chon-Kemin earthquake is the strongest instrumentally recorded earthquake in the Tien-Shan region. This earthquake has produced an approximately 200 km long system of surface ruptures along Kemin-Chilik fault zone and killed about similar to 400 people. Several studies presented the different information on the earthquake epicentre location and magnitude, and two different focal mechanisms were also published. The reason for the limited knowledge of the source parameters for the Chon-Kemin earthquake is the complexity of old analogue records processing, digitization and analysis. In this study the data from 23 seismic stations worldwide were collected and digitized. The earthquake epicentre was relocated to 42.996NA degrees and 77.367EA degrees, the hypocentre depth is estimated between 10 and 20 km. The magnitude was recalculated to m(B) 8.05, M-s 7.94 and M-w 8.02. The focal mechanism, determined from amplitude ratios comparison of the observed and synthetic seismograms, was: str = 264A degrees, dip = 52A degrees, rake = 98A degrees. The apparent source time duration was between similar to 45 and similar to 70 s, the maximum slip occurred 25 s after the beginning of the rupture. Two subevents were clearly detected from the waveforms with the scalar moment ratio between them of about 1/3, the third subevent was also detected with less certainty. Taking into account surface rupture information, the fault geometry model with three patches was proposed. Based on scaling relations we conclude that the total rupture length was between similar to 260 and 300 km and a maximum rupture width could reach similar to 70 km.}, language = {en} } @article{PassarelliHainzlCescaetal.2015, author = {Passarelli, Luigi and Hainzl, Sebastian and Cesca, Simone and Maccaferri, Francesco and Mucciarelli, Marco and R{\"o}ßler, Dirk and Corbi, Fabio and Dahm, Torsten and Rivalta, Eleonora}, title = {Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy}, series = {Geophysical journal international}, volume = {201}, journal = {Geophysical journal international}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggv111}, pages = {1553 -- 1567}, year = {2015}, abstract = {Tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency-magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg-Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M-w = 4.2 and M-w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M-l > 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been 'passive' features, with small fault patches failing on largely locked faults, or may have been accompanied by an 'active', largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area.}, language = {en} } @article{GhodsShabanianBergmanetal.2015, author = {Ghods, Abdolreza and Shabanian, Esmaeil and Bergman, Eric and Faridi, Mohammad and Donner, Stefanie and Mortezanejad, Gholamreza and Aziz-Zanjani, Asiyeh}, title = {The Varzaghan-Ahar, Iran, Earthquake Doublet (M-w 6.4, 6.2): implications for the geodynamics of northwest Iran}, series = {Geophysical journal international}, volume = {203}, journal = {Geophysical journal international}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggv306}, pages = {522 -- 540}, year = {2015}, abstract = {On 2012 August 11, a pair of large, damaging earthquakes struck the Varzaghan-Ahar region in northwest Iran, in a region where there was no major mapped fault or any well-documented historical seismicity. To investigate the active tectonics of the source region we applied a combination of seismological methods (local aftershock network, calibrated multiple event relocation and focal mechanism studies), field observations (structural geology and geomorphological) and inversions for the regional stress field. The epicentral region is north of the North Tabriz Fault. The first main shock is characterized by right-lateral strike-slip motion on an almost E-W fault plane of about 23 km length extending from the surface to a depth of about 14 km. The second main shock occurred on an ENE-striking fault that dips at 60-70A degrees to the NW. Independent inversions of focal mechanisms and geologically determined fault kinematic data for the active stress state yield a transpressional tectonic regime with sigma(1) oriented N132E. For the region northeast of the North Tabriz Fault, the presence of rigid lithosphere of the South Caspian Basin implies the kinematic adjustment by northward transferring of the contracted masses through both distributed deformation and structural deflections. Our results suggest that the kinematic adjustment inside a contracting wedge may occur along interacting crosswise or conjugate faults to accommodate low rates of internal deformation. At a global scale, our results indicate that despite the basic assumption of 'rigid blocks' in geodetic plate modelling, internal deformation of block-like regions could control the kinematics of deformation and the level of seismic hazard within and around such regions of low deformation rate.}, language = {en} }