Zdenka Schenková

The probability of occurrence of largest earthquqkes in the European area — Part II

SummaryThe previous investigation of the probability of occurrence of largest earthquakes in the European area continued by applying the Gumbel theory of largest values to three periods 1901–1930, 1901–1955 and 1901–1967, respectively. The values of magnitudes which will be exceeded with the probabilityP=1%, 2% and 10% were determined from the lines fitting the distributions of magnitudes and corresponding probabilities for all three periods. It was assumed that the relationship between the differences δMP%[k](67)=Mk,P%−M67,P% (k=30, 55, 67) and the observation period follow the hyperbolic law. This tendency was used for the estimation of the probability line corresponding to an infinite observation period.

Model of earthquake occurrence in the European area

SummaryThe time distribution of earthquake occurrence in the European area is investigated by statistical laws. The original data of shallow-focus earthquakes are taken from the European catalogue 1901–1967. Evidence is given that the process with the negative binomial entries as a model describing the occurrence of shallow-focus earthquakes is better than the Poisson process. Further, the influence of magnitude classes and magnitude threshold value on the time distribution of earthquake occurrence is examined.

Seismicity of the north-eastern region (N.E.R.) of India

SummaryThe earthquake pattern in the N.E.R. of India is investigated on the background of tectonic conditions. The epicentre maps and the cross-sections indicate some regularities in the spatial distribution of foci, particularly the existence of a Benioff zone, dipping down to 200 km at an angle of 35°–40° to the East between 25° N and 21° N. The shallow and intermediate activities in the Indoburmese zone seem to be mutually related as evidenced by the coincidence of periods of quiescence and activity. The origin of the largest of the whole region (15 Aug. 1950, M=8.6) can be accommodated in the statistics only by assuming a very large preparatory area also encompassing the “extended” Mishmi region. This event seems to be a rather exceptional event with the return period larger than the sample used for investigation, i.e. 54 years. The problem of a gap in the region of the Upper Assam remains open, the lack of activity also be explained also by pure geological reasons, i.e. by the age of the stable geological formation. The maps and the statistics of extremes provide the estimate of probability of occurrence of large events for practical purpose.

Reply to comment by J. Mrlina et al. on “Crustal deformations in the epicentral area of the west Bohemia 2008 earthquake swarm in central Europe”

GPS campaigns were performed in West Bohemia by the Institute of Rock Structure and Mechanics (IRSM) and the Institute of Geophysics (IG), both a part of the Academy of Sciences of the Czech Republic. To compare results from both campaigns, data must be processed using identical conditions. Unfortunately, the satellite signal monitoring and data processing applied by both Institutes differed substantially. The IG campaigns were stated as follows by Mrlina and Seidl [2008]: “performed with five GPS receivers in a five-days-long main campaigns under a constant plan of receivers/antennas rotation on particular sites. The methodology was aimed at suppression of the antenna center effects by observations with at least 2 different GPS sets at each point during one campaign and in different satellite geometry; it means not 1 GPS set at 1 point only”. The signals were processed using Trimble Total Control software v.2.73 which calculates the site positions fixed to one permanent NKIG station in Nový Kostel [Mrlina et al., 2014, henceforth, Comm]. The IRSM annual campaigns continuously monitored signals for two GPS days together at all sites and always with identical antennas at every site [Schenk et al., 2012, henceforth, S2012]. Signals were processed using Bernese software v.5 [Hugentobler et al., 2005], which calculates site positions in the defined ITRF: the EPN (BOR1, PENC, and ZIMM) and GEONAS stations (KYNS, LUBY, MARJ, and POUS) [Schenk et al., 2010b] as fiducial stations. All of the corrections required to reach highly precise positions were applied [S2012; Schenk et al., 2010a].