Weak seismicity of Azerbaijan territory and its relation with modern geodynamics
Mammadli Tahir Y.
The seismic zoning of territories having greater socially, economical and ecological importance, is one of actual problems of modern seismology.
The major condition of compiling of maps of seismic zoning or their refinement is revealing source zones of large earthquakes and estimation of their seismic potential.
Weak earthquakes, unlike strong, occurs often and bear the wide information on the tectonic processes processes proceeding in a crust of Earth, including in source zones of large earthquakes. Therefore, study of features of appearance of weak seismicity about which one for last years the great amount of material is collected, and their relation with modern geodynamics has a greater urgency.
In connection with abovementioned features dimensionally – time appearance of weak seismicity of Azerbaijan have been investigated and non-uniform allocation of weak earthquakes on lateral and depth is established. Weak earthquakes in mountain and foothill zones are spread multiple and rather shallow (H£30-35km), in depression zones – a little bit smaller quantity and rather deep (H£45-50km), in Caspian sea is enough plenty and deeper (H£60-70km). Non-uniform allocation of weak shocks is observed within the limits of seismoactive zones. Their big concentration is characteristic for source zones of large earthquakes.
On the basis of laws of appearance of weak seismicity the method of eliciting source zones of large earthquakes is developed.
On the basis of method fixed submission about seismogenerating structures which are the active faults differentiating geotectonic structures with a various tectonic regime both accumulating all strong and basic mass of weak and mean force of earthquakes.
According to this method of reveal seismogenerating zones is conducted on the basis of breaking of investigated territory on uniform fields and map compiling of epicenters of weak earthquakes. For each of these platforms within the limits of which one quantity of epicenters not less set threshold number, approximating lines of concentration of epicenters are under construction. It is supposed, that these lines correspond to zones of active faults.
On the basis of this method is developed the model of active faults or source zones of strong earthquakes of Azerbaijan.
Comparison has demonstrated, that revealed source zones correspond to the active fields of deep faults of territory of republic, and the deep geodynamical processes proceeding in these fields, are imaged in seismic fields.
The spatial location seismigenerating zones revealed on weak seismicity demonstrates, that in territory of Azerbaijan any fault on all length does not exhibit identical seismic activity.
Under the analysis of proportions of length source zones (L) and magnitude (M) of earthquakes the relation between these parameters is established:
1gLkm=0, 366 M – 0,883
This relation has allowed to determine greatest possible magnitude earthquakes in seismogenerating (source) zones of Azerbaijan and to count expected seismic effect above ground.
Established that value of possible greatest earthquakes magnitude (Mmax) in territory of Azerbaijan equally Mmax = 6,9 - 7,3 and the max seismic effect
On a surface is equal J0 = 10 points on a MSK – 64.
On the basis of spatial distribution of source zones revealed on weak seismicity and values of magnitude, the greatest possible earthquakes in them, the map-scheme of a seismic hazard of territory of Azerbaijan has been compounded. On this map seismic shakes have high differentiation on spatial and intensity level.
Background level of a seismic hazard of territory is 8 points. Higher seismic hazard (10 points) is expected in a zone Shemakha – Gabala. The same level of hazard allocates small field in northern Sheki – Oguz zone.
Zones which intensity are 9 points take enough greater territories. One of them is had between latitude Hajigabul and boundary of republic Dagestan. The width of this zone encompasses territory between meridians Maraza and Sheki. Such zones are allocated also in areas Zagataly, Gases, Gandzha, Imishly – Sabirabad, to the east Jalilabad, Masally – Lenkaran and to the south Absheron.