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3D Real Time Network in Ohrid

The 3D strong motion recording network in Ohrid was founded in 1976. The aim was to install a local 3D network of three component accelerographs for recording weak and strong earthquake motions, ambient and forced vibrations in order to provide information for experimental and theoretical investigations of  fundamental problems in engineering seismology and earthquake engineering related to the influence of the seismic motion propagation characteristics, local soil, foundation-soil interaction and seismic response of structures.

The Debar-Ohrid region was chosen because of its pronounced seismic activity that can generate earthquakes with magnitudes M>6 according to the Richter scale. The network was installed in the period 1981-1985. Regarding the goals and the expected results, the eastern part of the city of Ohrid (Fig.2) was chosen as the most suitable location. The network consists of five individual sets of instruments (Fig. 3) that are connected to a standard time code receiver. Individual systems are located on bedrock (1), characteristic soil (3) and buildings (1) (Table 3).

In 2009, the instrument array was modernized, i.e., the network was upgraded by replacement of the old recording system by a real time monitoring system.

Fig.2 Plan of sites of the Ohrid lake strong motion three dimensional array
L1 – Building site; L2 and L3 ¬characteristic soil; L4 – Outcropping rock


Table 3 Characteristics of the Ohrid 3D Strong Motion Array
Location-1 Location-2 Location-3 Location-4
Site Type Instrumented Building Free-field Free-field Rock-outcrop
Instrument Position
Building 2(6-th and 9-th story)
Foundation 4
Surface 1 1 1 1
In-profile 2(-13.0 and -22.9m) 2(-9.5 and -22.0m) 2(-9.0 and -21.5m)
Bedrock 1(-101.0m) 1(-125.0m) 1(-99.6m)
Total Number of Instruments 10 4 4 1


Fig.3 Distribution of instruments at Location 1(instrumented building site)