HORIZONTAL DEFORMATION BEFORE AND AFTER THE TANGSHAN EARTHQUAKE OF 1976

With the so-called model of 'Homogeneous Separate Blocks', data from seven thimes of triangulation or trilateration since 1954 have been analysed in this paper to study the rock deformation before and after the Tangshan earthquake of 1976.Some new finding is obtained as follows:1) Between 1964 and 1971 the Tangshan rhomb block moved towards NNE.2) Compressive strain accumulated within the rhomb block.3) At least in the shallow part of the crust the seismogenic fault of the Tangshan earthquake was locked before the quake.So far, these characteristics might be the relatively reliable information about horizontal rock deformation in a large area before the quake.Limited by the accuracy of existing observations, no remarkable deformation was detected after the quake According to the not so reliable results obtained from two measurements carried out within one year after th quake it might be inferred that in the adjusting period lasting for one year after the quake the relative motion between the two sides of the seismic fault might be contrary to that during the seismic event but much smaller in extent. At present no significant deformation can be detected in the Tangshan area.