Type of research: basic Duration from: 06/01/91. to 12/31/93. Papers on project (total): 0
Institution name: Građevinski fakultet, Split (83) Department/Institute: HYDRAULIC DEPARTMENT OF STRUCTURES Address: MATICE HRVATSKE 15 City: 21000 - Split, Croatia
Communication
Phone: 385 (0)21 52 33 33
Fax: 385 (0)21 52 41 62
E-mail: stojic@cigla.gradst.hr
Summary: INFLUENCE OF MAN MADE LAKES ON EARTHQUAKS
The phenomenon of earthquake by water storage reservoirs was discovered
before the Second World War on the Marathon dam in Greece - l930, on the
Qued Fodda dam in Algiers - 1933 and on the Hoover dam (Boulder) in USA -
1935. The public all over the world was the first time warned of that
danger by the French Committee for High Dams in 1967. The same year the
Committee for High Dams of former Yugoslavia declered that three
seismographs were installed on the Grančarevo dam (1965) in order to
study the eartquakes caused by water storage reservoir in karst areas.
A number of research works carried out in various countries have
indicated that man made lake might be cause of seismic activity. Seismic
movements of the earth's crust on large areas, or the macro- seismic
earthquakes, are an important factor to be taken into consideration in
selecting a dam site in design of dams. However, in large region of equal
degree of macro-seismic activity, areas may have differences in local
seismic characteristics. Such a local micro-seismic activity has often
neglected in investigations, design and constuction. Large dams and man
made lakes are considered as "passive factors" in terrain movements
caused bu natural forces. Recent informations indicate that large dams
and storage reservoirs may cause earthquakes of both the macro-seismic
and micro-seismic nature. In such seismic movements the dam and the
reservoir are "active factors" which influence the seismic processes in
the earth's crust. Consequently, two types of earthquakes have to be
distinguished, as the two variants of seismic activity, namely the
seismic activity influenced by naturel forces, and seismic activity
influenced by storage reservoirs. Significant experiences were
accumulated in many countries. Systematic observations and investigation
of eventual effects of storage reservoir on induced sesmicity was
initiated with construction of the system of hydroelectric power plants
on the Trebišnjica River, one of the largest subterranean karst river in
Europe. It sinks undergound in Popovo Polje after a course of about 100
km, with outflowing either close to the Adriatic Sea or at the Neretva
River. By creating the reservoir (V = 1,3 *10**9 m3) the Trebišnjica
River Springs were flooded by 77 m. The construction of Grančarevo
Arch Dam ( 123 m high) started in 1960., foundation excavations
initiated in 1964. Special highly sensitive seismographs have be put in
operation on Febuary 6, 1965. Filling of the reservoir began on
November 1, 1967. Filling of the reservoir causes changes in seismic
activity evenat great distances from the reservoir (75 km). The seismic
activity measured by the number and total released energy of eartquakes
increased after start of filling of the reservoir. A noticeable increase
in seismic activity has occured for the reservoir depths of over 6o m.
During the initial cycles of loading and unloading of the reservoir, the
seismic activity is evidently affected by reservoir levels. The
correlation coefficient (linear regression) between the monthly number of
earthquakes of each hudrological year (1st November past year - 31st
October next year) and correspoding mean monthly water height in the
reservoir indicate strong association during first four cycles of
reservoir loading and unloading (r = 0,82 - 0,90). According to the
records detected with instruments, for the period after filling the
reservoir 11.1.1967. - 10.31.1990., were 16.751 earthquakes with released
energy E =5,3*10**10 J. The strongest earthquake within the region
around the reservoir happened October 3, 1979. with magnitude M=4,9.
With increase of the earthquake epicenter distance from the dam the
energy released also increase. The released energy is inversely
proportional to the number of eartquakes; the higher the number of
earthquakes the less energy they release.
Keywords: dams, man made lakes, storage reservoirs, filling, induced seismicity, earthquakes, released energy, correllation, mathematical statistics, probability, karst areas, Grančarevo dam.
Research goals: According the collected data for 23 hidrological
year are calculated correlation coefficients from number of earthquakes
and corresponding monthly water lavels. Filling of the reservoir causes
changes in induced seismicity.
COOPERATION - INSTITUTIONS
Name of institution
: HRVATSKA ELEKTROPRIVREDA - suradnik:
Istraživać LALIĆ RODOLJUB Type of institution: Economical/Production Type of cooperation: Joint project City: 21000 - Split, Croatia Other information about the project.