SUNDAY, MARCH 14, 1976
ALL DATA COLLECTED ARE SENT TO THE UNITED STATES GEOLOGICAL SURVEY NATIONAL EARTHQUAKE INFORMATION SERVICE IN WASHINGTON DAILY BY TELEGRAMS AND TO THE INTERNATIONAL SEISMOLOGICAL CENTRE IN EDINBURGH EVERY THREE MONTHS FOR PROCESSING.
+RECORDS DATING BACK TO 1921 ARE ALSO BEING KEPT LOCALLY AND
WILL BE MICROFILMED FOR BETTER STORAGE, HE SAID.
THE SENSORS OF THE SEISMOGRAPHS AT THE ROYAL OBSERVATORY COMPARABLE TO THE FEELERS OF INSECTS ARE PERHAPS THE MOST HIGHLY PROTECTED INSTRUMENTS KEPT THERE.
THEY ARE PLACED WITHIN A DOUBLE-WALLED UNDERGROUND ROOM AT A CONSTANT TEMPERATURE AND HUMIDITY AND ARE PLACED ON PILLARS STRUCK DEEP IN THE GROUND.
+THERE ARE ALTOGETHER 12 SENSORS,+ MR. LAM SAID, THREE FOR EACH OF FOUR SETS OF SEISMOGRAPHS WHICH ARE SENSITIVE TO TREMORS ORIGINATING FROM DIFFERENT DISTANCES FROM HONG KONG.
+EACH OF THE THREE SENSORS IN EACH SET IS IN TURN SENSITIVE
NORTH/SOUTH,
TO TREMORS COMING FROM ONE DIRECTION AL IGNMENT
EAST/WEST, OR THE VERTICAL.+
EARTH MOVEMENTS, NORMALLY LASTING BETWEEN SEVERAL MINUTES TO SEVERAL HOURS, ARE DETECTED BY THE SENSOR AND CONVERTED TO ELECTRICAL ENERGY WHICH ACTIVATES A MIRROR GALVANOMETER,
A LIGHT BEAM REFLECTED BY THE MIRROR IS IN TURN DIRECTED ONTO
A ROLL OF ROTATING PHOTO-SENSITIVE PAPER.
THE DIRECTION, DISTANCE, AND TIME OF THE EARTHQUAKE CAN THEN BE ESTIMATED FROM THE RECORDINGS ON THE PAPER.
+THE RECORDS ARE NORMALLY TAKEN OFF FOR INSPECTION EVERY 24 HOURS,+ MR. LAM SAID.
+ INTERPRETATION OF THE READINGS REQUIRES SPECIAL TRAINING, + MR. LAM ADDED, +BECAUSE INDICATIONS OF EARTH MOVEMENTS ON THE SEISMOGRAMS COULD BE CAUSED BY THE FORCE OF SEAWAVES AGAINST THE SHORE, OR QUITE OFTEN BY PILING ON CONSTRUCTION SITES CLOSE TO THE OBSERVATORY OR BY THE RUNNING OF MOTOR VEHICLES IN ITS VICINITY.+
IF, HOWEVER, A GENUINE INTENSE EARTHQUAKE IS RECORDED THE OBSERVATORY WOULD IMMEDIATELY CONTACT EARTHQUAKE INFORMATION CENTRES IN HONOLULU AND TOKYO ASKING FOR MORE PRECISE INFORMATION ON THE LOCATION OF THE EPICENTRE OF THE EARTHQUAKE AND ITS MAGNITUDE.
HONOLULU, BEING THE CONTROL CENTRE OF THE 56-STATION PACIFIC TSUNAMI NETWORK, WILL ALSO ALERT HONG KONG TO ANY POSSIBLE TSUNAMI (AN EARTHQUAKE-GENERATED TIDAL WAVE).
THE MAGNITUDE OF A TSUNAMI, IF THERE IS ANY, DEPENDS ON HOW THE SEA FLOOR IS AFFECTED BY THE EARTHQUAKE, THE LOCATION OF ITS EPICENTRE AND ITS DISTANCE AWAY.
+WE ARE AGAIN FORTUNATE IN BEING RELATIVELY UNAFFECTED,+ MR. LAM SAID, THE STRONGEST EVER REACHING HERE BEING ONLY ABOUT ONE THIRD OF A METRE HIGH. THERE CAN BE NO REAL CAUSE FOR CONCERN IN HONG KONG.+
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