VAULT FOR RECORDING EARTHQUAKES FINISHED

Completion of construction work on the new Harvard seismology vault, excavation of which was begun last May, was announced yesterday by L. D. Leet, instructor in Seismology. New instruments of the latest type for the recording of earthquake shocks have been ordered and will be installed as soon as they are manufactured, with actual recording beginning about May 10. The completed vault will be one of the most perfect seismological stations in existence, according to Leet.

The Station consists of an excavation in solid rock 22 feet square, with the floor 15 feet beneath the earth's surface and the roof covered with six feet of rock and gravel. It is completely lined with concrete walls two feet thick, and the delicate recording instrument will be placed on concrete piers 30 Inches high, and five feet wide. This insulation will insure almost perfect recording of earthquakes, as the station will be entirely free from traffic disturbances, temperature changes, and all other interference.

The vault is placed on property adjacent to the new Harvard Astronomical Observatory. It has no superstructure, the only visible part being a skylight over a small workshop next to the vault, in which instruments not susceptible to shocks will be placed. The cell in which the seismographs will be installed will never be entered except to change the recording materials and adjust the machinery. Six seismographs will be used, two to record vertical movements of the earth, and four to record horizontal movements. Two of the later are already made, and are in use in the present seismographic station in the basement of the Geological Museum on Oxford Street. That station will be used for instruction of students after the new one is completed, with the Oak Ridge plant being devoted to research exclusively. The present equipment has proved inadequate for accurate recording of earth shocks, being so insufficiently insulated from outside disturbances that people walking on the stairs of the Museum produce an effect similar to a good-sized earthquake on its chart. The new station will increase recording accuracy about 100 per cent.

The four essentials of a good seismographic station, according to Leet, are isolation from traffic, large size, deep burial, and surrounding rock. In each of these respects the Harvard station is probably unsurpassed by any of the 250 seismographic stations in the world, of which about 30 are on the North American continent. The station here is the only one in New England, the nearest being in Ottawa, Canada, and New York City. Burial in solid rock is relatively unique.

The Harvard station will be able to record practically every earth shock of any force occurring anywhere on the earth, and will not only give the time of the quake but its precise location. Although destructive earthquakes are relatively infrequent, there being approximately 100 every year, slight quivering of the earth's surface are being recorded constantly