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.. •. : , Page~Two January 12, 1981 Sadler House inatrumentational scales such as the Richter scale or to determine the intensity of an earthquake when no instruments- tional records are available. A Mercali IV earthquake is roughly equivalent to a Richter 3.0 to 3.5 earthquake. A Mercali IV earthquake would be expected to generate ground accelerations between 50 mm/sec./sec.' to 100 mm/sec./sec „ or 0.005 to 0.01 times the acceleration of gravity. .The effect of construction equipment operating upon alluvium is to inyluce round vibrations which are similar to the seismic waves produced by an•earthquake. The ground waves vary in amplitude and wave length and travel through the ground strata.' The prin iple difference in this situation is that an earthquake lasts ~nly ~ few seconds whereas the ground vibrations caused by construction equipment last for hours each day of operation. The approximate weight of the house including contents is estimated to be 46000 lbs. The force due to ground vibrations ( acceleration x weight _ gravity acceleration ) is calculated to be 210 lbs. to 420 lbs. This force generally is a horizontal, cyclical force. The cycle probably varies in length of time (.fractions of a second ). The long term repetitive occilating force caused by low ground 'accelerations is capable of causing damage to a house. Such damage would initially occur to walls, windows, loose appendages, etc. If the forces occur over a long period of time, the vibrations cold caluse 'fatigue stress of failures to connections, concrete a~ maso• y. If the underlying alluvium ie not at its optimum :density, settlement could occur which would induce further damage. Cracks occur in buildings because of many reasons. They usually occur within the first 5 years if they occur at a11, Unusual circumstances such as atypical weather or changing environmental conditions can cease cracks at a later age of the structure. CONCLUSION If there were no cracks prior to the equipment operation to the west of the houae,then the damage to the house, manifested by.numerous cracks, most likely occured because of the vibrations and vibrational forces induced by the construction equipment. If the"cracks were covered up by previous owners, then ground vibrations would be a possible, if not probable, cause of their reopening. At the present time, the integrity of the house is not impaired. However, additional ground vibrations which approximate the intensities described earlier in this report could cause additional damage such asi (1) more cracks; (2) loosening of windbws,ddors and cabinets; (3) cracking of the ~~ ~~