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•. Page~;Two • _ • January 12, 1981 Sadler House insCrumentational scales such as the Richter scale or to det+>.rmine the intensity of an earthquake when no instrumenta- tional records are available, A Mercall IV earthquake is roughly equ:Lvalent to a Richter 3,0 to 3.5 earthquake, A Mercali IV earthquake would be expected to generate ground accelerations bets,reea~50 mm/sec,/sec.`to 100 mm/sec,/sec „ or 0,005 to 0.01 times .the acceleration of g=avity. :i Tb.e effect of construction equipment operating upon a1lt~vium is to induce ground 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 principle difference in this situation is that an earthquake lasts only a 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 b~s 2I0 lbs. to 420 lbs. This force generally is a horizontal, cycLLcal force. The cycle probably varies in length of time ( fr+ictions of a second ). The long term repetitive occilating force caused by low grou:id '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 could cause fatigue stress of failures to connections, concx•ete and masonry. If the underlying alluvium is not at its optinntm:density, settlement could occur which would induce furtb.er damage. _. ,. !Cracks occur in buildings because of many reasons. They usually._occur within the first 5 gears if they occur at a11. Unusual.circumstances such as atypical weather or changing environmental conditions can curie cracks at a later age of the structure. CONCLUSIONi If there were no cracks prior to the equipment operation to the west of the house then the damage to the house, manifested by nwneroua cracks,: most likelq occured because of the vibrations and vibrational forces.i.nduced by the construction equipment, If th~a`crack.s were covered up by previous owners, then ground vibrations would be a.possible, if not probable, cause of their reope~sing. At the present time, the integrity of the house is not impaired. However, additional ground vibrations which appro~cimate the intensities described earlier in this re ort could cause additional damage such asi (1) more cracks; (2) loosening of window s, doors and cabinets; (3) cracking of the