Some Engineering Problems Of The Panama Canal In Their Relation To Geology And Topography

EARTHQUAKES AS AN ELEMENT OF DANGER. elusion is quite in accordance with the observations set forth in along and fairly complete record“ of the earthquakes that have occurred from the time of the Spanish conquest to the year 1886. In all that time only two severe shocks were noted; one of these, in. 1621, destroyed many of the buildings in Panama, and one in 1882 damaged several buildings and bridges, and, locally, threw the rail- way track out of alignment. In Colon the latter quake is said to have opened a few crevices and to have been attended with some fatalities. Many smaller shocks have occurred and since the instal- lation of seismographs by the Isthmian Canal Commission numerous tremors, most of which are detectable only by the instrument, are recorded every month. At one time it was thought that the canal was liable to injury or destructions from earthquakes, but the fact is that no earthquake since 1621 would have seriously damaged it, and the shock of that year, though severe enough to shake down adobe houses, and even some masonry structures, would have had no serious effect on canal slopes and little effect on such rock-founded concrete structures as the locks. In support of this assertion the relatively little effect of the San Francisco earthquake on the now steel reinforced concrete buildings may be cited; and, of course, the locks are more solid than any building. On October 1, 1913, a fairly severe earthquake shock was felt on the Canal Zone. Its local intensity was estimated at V or VI on the Rossi-Forrell scale, which runs from I to X. In spite of the fact that some of the people were alarmed by the shaking of the houses, the quake had not the slightest effect on any part of the canal. A second shock, only slightly less intense, was felt on October 23, and this likewise failed to disturb even the most delicate adjustment of the lock machinery. Both these shocks were much heavier 100 miles southwest of Panama City than they were within the Canal Zone. Though it is not impossible that a destructive earthquake might visit the canal, still it is extremely improbable. In summary, then, the following arc the chief reasons why it is believed the canal will never be in any appreciable danger from earthquakes: 1. The large number of tremors detected every month by the recording instruments is evidence that slow adjustments are con- stantly taking place and thus that no great accumulations of stress that might later culminate in a big shock are probable. 2. The absence from the Isthmus region, of high mountains and of geologically recent volcanic activity is evidence in favor of the prob- able absence of earthquakes, especially as such high mountains are a striking geologic feature of the whole Central American earthquake belt. 3. The presence of numerous small faults and of the faulted con- ditions of such volcanic cores as Gold Hill and Contractors Hill is a De Ballore, F. de M., Tremblements de terre et eruptions. Volcaniques au Centre-Amerique. Soc. des Sciences Naturelles de Saone-et-Loir. 1888, p. 61.