

Minimizing Earthquake Damage 



About 10,000 people a year die as 

 a consequence of earthquakes. Most 

 of them live in underdeveloped parts 

 of the world, where housing is not 

 well constructed; indeed, the United 

 States and Canada may be among the 

 few places in the earthquake zones of 

 the world where building construction 

 is even slightly seismo-resistant, be- 

 cause reinforcing steel is used in 

 public buildings and wood framing 

 in private residences in the seismic 

 zones. 



Much more needs to be done, how- 

 ever. Structural engineers can now 

 determine the response of a building 

 to a given excitation with reasonable 

 accuracy. The basic problem remains 

 that of knowing what the ground 

 motion will be in a large earthquake, 

 so that appropriate building standards 

 can be established. Some measure- 

 ments of ground motion in earth- 

 quakes of intermediate size are avail- 

 able, but there are no good records 

 for large shocks. In California, the 

 next great shock may cause property 

 damage amounting to billions of dol- 

 lars. Loss of life may well be in the 

 thousands. Some of this hazard can 

 be reduced if appropriate changes in 

 the building codes for new con- 

 struction are made with the aim of 

 minimizing casualty from great earth- 

 quakes. 



Until now, there has been severe 

 disregard of the earthquake hazard. 



Tracts of homes are built within a 

 few feet of the trace of the 1906 San 

 Francisco earthquake, for example. 

 This section of the fault has remained 

 locked since l q 06, but some creep 

 has recently been observed. Accelera- 

 tion of the creep could imply a sig- 

 nificant hazard in an important urban 

 area. 



"Man-Made" Earthquakes 



Some natural earthquakes have 

 been triggered by man. The trigger- 

 ing agents have included underground 

 nuclear explosions, the filling of dam 

 reservoirs, and the injection of water 

 into porous strata. In all cases, the 

 earthquakes occurred near the trigger- 

 ing agent. In all cases, the energy re- 

 leased in the earthquake was already 

 stored in the ground from natural 

 sources. 



The water-injection case that oc- 

 curred near Denver, Colorado, is of 

 considerable interest. In that case, it 

 can be surmised that the water in- 

 jected into a shallow well at the Rocky 

 Mountain Arsenal between 1962 and 

 1965 lowered the friction on a pre- 

 existing fault and allowed a series of 

 earthquakes to be initiated. The oc- 

 currence of shocks was correlated to 

 the pumping history in the well. They 

 showed an increasing migration with 

 time and an increasing distance from 

 the well — all this in a region with no 

 previous history of earthquakes. In 



this case, the water seen 



acted as a lubricant to reduce 



tion. The migration of the shocks 



was due to stress propagation by 



concentrations at ends of ruptured 



segments. 



Can Great Earthquakes be 

 Prevented? 



Although these earthquakes were 

 triggered by man in his usual way of 

 modifying the environment without 

 thought for the consequences, the 

 experience in Colorado prompts an 

 interesting speculation. Suppose, for 

 example, one were to envision the 

 following situation some years from 

 now: Pumping stations are located 

 astride all the major earthquake zones 

 of the world. They serve to raise the 

 water pressure on the fault surfaces 

 several kilometers below the surface, 

 thereby reducing the friction. The 

 large plates are thus lubricated and, 

 without the friction at their edges, 

 they move at faster rates than at pres- 

 ent, releasing the accumulated stress 

 in a series of small, harmless earth- 

 quakes and avoiding the human toll of 

 destructive, catastrophic earthquakes. 



There are many years of research 

 between the first bit of serendipity at 

 Denver and this fantasy, however. In 

 the meantime, work on the prediction 

 problem must go ahead until the solu- 

 tion to the prevention problem makes 

 prediction gladly meaningless. 



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