SEISMOLOGY. 367 



week of one or more (as many as three) components of seismic vibration, all 

 upon the same recording strip. Used with the torsion seismometers, these 

 assemblies are intended primarily for routine recording of seismic acceleration 

 (or intensity) at subordinate stations; but, in view of the simplicity and pre- 

 cision of the torsion seismometers, they will serve admirably in exploratory 

 work or tests of the suitability of sites proposed for primary or secondary 

 seismologic stations. Also, these will be useful in experimental field and 

 laboratory studies. For this, within limits, these recorders may be speeded 

 up to run at any desired rate. Moreover, they may be made to run very 

 slowly to serve in recording long-period earth tilts." 



With these first instruments more than one hundred local shocks were 

 recorded between February and September (1923), and the great Japanese 

 earthquake of September 1 left a very clear record, even though the instru- 

 ments were not appropriately " tuned " to record distant shocks most effect- 

 ively. It is of inestimable advantage to the future of seismology in all 

 fields of activity (1) that these instruments may be varied in period to suit 

 the particular group of vibrations which it is desired to study, or (2) several 

 sets of instruments of different period may be maintained at the same sta- 

 tion without becoming a serious burden. 



6. Recommendations. 

 The early and remarkable success attained in the development of suitable 

 instruments for the study of regional seismology has placed the committee 

 in position to recommend the immediate estabhshment of the first group of 

 stations and the systematic study of local earth tremors in southern Cali- 

 fornia. Studies of local faulting in this part of the State, which have been 

 carried on by Mr. Wood at intervals during the past two years, have pro- 

 vided the necessary information for selecting suitable sites and securing 

 an advantageous grouping of observing stations. He says (Annual Report, 

 1923) : 



"It is desirable that a chief station, with facilities for experimental and 

 development work as well as r6utine and research work, be established in the 

 neighborhood of Pasadena — most advantageously on the area of granite 

 which outcrops west of the city and the Arroyo Seco. A sound rock founda- 

 tion and freedom from traffic disturbances, combined with proximity to the 

 scientific resources of Pasadena and Los Angeles, unite in support of the 

 desirability of this location. 



"Then, for the first trial network of auxiliary stations — which may be 

 modified if experience suggests it — stations equipped with three component 

 assemblies of seismometric apparatus are recommended at Riverside, at 

 Fallbrook in San Diego County (or, failing that, at some point not now desig- 

 nated specifically in the southeastern part of Orange County), and, if prac- 

 ticable, on the island of Catalina. 



"The localities mentioned are favored provisionally on account of their 

 geographic position and distribution with reference to one another and to the 

 geologic faults most suspected of local seismic activity, and because of the 

 crystalline or other well-consolidated rock to be found at or near the surface." 



The Advisory Committee accordingly recommends to the President and 

 Trustees of the Institution : 



(1) Early provision for the equipment of a minimum group of provisional 

 stations, in locations to be approved by the committee and fully equipped 

 for the experimental study of regional seismology in southern Californa. 



