catalogo de terremotos para america del sur catalog of earthquakes ...

136
done usually with the curves and tables prepared at the UniversiLv of Saint
Louis (Saint Louis, Mo.) by the Rev. Joseph S. Jol iat, S.j. (Tentative Tables
of Travel Times for Near InrtI qu;kes, Saint L.ouis University, 1931); the tables
of .Jeffreys-bullen or !errin are used only in special cases. For all
events, he they historical or instrumental , the depths nrc not calculated.
For the instru"nLal casps, proce;o! bv tie omputer procrm Hypo 71, modi­
fied, the depti is calcn ated, taki 40 km as a reference depth, with an R
to indicate the Limitation due to) the pro;:nm.
0) lintensit i.; and matnitides
All of the cases of eartlthquakes processd by F. Ramirez or under hisdirection
(R - I), hisLtorical as well as instrumental, have magnitudes and intensities
a,i.ned. Neverthpl,,ss, the method used for the determination and
preci'e meaning, of ithe valuts is not known exactly; however, we believewith
some curtAintv th:Nt intens ities are evalimited in accordance with the ercall
M-odified :ca] lndthat rhe mnrnitlles are based on rto formula of Cutenberg
-Richter fo shallow l .' narthtqui; ker; of aI lifornia: M - I 1 1 1 or on the La­
bles ef eqtt ' lnr, whilch hay, bee n calcl ated f rom Lhs orl-Illa (Richter,
EIolmentnar So ism loit., p. 353, or !i o, Introduct ion to Sei.sn]ogy p. 117,
,
tabl.e 7). For Lhe hislorical onrthqtakes, the intensity was thus determined
by the uffec_. vnInated accotrding, to the datLa in the sources aind then the
magnitude ( I) was calclated; in the case of -nstrumental earthquakes, the
satm or tLhe inverse process was followed. For earthquakes for which those
values have nLt I e dot ermiied by the autlhrs of the other parameters, the
same prot'edure way usied
Naturall.', in tlse cas.s it, is not possible to stipulate the quality
or the dgree of p~rec'ision of the vilues assigned and therefore the values
must b taken with ct't ion; further ovaln tin and homogenization is needed.
This work has. vet to he done for tipdating the SISRA catalogue; therefore,the
intensitiesr for aerthqiialo processed during this stage of SISRA have net
been dertrminc~d. With Iret' l to LAP nn', 0ittde. An at:tempt has been maile to
estimate man, it. le, for allIpossib le 0vn s, t;in the provi.sional formula
"
Nib = I 1,; -4 1,It )- ( .71, where A i; the half amplitude of the first cycle
of P', iKen Iromit t e ve rl i ;a I -;ho t per id olco ponent of t he Ben ioff
seismograph or from the SRuO recort;, co -t'ed for the movemenL of the
gruni; T is the' period otf lth, ipr'vio:m ivtle I) Lhe liypocen r;il dLstance
to the sttiiotn, in kilm eters. Altltouigl the resiIts thus obtained have not
Leon fully atlvn'd, htv etca; t:ionalI compari son with va liues given by internationo]
centers, it can lie satttd t haL. tlecv aplpear to le rather low; there-fore
ae have not attemptv,,l to define the qual.lty.
o In t to a L' CaLIttm'tmo.
For the prep;ration t the CiLa lIog,11c of Intensities, it was agreed at
tle ho inning of tlte pro jt-t,, to uise tie model ,.:Iii.ch was adopted for project
SISAN and therefore (e l obtia incitrporat d in project SISRA all of the data
and results previons lv ohitaind. 'lhes wre :ncrear;.d and completed with
new data for events prp'v mool v anal vzei nod aIa rP' ittlmitor of new events
(138) wer, added to ti catal aIogi e. The' principal. srorce for this new data
was alsot tme wor" done by '. Ramirez, c.omplemented in many cases with information
and press report:s on file at: th, Instituto (;eofisico.