Development of a Velocity Model for 

locating Aftershocks in the 

Sierra Pie de Palo Region of 

Western Argentina 

U.S. GEOLOGICAL SURVEY BULLETIN 1795 

Development of a Velocity Model for 

Locating Aftershocks in the 

Sierra Pie de Palo Region of 

Western Argentina 

By G. A. Bollinger and C. J. Langer 

Local extreme variations in sedimentary thickness required 

development of a velocity model to accurately compute 

hypocenters of the aftershock seismicity following the western 

Argentina (Caucete) earthquake of November 23, 1977. 

U.S. GEOLOGICAL SURVEY BULLETIN 1795 
DEPARTMENT OF THE INTERIOR 

DONAlD PAUl HODEl, Secretary 

U.S. GEOlOGICAl SURVEY 

Dallas l. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Bollinger, G. A. 

Development of a velocity model for locating aftershocks in 

the Sierra Pie de Palo region of western Argentina. 

(U.S. Geological Survey bulletin ; 1795) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1795 

1. Seismology-Argentina-Pie de Palo Mountains Region. 

I. Langer, C. j. II. Title. Ill. Series 

QE75.B9 no.1795 557.3s 87-600225 

[QE535.2A7] [551 .2' 2' 098263] 
CONTENTS 

Abstract 1 

Introduction 1 

Regional geologic setting 1 

Development of velocity model and travel time corrections 3 

Summary 12 

Acknowledgments 13 

References cited 13 

Appendix 14 

FIGURES 

1. Aftershock epicenter map 2 

2. Location map of study area 3 

3. Locations of refraction profiles 4 

4. Thickness of sedimentary rocks 6 

5. Average sedimentary rock velocities 7 

6. Uppermost Precambrian rock velocities 8 

7. Grid map for velocities and thickness 9 

8. Sedimentary rock travel times 10 

9. Wadati diagram 12 

TABLES 

1. P-wave velocity model, Sierra Pie de Palo region of Western Argentina 11 

2. Velocity model (AVM) station corrections, Tc, Argentina aftershock network 11 

3. Station-delay corrections, Td, Argentina aftershock network 12 

4. Final station corrections, Ts, Argentina aftershock network 12 

Contents Ill 

Development of a Velocity Model for Locating 

Aftershocks in the Sierra Pie de Palo Region of 

Western Argentina 

By G. A. Bollinger1 and C. j. Langer 

Abstract 

The ten stations included in a temporary seismograph 

network for locating aftershocks of the November 23, 1977, 

western Argentina earthquake were sited where the underlying 

sedimentary rock columns had thicknesses ranging from 0 to 

6 km (up to 1.5-sec variation in vertical one-way travel times 

for the P-waves). Such rapid changes in the velocity structure 

cause considerable difficulty in obtaining accurate hypocenter 

locations. Fortunately, velocity data were available in the form 

of 26 refraction profiles for the near surface (0-6+ km). Those 

profiles gave the velocities for the sedimentary column and the 

underlying Precambrian basement in the network area. An 

estimate of the regional crustal velocity structure for this 

geologically complex area had also been determined previously 

by analysis of data from a well-located nearby earthquake. 

Unpublished surface-wave studies extend the model to the 

upper mantle. This paper describes the use of the available data 

to refine the velocity estimates for the uppermost layers of the 

regional crustal velocity model and the method used to 

calculate P-wave travel time corrections for each station. The 

resulting model and station corrections were used, with good 

results, to locate the 185 aftershocks listed in the appendix. 

Average HYP071 error measures for the aftershock 

hypocenters were: RMS=0.12 sec, ERH=0.7 km, ERZ= 1.3 km. 

INTRODUCTION 

The epicentral region for the magnitude 7.3 (M5

) 

western Argentina (Caucete) earthquake of November 23, 

1977, and its aftershocks is restricted primarily to the 

eastern half of the Sierra Pie de Palo and to the eastern 

adjoining Valle Bermejo (fig. 1). That area lies within the 

Sierras de las Pampeanas (fig. 2) and is associated with 

the Sierras Pampeanas Occidentales geologic province, 

1 USGS and Virginia Polytechnic Inst. and State University, 

Blacksburg, Virginia 24061. 

a region of considerable stratigraphic and structural 

complexity (e.g., see Allmendinger and others, 1983; 

INPRES, 1977; Bastias and Weidmann, 1983; Jordan and 

others, 1983). The resulting velocity structure varies 

rapidly in both the horizontal and vertical directions; 

consequently, the area poses serious problems to accurate 

earthquake hypocentrallocations. 

The following discussion presents a brief summary 

of the regional geology of the aftershock zone followed 

by a detailed description of a four-stage procedure used 

to construct a local velocity model for the aftershock 

locale. Development of individual station corrections to 

account for systematic travel time differences at each of 

the seismograph locations completed the velocity model 

study. 

REGIONAL GEOLOGIC SETTING 

The Sierra Pie de Palo is encircled by a system of 

broad valleys (Vaile del Bermejo to the east and Vaile 

de Tulum to the south and west) that form a doughnutshaped basin (elevation of 500-700 m) filled in places with 

several kilometers of Quaternary age sediments. The 

eastern neighboring mountains, Sierra de Ia Huerta and 

Sierra de Valle Fertil as well as the central Sierra Pie de 

Palo, are composed of Precambrian and lower Paleozoic 

metamorphic and intrusive rocks that rise to more than 

3,000 m above sea level. The mountain fronts are 

generally bounded by northerly or north-northweststriking reverse faults that dip moderately to the east 

(Jordan and others, 1983; Bastias and Weidmann, 1983) 

but a set of crosscutting, east-northeast-trending faults 

and lineaments are also present (INPRES, 1977, p. 13). 

West of the Sierra Pie de Palo are the Paleozoic highlands 

that form the Andean Precordillera Centro Occidental 

with elevations locally in excess of 4,000 m. Reverse faulting here is extensive along both east- and west-dipping 

Regional Geologic Setting 
68° 

\ 

\ 

• -1 

A' 

Figure 1. Aftershock epicenter (open circles) map after Langer and Bollinger (1987). Foreshock epicenter (five-pointed star) 

and main shock epicenter (solid six-pointed star) are from Kadinsky-Cade and others (1985); station locations shown by open 

triangles with center dot and three-letter station codes. Intermediate depth earthquake epicenters indicated by solid dots. Note 

that two of these deeper events are off the west side of the figure. Faults, shown by heavy solid (confirmed) or dashed (inferred) 

lines with hachures on down-dropped sides, and Precambrian outcrop on the Sierra Pie de Palo, shown by pattern symbols, 

were taken from INPRES (1977) geologic map. Cities and villages are indicated by open square symbols and names. 

2 Velocity Model for Locating Aftershocks, Argentina 
40° 

DE LAS 

PAMPAENAS 

Figure 2. Location map of study area (rectangle) showing 

some of the geologic provinces of western Argentina. Irregularly 

shaped patterned figures are Sierras de las Pampaenas. The map 

is modified from Jordan and others (1983). 

faults that predominantly strike north-south, subparallel 

to the Andean front. Bastias and Wiedmann (1983) have 

examined and described some of the major faults both 

east and west of Sierra Pie de Palo and have documented 

evidence for Holocene movement on several of the fault 

scarps. Baldis and Febrer (1983) have suggested that the 

north-northwest-striking faults just east of the Sierra Pie 

de Palo and the east-northeast crosscutting faults through 

the Sierra Pie de Palo (fig. 1) represent intersecting 

megafault systems that have been active from early 

Precambrian time to present. 

DEVELOPMENT OF VELOCITY MODEL AND 

TRAVEL TIME CORRECTIONS 

The network of eight portable and two permanent 

stations used to record the aftershock activity of the 

November 23, 1977, earthquake resulted in five stations 

being sited on Precambrian rocks (CFA, VIC, MAY, 

CHU, and SNO) and five stations on the basinal alluvium 

(MOO, BRR, SAM, VIL, and SAJ; e.g., see fig. 3). 

Given these very different station bedrock types, fortunately an approximate regional P-wave crustal-velocity 

model (V olponi, 1968) and results from 26 refraction profiles in the epicentral area were made available by Yacimientos Petroliferos Fiscales (YPF), the Argentine 

National Oil Company (see fig. 3). All but one of the YPF 

profiles were reversed and provided data to compute the 

sedimentary column and uppermost Precambrian (basement) velocities. Additionally, sonic log data from two 

wells that had been drilled in the northern part of the 

study area near 30°S., 68°W. (D. R. Toland, Cities Service Company, Houston, Tex., personal commun., 1978; 

fig. 3) agreed, generally, with the refraction velocity data 

in their vicinity. However, the wells were not drilled deep 

enough to extend our knowledge of the Precambrian 

velocities and, thus, only helped to confirm the velocity 

information within the section. Also, depth to the top 

of the mantle (Mohorovicic discontinuity), and the upper mantle velocity were estimated by J. C. Castano (staff 

seismologist, INPRES, San Juan, Argentina, personal 

commun., 1977) based on unpublished surface-wave 

studies. 

To correct for the complexities in lithology and the 

other local geologic factors that affect seismic velocities, 

we state the following objectives and the analytic procedures to achieve these objectives: 

• Develop an "average" layered velocity model 

(A VM) that is representative of the upper 10 km of 

crust in the Sierra Pie de Palo area. 

• Estimate station corrections to account for 

systematic travel time differences at each station that 

result from the model. 

• Estimate "station-delay" corrections that account 

for systematic travel time differences at each station 

that result from unknown sources. 

• Combine the A VM station corrections with the 

"station-delay" corrections to estimate the "final" 

station corrections. 

A brief summary of what the available data include is: 

25 reversed and 1 non-reversed refraction profiles, well 

log data from 2 wells, a regional velocity model (V olponi, 

1968), depth to the upper mantle and upper mantle 

velocity estimates from Castano, and aftershock data 

recorded at 10 stations. Our task is to apply these data 

Development of Velocity Model and Travel Time Corrections 3 
® -9- I 69° 

-· aoo~r-0----~r---~~68~0~------------~ 

@r 

lMOG 

0\ 

-

.A.VIl 

-

SAM .A. 

0 10 20 30 '- 1 1 1 4p ~,o KILOMETERS 

I I 

4 Velocity M d o e I f or Locating Aftershocks, Argentina 
in a rational and also rigorous method to achieve the 

above-stated goals. A step-by-step description of how the 

''average velocity model'' was developed and how the station corrections were determined is given below. 

(1) Average velocity model (AVM), Upper 10 km 

(a) Location, length, and direction of profiles 

were plotted (fig. 3). 

(b) Thickness and average sedimentary-column 

velocities were determined for all profiles, 

plotted at the profile center, and contoured 

(figs. 4 and 5). 

(c) Precambrian basement velocities were 

determined, found to be variable, plotted, 

and contoured (fig. 6). 

(d) The study area was gridded at 1 I 4-degree 

intervals and, for each of the resulting 45 

grid points, the sedimentary velocity (V sed), 

sedimentary thickness (Zsed), and Precambrian basement velocity ( V pe), were 

estimated by interpolation between respective contours and then plotted (fig. 7). 

(e) Mean values were obtained directly for each 

of the parameters in figure 7 and used as 

representative numbers in the A VM. The 

generalized P-wave velocity model for the 

upper 10 km is then: 

P-wave 

Velocity 

(km/sec) 

2.87 

5.88 

Thickness 

(km) 

2.4 

7.6 

Depth to top of layer 

(km) 

0 

2.4 

Available measurements of middle and lower crustal 

velocities from Volponi (1968) add to our model and are 

as follows: 

P-wave 

Velocity Thickness Depth to top of layer 

(km/sec) (km) (km) 

6.2 22.0 10.0 

7.3 ? ? 

The combination of our AVM with Volponi's investigation (1968) and information from J. C. Castano leads to 

our final P-wave velocity model given in table 1. 

The model specifies only average velocities and 

thicknesses for the two layers above 10 km. However, 

looking at figures 4-8, considerable variability exists in 

sedimentary thickness, sedimentary velocity, and Precambrian velocity throughout the network area. Given the 

velocity and thickness for the A VM layers and, then, using figures 4, 5, and 6, to determine the "actual" P-wave 

travel time parameters for the upper two layers, we can 

estimate the AVM station corrections. 

(2) A VM Station Corrections, Tc 

(a) Determine vertical, one-way travel time 

through the upper 10 km which we call the 

"AVM travel time," Tm, according to 

values specified by the A VM. 

Tm=(2.4 km/2.87 km/sec)+(7.6 km/5.88 

km/sec) =0.84 sec+ 1.29 sec=2.13 sec 

(b) Use the "AVM travel time" (Tm=2.13 

sec) to contrast with the "actual station 

travel times," Ta, at each of the network 

stations. 

(c) Calculate difference between A VM and 

"actual" travel times for AVM station corrections: 

Sample A VM station correction calculations are given 

below for a basin location (MOO) and rock location 

(MAY). Because of adjustments in scale and projection 

that were necessary to composite the several large work 

maps used for preparation of the illustrations, corrections 

derived directly from the figures presented herein may 

not agree exactly with those described in the following 

text. 

Tc for MOG (Sedimentary Site) 

a. From figure 8, the sedimentary travel time, 

~ed= 1.8 sec 

b. From figure 3, the sedimentary thickness (including 

station elevation), zsed=6.2 km 

c. From figure 6, the Precambrian velocity, V pe = 6.0 

km/sec 

d. Thickness of Precambrian above 10 km, 

Zpe= 10.0-Zsed= 10.0 km-6.2=3.8 km 

Figure 3. (facing page) location of refraction profiles obtained from Yacimientos Petroliferas Fiscales (YPF) (Burna, Abel E., 

lng., Chief, Special Studies Agency of Interpretation and Investigation, YPF, Buenos Aires, Argentina, written commun., 1978); 

profiles are indicated by short lines with end bars; profile numbers given inside open circle symbols are those assigned by YPF. 

Seismograph station locations shown by solid triangles and 3-letter station codes. location of two wells indicated by dry-hole 

symbols (open circles with four tic marks). Precambrian outcrop areas shown by pattern symbol. Open area, except to the far 

west, represents basinal sediments. 

Development of Velocity Model and Travel Time Corrections 5 
Figure 4. Thicknesses of sedimentary rocks, as calculated from the refraction profile data (fig. 3), contoured in 

meters. Other symbols the same as in figure 3. 

6 Velocity Model for Locating Aftershocks, Argentina 
30o6~7-o------~----~~-6~8-o----------------~69o 

31° I I •3.72 

I 

\ 

\ 

' I 

I 

'>.~ ~~ 

32° 

3.0 

•2.25 

•3.30 

•3.32 

.&MOG 

•2.42 

0 

I 

~.371 

"-J e2.43 

10 20 30 40 

I I I 

SO KILOMETERS 

I 

Figure 5. Average sedimentary rock velocities, as calculated from the refraction profile data (fig. 3), contoured 

in km/sec. Other symbols the same as in figure 3. 

Development of Velocity Model and Travel Time Corrections 7 
aoo6~7-o _________________ s.a_o----------------~69o 

0 

I 

10 20 

I 

30 40 

I I 

50 KILOMETERS 

I 

Figure 6. Uppermost Precambrian rock velocities, as determined by the refraction profile data (fig. 3), contoured 

in km/sec. Other symbols the same as in figure 3. 

8 Velocity Model for Locating Aftershocks, Argentina 
aoo6~7-o _________________ 6~8-o----------------~69o 

3.90•4.9 

5.8 

3.90• 5.9 

5.6 

3.60. 4.2 

5.0 

3.20 • 3.0 

5. 5.Ji. 

Vll 

3.30 .& .1.8 

5.5 

SAJ 

3.40 • 0.3 

5.6 

3.10•1.0 

5.9 

EXPLANATION 

'Grid point 

Vsed Zsed 

vp€ 

MOG 

.& 

2.70 • 3.0 

6.2 

2.40 • 2.5 

6.1 

2.8o• 4.3 

6.1 

2.42 • 1.9 

6.2 

2.53 • 2.2 

6.1 

0 

I 

2.30.1.4 

5.8 

2.53 • 2.5 

5.8 

.& 

BRR 

-·-

2.54. 2.0 

5.8 

.&SAM 

2.52 • 2.2 

5.9 

10 20 30 40 

I I I 

50 KILOMETERS 

I 

Figure 7. Grid map for velocities (sedimentary rocks= V sed' Precambrian rocks= Vpe' both in km/sec) and sedimentary rock thicknesses (Zsed' in km), as derived from figures 4, 5, and 6. Other symbols same as in figure 3. 

Development of Velocity Model and Travel Time Corrections 9 
30o6~7-o _________________ s.a_o __________________ ago 

Figure 8. Sedimentary rock traveltimes (one-way vertical path), as calculated from the data shown in figures 4 and 

5, contoured in seconds. Other symbols the same as figure 3. 

10 Velocity Model for Locating Aftershocks, Argentina 
Table 1. P-wave velocity model, Sierra Pie de Palo region of 

western Argentina 

P-wave velocity Thickness Depth to top of layer 

(km/sec) (km) (km) 

2.87 2.~ 0 

5.88 7.6 2.~ 

6.2 22.0 10.0 

7.3 23.0 32.0 

8.1 half-space 55.0 

e. Precambrian travel time, T pe pe =Z IV pe =3.8 

kml6.0 kmlsec=0.63 sec 

f. ''Actual" one-way travel time, T =T d+T =1.80 a se pe 

sec+0.63 sec=2.43 sec 

g. Station correction, Tc= Tm-Ta=2.13 sec-2.43 

sec= -0.30 sec 

Tc for MAY (Rock Site) 

a. From figure 8, the sedimentary travel time, 

Tsed=O.O sec (station located on Precambrian 

rock) 

b. Sedimentary thickness, Zsed= 0.0 

c. From figure 6, the Precambrian velocity, 

vpe -6.0 kml sec 

d. Thickness of Precambrian above 10 km, T = pe 

10.0 km+station elevation= 10.0 km+0.71 

km= 10.71 km 

e. Precambrian travel time, T -Z IV = 10.71 pe pe pe 

kml6.0 kmlsec= 1.78 sec 

f. "Actual" one-way travel time, 

Ta= Tsed+ Tpe=O.O sec+ 1.78 sec= 1.78 sec 

g. Station correction, Tc= Tm-Ta=2.13 sec-1.78 

sec= +0.35 sec 

A listing of the corrections derived in a similar manner for all network stations is given in table 2. 

(3) Station-delay Corrections, Td 

The A VM station corrections almost certainly 

will not account for all of the travel time complexities within the region. Therefore, "station 

delay corrections," Td, determined from the 

travel time residuals will also be applied in this 

study. Those corrections were calculated using 

the following procedure: 

a. Select a 20-event subset from the entire sample of aftershocks of the 

November 23, 1977, Argentina earthquake that were recorded by the 

portable network. Those 20 events 

should be well recorded by all of the 

network stations and have epicenters 

that are well distributed throughout 

Table 2. Velocity model (AVM) station corrections, Tc, 

Argentina aftershock network 

Station 

BRR 

CFA 

CHU 

MAY 

MOG 

SAJ 

SAM 

SNO 

VIC 

VIL 

Site Lithology Tc correction 

(sec) 

Sedimentary +0.02 

pe rock +0.30 

do. +0. 32 

do. +0.35 

Sedimentary -0.30 

do. +0.03 

do. -0.09 

pe rock +0.30 

do. +0. 40 

Sedimentary -0.03 

the aftershock zone and have depths 

greater than 10 km. 

b. Locate the selected aftershocks using 

only the most precise arrival-time 

data available; that is, the P-wave arrival times from stations located on 

rock (CPA; VIC, MAY, CHU, and 

SNO) plus arrival-time data from 

VIL (for asimuthal control). Assume 

a PIS velocity ratio of 1. 73 and use 

S-wave arrival times as recorded by 

the short-period horizontal seismographs at CF A. Apply the A VM 

station corrections. Results of this 

location process demonstrated that 

significant travel time residuals still 

remained at some stations located on 

alluvium, particularly MOO, BRR, 

and SAM. Thus, averages of the 

travel time residuals were determined 

for the individual network stations to 

serve as preliminary delay corrections, Td. 

c. Relocate the 20 selected events using 

their above preliminary-delay corrections and the S-wave arrival times recorded at rock site stations and using 

the Wood-Anderson instruments in 

San Juan (SAJ). Try various PIS velocity ratios to establish a value that 

tends to minimize the S-wave 

residuals and construct a Wadati plot 

using only the P and S-wave arrival 

Development of Velocity Model and Travel Time Corrections 11 
• 

c. 

.... 

14 

Ts-Tp (sec) 

Figure 9. Wadati plot showing traveltimes of 5-wave minus 

traveltimes of P-wave (Ts-Tp, sec) versus traveltime of P-wave 

(Tp, sec) for 20-event subset (refer to page 20). Data from the 

rock site stations. 

times recorded at the rock sites (fig. 9). The 

result of both the PIS velocity ratio search 

and the Wadati plot was the selection of a 

value of 1. 70. 

d. To arrive at the final station delay corrections, Td, relocate the 20-event subset of 

aftershocks using the 1. 70 PIS velocity ratio 

and average the travel time residuals at each 

of the 10 stations. Table 3 presents the 

results of this procedure for the study area. 

(4) Final Station Corrections, Ts 

Obtain the algebraic sum of the A VM station corrections, Tc, and the "station delay" corrections, 

Td, to estimate the "final" station corrections, T5 , 

as listed in table 4. 

SUMMARY 

The velocity model described in table 1 and the 

station corrections listed in table 4 were used in the 

HYP071 program to locate the aftershocks of the western 

12 Velocity Model for Locating Aftershocks, Argentina 

Table 3. Station-delay corrections, Td Argentina 

aftershock network 

Station Site Lithology Td Correction 

(sec) 

BRR Sedimentary -0.27 

CFA pe rock +0.17 

CHU do. o.oo 

MAY do. +0.14 

MOG Sedimentary -o.97 

SAJ do. o.oo 

SAM do. -0.39 

SNO pe rock o.oo 

VIC do. -0.01 

VIL Sedimentary +0.38 

Table 4. Final station corrections, T5 Argentina 

aftershock network 

Ts, Correction 

Station Site Lithology (sec) 

BRR Sedimentary -0.25 

CFA pe rock +0.47 

CHU do. +0.32 

MAY do. +0.49 

MOG Sedimentary -1.27 

SAJ do. +0.03 

SAM do. -0.48 

SNO pe rock +0.30 

VIC do. +0.39 

VIL Sedimentary +0.35 

Argentina earthquake of November 23, 1977 (Langer and 

Bollinger, 1987). The average HYP071 error measures 

for the aftershock hypocentral calculations were: 

RMS=0.12 sec; ERH=0.7 km; ERZ= 1.3 km. We do 

not have a way to check for the presence of any systematic 

biases, but the use of high-quality S-wave data from CF A 

and SAJ eliminates the possibility of gross mislocations. 

Additionally, the depth distribution of the hypocenters 

(near surface to 30+ km; 110-135 km) given by Langer 

and Bollinger is the same as that derived from special 

seismicity studies of the region (Barazangi and !sacks, 
1976). A full listing of the aftershock locational and error parameters is given in the appendix. 

ACKNOWLEDGMENTS 

Our appreciation is extended to the Instituto Nacional de Prevenci6n Sismica (INPRES) and all personnel who contributed to our field monitoring program. 

Director lng. Julio Aguirve Ruiz and staff seismologist, 

Dr. Juan C. Castano, provided assistance toward the 

necessary scientific and logistical support. We are also 

grateful to S. T. Algermissen for his coordination of this 

joint U.S.-Argentine postearthquake study. Ing. Abel E. 

Burna with YPF in Buenos Aires, Argentina, kindly provided the refraction profile data that were so important 

to our model development. Mr. David R. Toland of Cities 

Services Corporation, International Area, Houston, Tex., 

graciously provided the sonic logs for the two wells in 

the study area. 

We also express gratitude to J. P. Whitcomb and 

R. F. Henrisey for their fieldwork and to Martha Adams, 

whose careful efforts obtained the basic data from the 

seismograms. M. J. Cecil and A. M. Rogers critically 

reviewed the manuscript and provided many helpful comments and suggestions. 

REFERENCES CITED 

Allmendinger, R. W., Jordan, T. E., Palma, M., and !sacks, 

B. L., 1983, Paleogeography and Andean structural 

geometry, northwest Argentina: Tectonics, 2, p. 1-16. 

Baldis, B. A., and Febrer, J., 1983, Geodynamics of the Andean arc and related regions: in Geodynamics of the 

Eastern Pacific Region, Carribbean and Scotia Arcs, edited 

by Ramon Cabre, S. J., American Geophysical Union and 

Geological Society of America, Geodynamics Series, v. 9, 

p. 127-135. 

Barazangi, M., and !sacks, B., 1976, Spatial distribution of 

earthquakes and subduction of the Nazca plate beneath 

South America: Geology, v. 4, p. 686-692. 

Bastias, H. E., and Weidmann, N., 1983, Mapa de fallamiento moderno de Ia provincia de San Juan: Universidad Nacional de San Juan, Facultad de Ciencias Exactes, San 

Juan, Argentina, scale 1:500,000. 

INPRES (lnstituto Nacional de Prevenci6n Sismica), 1977, El 

terremoto de San Juan del23 de Noviembre de 1977, informe preliminar: Instituto Nacional de Prevenci6n 

Sismica, San Juan, Republica Argentina, 101 p. 

Jordan, T. E., !sacks, B. L., Allmendinger, R. W., Brewer, 

J. A., Ramos, V. A., and Ando, C. J., 1983, Andean tectonics related to geometry of subducted Nazca plate: 

Bulletin of the Geological Society of America, 94, 

p. 341-361. 

Kadinsky-Cade, Katherine, Reilinger, Robert and !sacks, Bryan, 

1985, Surface deformation associated with the November 

23, 1977, Caucete Argentina earthquake sequence: Journal of Geophysical Research, v. 90, p. 12,691-12,700. 

Langer, C. J., and Bollinger, G. A., 1988, Aftershocks of the 

western Argentina (Caucete) earthquake of 23 November 

1977-some tectonic implications: Tectono-physics (in 

press). 

Lee, W. H. K., Bennett, R. E. and Meagher, K. L., 1972, A 

method of estimating magnitude of local earthquakes from 

signal duration: U.S. Geological Survey Open-File Report 

72-223, 28p. 

Volponi, F. S., 1968, Los terremotos de Mendoza del 21 de 

Octubre de 1968 y Ia estructura de Ia corteza terrestre [The 

Mendoza earthquakes of 21 October 1968 and the structure of the earth's crust]: Acta Cuyana de lngenieria, 

v. XII, Instituto Sismologico Zonda, Facultad de Ingenieria, Universidad Nacional de Cuyo, San Juan, Argentina, p. 95-110. 

References Cited 13 
APPENDIX 

List of aftershocks for the Argentina earthquake of November 23, 1977 

~ 

1 2 3 Standard errors 5 Date Origin Lat. s Long. W Depth No. DMIN RMS DLAT DLON DZ QF MD 

(Dec. 1977) (UTC) (deg) (deg) (km) obs. (km) (km) (km) (km) 

06 1705 06.54 31.270 67.978 29.2 13 45 0.09 .24 0.22 0.66 B 4.7 

06 1827 39.00 31 .310 67.847 24.3 11 49 0.10 .43 .31 2.35 c 4.3 

06 1932 27.99 31.285 67.953 28.5 12 45 0.13 .45 .38 .73 B 3.5 

06 2336 32.45 31.265 67.969 27.3 10 46 0.08 .25 .33 .95 8 3.7 

07 0200 32.82 31.140 67.737 7.5 11 47 0.08 .30 .51 2.01 c 3.6 

07 0322 41.52 31.276 67.956 27.8 11 46 0.18 .56 .62 1. 71 B 4.4 

07 0409 55.42 31.576 67.529 13.1 12 19 0.15 .45 .57 1.80 8 3.3 

07 0554 18.64 31.746 68.027 115.1 12 6 0.11 .78 .91 1.35 c 2.6 

07 0655 46.13 31.694 67.939 30.0 11 5 0.10 .61 .37 .60 A 3.2 

07 0802 19.84 31.837 67.836 17.7 10 16 0.08 .28 .35 .84 B 3.0 

07 0807 09.89 31.038 67.803 2.4 13 53 0.12 .24 .29 .42 c 4.0 

07 0817 29.49 31.827 67.737 17.1 10 24 0.07 .21 .25 1.01 8 4.1 

07 0919 04.14 31.508 67.537 52.1 12 19 0.10 .35 .43 .95 A 2.5 

07 0926 12.35 31.252 67.971 22.4 12 47 0.08 .24 .22 1.75 8 2.8 

07 0941 45.25 31.297 67.966 26.8 14 43 0.12 .34 .29 .83 B 3.9 

07 1130 27.97 31.837 67.743 8.9 11 24 0.09 .31 .28 .81 8 2.7 

07 1413 06.22 31.456 67.468 19.9 11 15 0.17 .65 .95 2.50 B 2.4 

07 1431 13.52 31.128 67.881 21.6 11 60 0.16 .50 .40 3.74 c 3.4 

07 1509 39.03 31.276 67.833 21.3 11 53 0.08 .27 .28 2.17 c 3.2 

07 1612 45.01 31.062 67.867 9.7 12 58 0.09 .25 .23 2.48 c 2.6 

07 1705 40.21 31.580 67.734 31.1 11 28 0.15 .55 .52 .51 8 3.2 

07 1720 12.82 31.822 67.808 15.0 13 18 0.14 .32 .34 1.37 B 3.1 

07 1823 48.02 31.683 67.889 30.1 11 9 0.13 .66 .66 .74 A 2.8 

07 1835 12.65 31.114 67.798 7.8 14 52 0.08 .16 .19 .75 c 2.7 

07 2012 27.47 31.640 67.913 28.5 11 12 0.08 .36 .24 .49 A 2.9 

07 2016 14.10 31.780 67.803 22.4 12 16 0.09 .25 .25 .57 8 3.1 

07 2029 13.52 31.509 67.869 22.4 11 27 0.11 .46 .32 1.47 B 3.2 

07 2033 27.85 31 .269 67.845 9.5 10 53 0.13 .46 .46 4.02 c 2.8 

07 2137 16.22 31.043 67.782 4.4 12 51 0.10 .23 .22 3.63 c 3.2 

07 2252 29.34 31.792 67.833 21.3 11 14 0.15 .47 .47 .81 B 3.0 

08 0224 36.05 31.136 67.907 23.8 12 58 0.11 .29 .30 1.27 c 2.7 

08 0416 05.64 31.527 67.577 13.9 12 23 0.07 .23 .24 1.30 B 3.0 

08 0625 05.09 31.231 67.803 7.9 11 55 0.12 .38 .62 2.34 c 3.3 

08 1103 28.38 31 .800 67.854 24.0 11 13 0.10 .35 .42 .61 B 3.2 

08 1202 26.51 31.421 67.874 7.4 10 36 0.08 .44 .31 1. 79 B 3.2 

08 1251 44.76 31.679 67.891 28.3 11 10 0.16 .60 .60 .89 B 2.6 

08 1338 23.41 31.274 67.915 24.5 11 48 0.13 .47 .34 2.42 8 3.3 

08 1505 31 .44 31.077 67.853 23.8 11 58 0.11 .33 .33 1.45 c 3.2 

08 1734 21.13 31.260 67.832 2.3 10 55 0.13 .46 .31 .61 c 3.0 

08 1831 47.60 31.560 67.079 134.0 13 25 0.16 .85 1.32 1.26 c 2.7 

08 1834 51.93 31.285 67.966 25.8 12 44 0.08 .20 .19 .80 8 3.0 

08 1904 43.57 31 .458 68.022 28.2 10 26 0.08 .31 .21 .48 A 3.2 

08 1952 15.33 31.234 67.752 8.0 12 50 0.10 .22 .42 1.37 B 3.8 

08 2046 35.61 31.007 67.797 5.2 12 53 0.05 .12 .12 .67 c 2.5 

08 2321 28.35 31.051 67.795 19.5 13 52 0.09 .20 .30 2.89 c 2.1 

09 0038 07.40 31.451 67.979 31.9 12 30 .13 .49 .37 .48 A 3.3 

09 0102 28.70 31.382 67.803 8.0 11 42 0.13 .55 .33 1.52 8 3.3 

09 0131 59.19 31.197 67.845 1.6 12 58 0.18 .46 .43 .71 c 2.9 

09 0248 58.05 31.509 67.705 30.4 11 35 0.09 .32 .35 .38 8 3.3 

09 0511 31.44 31.146 67.722 2.6 12 45 0.06 .16 .14 2.08 c 2.7 

09 0716 54.56 31.058 68.003 1.7 13 49 0.14 .26 .29 .42 B 2.8 

09 0825 21.78 31.034 67.800 8.0 10 53 0.08 .23 .26 1.02 c 2.7 

09 0918 12.34 31.502 67.690 31.3 11 34 0.12 .50 .39 .45 B 3.0 

09 1036 03.65 31.777 67.969 10.8 12 4 0.06 .20 .15 .37 8 3.3 

09 1220 11.19 31.121 67.746 7.0 13 47 0.11 .30 .42 1.51 8 2.7 

09 1244 47.41 31.247 67.988 28.0 12 46 0.18 .49 .52 1.68 B 3.2 

09 1519 45.19 31.272 67.980 25.6 14 45 0.08 .20 .21 .76 8 3. 7 

09 1842 54.79 31.098 67.864 6.5 11 57 0.14 .46 .37 1.87 c 2.3 

09 1856 09.65 31.491 67.727 31.6 11 13 0.15 .79 .58 .72 A 2.7 

09 2032 27.03 30.988 67.875 9.2 13 52 0.15 .35 .38 2.94 c 3.1 

09 2057 52.90 31.303 67.968 27.6 13 42 0.12 .33 .32 1.01 B 2.9 

09 2144 48.19 31.615 67.839 12.8 15 18 0.11 .27 .24 .87 B 4.2 

09 2247 39.93 31.348 67.868 4.8 12 33 0.12 .42 .29 1. 93 B 3.8 

09 2310 48.66 31 .564 67.968 30.5 12 19 0.13 .75 .52 . 72 A 3.3 

14 Appendix 
List of aftershocks for the Argentina earthquake of November 23, 1977-Continued 

.. Standard errors 1 2 3 5 Date Origin Lat. S Long. W Depth No. LMIN RMS DLAT DLOO DZ QF MD 

(Dec. 1977) (UTC) (deg) (deg) (km) obs. (km) (km) (km) (km) 

10 0030 33.21 31.416 67.908 16.8 12 31 0.13 .49 .33 2.87 8 3.1 

10 0055 22.91 31.142 67.819 6.3 14 51 0.09 .21 .18 .91 c 3.0 

10 0140 25.74 31.057 68.012 6.2 14 49 0.06 .13 .19 .59 8 3.5 

10 0256 41.61 31.833 67.828 24.7 12 17 0.09 .29 -33 .63 8 3.2 

10 0413 19.42 31.526 67.758 28.5 12 13 0.09 .38 .25 .58 A 2.9 

10 0433 57.69 30.913 69.006 110.9 16 69 0.27 1.50 2.16 1.98 D 3.6 

10 0436 18.77 31.112 67.859 6.8 15 55 0.07 .14 .13 .47 c 3.1 

10 0519 38.23 31 .463 67.636 41.0 12 12 0.08 .48 .28 1.02 A 3.3 

10 0704 17.20 31.743 67.936 10.1 13 3 0.10 .32 .30 .30 8 3. 7 

10 0711 51.12 31 .225 67.690 25.9 15 39 0.12 .28 .32 1.27 8 4.1 

10 0719 20.84 31.135 67.771 23.1 12 50 0.10 .26 .29 1.26 8 3-3 

10 0836 56.29 31.261 67.708 25.4 12 35 0.08 .25 .28 1.42 8 4.2 

10 1010 29.48 31.097 67.938 22.8 14 56 0.08 .18 .18 1.07 c 3.5 

10 1016 12.99 31 .579 67.849 14.2 12 21 0.18 .78 .48 2.44 8 3.8 

10 1131 07.32 31.495 67.745 30.2 12 14 0.17 .67 .47 .74 8 2.8 

10 1250 13.21 31.741 67.968 27.2 10 0 0.17 .74 .70 .84 c 2.8 

10 1314 05.48 31.397 68.668 112.1 17 18 0.16 .77 1.07 1.01 c 3.2 

10 1419 54.63 31.249 67.735 27.7 13 37 0.12 .39 .42 1.89 8 4.0 

10 1446 29.23 31.250 67.726 20.9 13 37 0.06 .17 .21 1.39 8 3-3 

10 1448 06.24 31 .250 67.715 21.5 13 36 0.14 .43 .46 2.94 8 3.1 

10 1504 33.02 31.615 67.959 30.2 11 14 0.20 1.42 .96 1.24 8 2.3 

10 1839 07.73 31.126 67.917 23.2 14 56 0.13 .32 .32 1.67 c 3.7 

10 1926 04.85 31.856 67.705 16.4 10 28 0.24 .74 1.09 3.99 8 3.0 

10 1929 51 .89 31 -370 67.948 23.8 12 37 0.19 .84 .55 3.36 8 2.7 

10 2047 34.09 31.778 67.490 23.1 13 27 0.11 .31 .35 1.07 8 3-3 

10 2100 19.72 31 .058 67.951 6.4 11 52 0.09 .25 .22 ~96 c 3.5 

10 2158 07.95 31.758 67.680 26.8 12 21 0.10 .30 .29 .61 8 3.4 

10 2315 10.57 31 .229 67.740 19.9 13 39 0.09 .23 .28 2.16 8 3.6 

11 0044 25.34 31.163 67.814 8.4 13 48 0.12 .29 .27 1.51 8 3.8 

11 0327 12.73 31.038 67.802 6.2 13 53 0.09 .30 .25 1.36 c 3.3 

11 0447 31.72 31.645 68.200 48.1 13 6 0.16 .71 .84 1.80 c 2.2 

11 0452 55.89 31 .528 67.785 31.6 13 15 0.09 .46 .27 .37 A 2.7 

11 0531 53.92 31.076 67.940 5.8 14 55 0.09 .23 .22 .98 c 3-3 

11 0705 02.42 31.703 67.791 10.0 12 17 0.14 .40 .35 .77 8 3.4 

11 0707 08.36 31.151 67.728 16.7 13 46 0.06 .13 .23 2.24 c 3.1 

11 0758 17.41 31.271 68.757 116.1 16 28 0.19 1.06 1.25 1.44 c 2.4 11 0945 09.35 31.168 67.788 6.8 14 47 0.14 .29 .39 1.46 8 3.4 11 0950 36.56 31.833 67.788 11.7 9 20 0.13 .49 .60 3.01 c 2.6 11 0958 59.98 31.767 67.770 20.9 13 19 0.09 .27 .26 .65 8 3.2 11 1038 10.17 31.267 67.951 6.9 13 45 0.08 .24 .18 .73 8 3.0 11 1044 40.43 31 .173 67.776 16.5 14 46 0.07 .15 .20 2.50 c 3.4 11 1046 53.67 31.080 67.891 22.9 13 58 0.10 .28 .23 1.38 c 3.0 11 1102 12.24 31.140 67.985 25.9 11 51 0.13 .39 .40 1.55 8 3.3 11 1246 21.60 31.425 67.733 27.4 13 19 0.10 .50 .27 .73 8 2.4 11 1331 04.23 31 .479 67.655 34.2 12 10 0.11 .52 .43 1.04 A 2.9 11 1402 23.51 31.277 67.893 2.0 11 41 0.10 .28 .25 .42 8 3.0 11 1430 43.87 31 .366 67.728 14.1 15 24 0.15 .42 .33 3.66 8 3.0 11 1617 11.37 31.413 67.704 9.8 14 19 0.13 .37 .31 .96 8 2.9 11 1626 00.07 31.415 67.699 11.5 13 18 0.10 .30 .26 1.97 8 3.3 11 1640 44.21 31.505 67.781 28.6 12 16 0.13 .56 .36 .87 A 3-3 11 1643 19.07 31.418 67.709 9.7 13 18 0.11 .32 .28 .79 8 3.0 11 1745 50.14 31.828 67.761 21.3 13 22 0.09 .25 .29 .60 8 2.9 11 1857 57.32 31.520 67.867 13.2 13 23 0.19 .80 .44 3.82 8 3.6 11 1934 24.03 31.116 67.856 23.0 13 55 0.07 .18 • 17 .87 c 2.9 11 2121 55.83 31.538 67.730 31.1 12 10 0.13 .60 .46 .52 A 2.7 11 2128 13.25 31.084 67.816 8.7 13 54 0.09 .20 .24 1.80 c 2.6 11 2231 59.78 31 .553 67.634 31.3 12 2 0.13 .52 .46 .47 A 3.1 11 2300 56.10 31.075 67.995 22.1 14 51 0.09 .21 .21 1.21 c 2.8 11 2333 08.34 31 .359 67.697 28.6 11 24 0.20 1.00 .68 1.60 8 2.9 

12 0043 29.00 31.032 67.802 1.7 12 53 0.09 .23 .23 .50 c 3.8 12 0114 45.01 31.801 67.833 22.0 13 14 0.07 .20 .22 .37 8 3.6 12 0215 38.32 31.277 67.918 27.5 12 42 0.07 .21 .19 .65 8 3.5 12 0304 45.28 31.517 68.868 110.0 16 30 0.16 .93 1.46 .95 c 2.7 12 0412 45.04 31.266 67.986 26.3 12 45 o. 10 .28 .28 .94 8 2.7 12 0443 24.41 31 .503 67.730 30.6 12 12 0.05 .19 .18 .19 A 2.5 12 0556 13.62 31.353 67.835 20.6 13 31 0.12 .41 .32 2.58 8 3.1 12 0611 22.57 31 .466 67.666 8.8 12 12 0.16 .63 .48 1.32 8 3.3 12 0819 52.39 31.817 67.828 17.2 11 16 0.16 .48 .60 1.54 c 2.4 12 0916 14.94 31 .574 67.502 16.5 12 12 0.09 .28 .34 .86 8 2.9 12 1029 00.95 31.194 67.724 6.0 13 43 o. 14 .48 .48 2.14 c 2.8 

Appendix 15 
List of aftershocks for the Argentina earthquake of November 23, 1977-Continued 

.. Standard errors I 2 3 5 

Date Origin Lat. s Long. W Depth No. IX-fiN RMS DLAT DLOO DZ QF Mo 

(Dec. 1977) (UTC) (deg) (deg) (km) obs. (km) (km) (km) (km) 

12 121!4 21!.77 31.120 67.779 1.6 11J 50 0.11 .22 .28 .39 c 3.1 

12 131!2 1!2.09 31 .208 67.694 20.0 11 lJO 0.09 .31J .30 2.11! c 3.1 

12 131!6 00.55 31.119 67.766 2.5 12 1!9 0.08 .19 .19 2.89 c 2.9 

12 1510 01.99 31 .201 67.708 16.7 13 lJ1 0.13 .35 .1!2 3.80 c 3.2 

12 1517 1!8.25 31.392 67.864 20.9 12 30 0.18 .71 .lJ7 3.51 B 3.0 

12 1602 29.29 31 .208 67.708 20.8 11J lJ1 0.11! .39 .50 2.85 B 3.9 

12 1715 16.52 31.482 67.1!82 11!.7 11 15 0.09 .31 .33 1.01! A 2.5 

12 171!8 28.61! 31.198 67.698 15.7 12 42 0.08 .28 .32 2.78 c 2.9 

12 1908 36.22 31.209 67.701 21!.3 12 lJ1 0.16 .50 .56 3.15 B 2.1J 

12 201!4 16.60 31.21!6 67.767 23.1J 12 38 0.13 .1!5 .38 3.79 B 2.7 

12 2056 32.39 31.577 67.720 30.8 13 9 0.09 .21J .28 .25 A 3.2 

12 2307 10.58 31.566 67.922 7.0 12 19 0.17 .58 .51 1.93 c 3.2 

12 2318 23.11 31.81!6 67.892 19.3 13 11J 0.09 .29 .28 .73 B 3.7 

12 2331 51 .71J 31 .1!70 67.736 30.7 12 15 0.08 .38 .32 .40 A 3.0 

13 0033 09.95 31.571! 67.673 5.3 11J lj 0.13 .50 .36 1.10 B 3.1 

13 0220 57.35 31 .268 67.708 26.9 11J 31J 0.11! .32 .35 1.07 B 2.8 

13 0301! 36.21 31.385 67.702 30.3 13 21 0.09 .33 .27 .1!2 A 2.8 

13 0341 55.31 31 .222 67.753 5.7 11J lJO 0.10 .32 .26 1.30 B 2.9 

13 071JlJ 12.1JlJ 31.866 67.81!9 18.0 12 18 0.09 .28 .31 .87 B 3.5 

13 0802 11.80 31.559 67.61!1 31!.6 12 1 0.12 .lJ7 .lJlJ .86 A 3.1 

13 081!5 1!0.12 31.519 67.608 31!.6 13 6 0.15 .60 .53 .99 A 2.3 

13 1006 17.79 31 .699 67.523 23.2 11J 18 0.13 .35 .39 .65 B 1!.3 

13 1100 26.53 31.785 67.811 9.3 11 16 0.12 .33 .1!6 .98 B 2.7 

13 11!24 01!.99 31 .121! 67.830 7.0 13 53 0.12 .28 .31J 1.51! c 3.8 

13 1552 50.28 31.355 67.862 23.0 12 32 0.15 .55 .39 2.75 B 3.7 

13 1620 26.83 31.231 67.772 15.2 13 lJO o. 10 .29 .28 3.90 c 3.6 

13 1722 51!.94 31.709 67.507 16.9 13 20 0.07 .20 .19 .71J B 2.7 

13 1845 1!5.76 31.757 67.771! 21.6 11 18 0.13 .1!1 .36 .77 B 2.7 

13 1851 1!5.73 31.570 67.861 12.0 12 21 0.13 .50 .29 2.18 B 3.1J 

13 1904 15.08 31 .666 67.738 23.8 12 15 0.15 .52 .42 .85 B 2.5 

13 1919 21 .58 31.773 67.795 24.5 13 17 0.09 .26 .26 .52 B 2.8 

13 2325 51!.29 31.652 67.591 11.0 12 10 0.06 .18 .16 .81 B 3.5 

14 0230 35.57 31.811 67.835 22.8 12 15 0.13 .42 .1!1 .79 B 2.9 

11J 031JlJ 53.99 31 .673 68.01JlJ 30.7 12 10 0.15 .85 .65 .59 c 2.4 

14 0352 lJ2.2lJ 31.61!5 67.750 13.7 11 11J 0.10 .30 .26 1.01! B 2.2 

14 1121! 30.31 31.139 67.911 22.6 15 55 0.09 .19 .21 1.12 c 3.2 

14 11J01J 11.65 31.713 67.869 29.9 12 10 0.17 .66 .57 .71J B 2.4 

11J 171!2 55.11 31.111 67.767 8.1 12 1!9 0.07 .18 .22 .86 B 3.1 

14 2217 08.00 31 .637 69.029 116.1 16 46 0.16 1.32 1.32 1.13 c 2.9 

15 01!17 25.16 31 .585 67.727 29.2 14 9 0.13 .39 .36 .55 A 3.0 

15 01!36 33.23 31.132 67.911 8.1J 13 55 0.07 .17 .17 1.1!1 c 3.0 

15 0724 57.89 31.316 67.902 27.0 15 38 0.11 .28 .26 .88 B 3.8 

15 0751 21.62 31.838 67.831 13.2 15 17 0.11 .26 .28 1.15 B 3.5 

15 0803 38.56 31 .1!93 68.722 122.2 18 16 o. 16 .86 1.15 .97 c 2.8 

15 0958 24.94 31.122 67.837 6.6 11J 53 0.08 .16 .16 .59 c 3.7 

15 1031! 02.60 31 .099 67.894 22.5 11J 58 0.08 .17 .19 .93 c 2.9 

15 11!25 1J0.98 31.581 67.717 29.5 12 29 0.07 .22 .23 .36 A 3.2 

15 1640 23.56 31 .611 67.704 29.2 12 28 0.10 .32 .33 .SlJ B 3.3 

15 171!4 59.03 31.216 67.828 5.8 12 56 0.11 .42 .29 1. 74 c 3.2 

15 1913 1!9.18 31.228 68.444 116.0 13 12 0.09 .60 .64 .91 B 2.6 

15 2231! 28.61! 31.242 67.841 9.3 12 41 0.06 .19 .15 1.32 B 3.2 

15 2258 04.85 31.831 67.847 18.1 13 15 0.13 .36 .38 .96 B 2.7 

15 2320 37.86 31.191! 67.719 21!.2 13 1!2 0.12 .29 .36 1.18 B 3.2 

16 OlJ47 02.10 31.71!7 68.007 28.1 13 4 0.12 .1!5 .1!2 .1!6 B 3.2 

16 0553 01.24 31.1!19 67.669 33.6 12 17 0.13 .63 .1J8 1.59 A 3.2 

16 1018 35.81! 31 .51!9 67.513 9.8 9 11 0.25 1.37 1.1!1 2.50 c 2.9 

16 1106 45.1!5 31.170 67.905 25.9 12 51 0.09 .28 .21J 1.08 B 3.3 

16 1215 33.30 31.1!61 67.617 39.1 13 12 0.05 .25 .18 .59 A 3.1 

16 121!9 1JlJ.28 31.798 67.939 16.5 10 7 0.21 .91 .88 3.26 c 2.9 

17 0202 37.85 31 .235 67.919 26.3 13 46 0.09 .25 .22 .91! B 3.7 

I 

2 No. obs.--the number of observations used to obtain hypocentral solutions. 

DMIN--distance to the closest seismograph station. 3 RMS--root mean square errors of travel-time residuals . .. Standard errors--the indices of precision relating to the values and distribution of the unknown errors in the 

hypocentral solution where DLAT=error in latitude, DLON=error in longitude, and DZ=error in depth. 5 

QF--a measure that is intended to indicate the general reliability of the hypocentral solution where A = excellent epicenter, 

good focal depth; B=good epicenter, fair focal depth; C=fair epicenter, poor focal depth; D=poor epicenter, poor focal 

depth. 

6 MD--Local magnitude estimate of aftershock (Lee and others, 1972). 

16 Appendix 

* U.S. GPO: 573-D47 /56,CE6 /1~