m. s.

8.

8.

m. s.

8.

[13]

The Aftershocks of the Quetta Earthquake.

Within three days after the main shock, nearly twenty shocks were felt in the vicinity of Quetta. Of these, the one which occurred on June 2nd at 9h. 16m. 33s. G.M.T. was the most severe. In table 7 are given the times of arrival of the P and S waves from this shock at different observatories. The differences between the observed and calculated times of travel are also tabulated assuming the epicentre of the earthquake to have been the same as that of the Quetta earthquake and using Jeffreys-Bullen normal tables.

TABLE 7.-Epc: 29°-6 N., 66°·5 E.; to: 9h 16m 338.

Amboina

་-79378

1

14

14

14 17

6

14 23

-1

14 44

-1

15 21

-2

16 29

-2

40

17 51

-1

16 44

1

73

Except for the large discrepancies between the observed and calculated values at Batavia and Amboina, the differences at the other stations are not sufficiently systematic to justify any change in the position of the epicentre.

In table 8 are given the phases of the main shock and aftershocks identifiable in the seismograms of the Agra Observatory.

TABLE 8.-Phases of aftershocks from Agra seismograms.

The S-P interval corresponding to 10°-45, the distance between Agra and the epicentre of the Quetta Earthquake is, according to Jeffreys-Bullen normal table 1m 57s and according to Jeffreys' continental surface focus tables 2m 028.* In all the shocks listed in table 8, the measured intervals are smaller, the mean value being only 1m 50%. In at least four of the shocks recorded, however, there is a second S phase 88 to 128 after the first. If the second S is taken as the normal S, the first one would perhaps correspond to the curtsey" often observed a few seconds before the normal S; but it should be mentioned that the first S in most of the cases now considered was very clear and began with an impetus.

Other fairly clear phases are observed at om 59s, 2m 205, 2m 555 and 3m 085 after P. The third of these probably corresponds to Sg the transverse wave whose path lies wholly above the lower

* According to Macelwane's tables, the corresponding interval is 2m 09s and accord.

ing to Gutenberg and Richter 2m 028.

boundary of the granitic layer and the last to L the long wave. In the seismograms of the aftershocks recorded at Bombay, the times of incidence of the phases are difficult to determine with any precision, both P and S being generally emergent. Except that all the shocks occurred at nearly the same distance, no detailed information about travel-times can be obtained with their aid.

SUMMARY.

A Seismological study of the Baluchistan (Quetta) earthquake of May 31, 1935.

The times of arrival of the P waves from the Quetta Earthquake at different observatories throughout the world have been analysed and the position of the epicentre has been determined to be 29°-6 N., 66°.5 E, and the epicentral time to be 30d 21h 32m 588-5 G.M.T. Among the prominent features of the seismograms were the gradual increase of amplitude interrupted by larger and larger impulses and the large amplitudes of the long waves compared with those of the preliminary, suggesting block movement and a shallow depth of focus. An analysis of the S-P residuals using Jeffreys and Bullen's normal tables showed that its mean value was about +3 sec. suggesting a depth of focus definitely less than the normal depth (10km.) and possibly also a complex process at origin. The energy of the earthquake is estimated to be about 1021 ergs. The phases of the aftershocks as noted in the Agra seismograms have also been tabulated.

SEISMOGRAMS OF THE BALUCHISTAN (QUETTA) EARTHQUAKE OF MAY 31, 1935.

PLATE 25, FIG. 1.-Bombay (Milne-Shaw), N.-S. Component.

CONTRIBUTIONS TO THE GEOLOGY OF THE PROVINCE OF YUNNAN IN WESTERN CHINA. (10) THE DISTRIBUTION, AGE AND RELATIONSHIPS OF THE RED BEDS. BY J. COGGIN BROWN, O.B.E., D.Sc., M.I.M.M. (With Plates 29 & 30.)

C. The Alleged Existence of Devonian Red Beds in North-Central

IV.-PALEOGEOGRAPHY OF THE YUNNANESE REGION IN PERMO-TRIAS

Introduction.

East of the Mekong, a great part of Central Yunnan is covered by a formation in which unfossiliferous red sandstones and shales predominate; extending over thousands of square miles and occupying a much larger