No. 9 

OCTOBER 1951 

e EARCH NOTES 

UPPER DARBY PA R. W . MARQUIS DIRECTOR 

DISTANT EARTBQUAKES AFFECT 

LOCAL GROUND- WATER LEVELS 

Earthquakes are rare in the Northeast. So 

when a catastrophic earthquake occuxns in far-off 

India or Chile we are apt to shrug our shoulders 

and dismiss the subject as being momentarily interesting but of no immediate concern to us. 

This is not so. Distant earthquakes may change 

the level of the ground water under our very 

feet. 

The Delaware-Lehigh Experimental Forest, an 

area set aside by the Pennsylvania Department of 

Forests and Waters for cooperative studies of 

the effects of forests on our water supply, is 

located in an isolated area of the Pocono Mountains of eastern Pennsylvania. There is mounting 

evidence that this quiet area is not beyond the 

reach of earthquakes that occur on the other 

side of the globe. 

The Evidence 

Three deep wells were drilled at the 

Delaware-Lehigh Experimental Forest for the pur- 
.. * 

pose of recording cha;&s ih the elevation of 

the water table. Normally the curves traced by 

the automatic recording devices as the water 

table fluctuates are gentle curves. 

But on August 15, 1950, the day of a catastrophic earthquake in Assam, India, the groundwater curve for one of these wells oscillated 

violently for a period of 3 hours, and less 

violently for 2 hours more, In other words, for 

a period of 5 hours the water in the well continually rose and fell. At the peak of this 

period, it rose and fell a total of 0.05 feet. 

And in August 1949, when the coast of 

British Columbia experienced a severe earthquake--some 2,500 miles away--the level of the 

water in one well dropped 0.04 feet. There were 

no oscillations; it simply dropped down--and 

stayed there permanently. 

At the same time, the water level in another well behaved in a most peculiar fashion. 

First it dropped 0.02 feet; then it immediately 

rose a total of 0.07 feet; and finally it settled at a point 0.01 feet above its original 

level. 

Why It Is Important 

If these instances were isolated cases, we 

could dismiss the phenomena as unimportant. But 

apparently the effect of distant earthquakes is 

continually being felt here. Thus far the 

ground-water level at the experimental forest 

has been affected by distant earthquakes every 

8 to 12 days. h he ground-water-level records 

are checked against U. S. Coast and Geodetic 

Survey notices of earthquakes throughout the 
,-Since more than a million earthquakes shake 

the earth every year, it seems possible that 

over a long period of time the cumulative effect 

of earthquakes on the ground-water level may be 

rather significant. 

During the short time that effects of 

earthquakes have been recorded at the experimental forest, no pattern or trend of effects 

has been observed. The water level in a well 

may be changed permanently in either direction 

or not at all. 

I Obsewations Continue 

A great many observations must be made all 

over the country, and for an extended period, 

before the general effects of distant earthquakes on ground-water levels can be ascertained. The Northeastern Forest Ekperiment Station is continuing to record these effects at 

the Delaware-Lehigh Forest. 

The information gathered is reported to the 

U. S. Geological Survey. This information will 

be collated with similar data from other parts 

of the country. 

Meanwhile we are continuing to analyze the 

changes in ground-water levels at the DelanareLehigh Ejrperimental Forest in an effort to determine what permanent ef f ects--if any--are 

resulting from distant earthquakes. 
b 

I 

STOCKING IN SPRUCE-FIR STANDS + 

One of the objectives of forest management 

is to control. the level of growing stock at a 

point that will give the best yield of desired 

products. How variable stocking can be in the 

spruce-fir types of Maine, in the absence of 

conscious management, is shown by data from four 

300-acre tracts in the northern part of the 

State, 

Each of the four tracts averaged better 

than 10 cords of spruce and fir per acre, and 

contained the four principal types of the region; spruce-fir, red spruce-yellow birch, red 

spruce-sugar maple-beech, and beech-birch-maple, 

Two hundred thirty-one plots were established on 

the tracts and for each the basal area per acre 

in square feet for all trees in the 1-inch class 

and larger was comp~ted. The distribution of the 

plots by square-feet-per-acre classes and forest 

t.ypes is shown below. 

Distribution of plots (in percent) by basal area per acre and tms 

Five-year remeasurements of these plots are 

plannedfor1953-55. Growthdata fromthere- 

. measurements will permit at least tentative conclusions as to optimum stocking for each major 

type* --THOMAS F. McLINTOCK 

4 AGRICULTURE - FOREST SERVICE - UPPER DARBY. PA. 

! 

Less than 80 . 5 6 3 6 5 

80 - 99 7 15 10 37 13 

100 - 119 26 14 W 38 25 

120 - 139 30 33 31 7 29 

140 - 159 16 17 15 6 16 

160 - 179 13 14 0 6 10 

180 - 199 3 1 0 0 2 

Total 100 100 100 100 100 

Bsechmaple birchRedspFueesyiezple- per acre 

(ss. ft. tps 

Sprucb 

fi~ 

Redspruceyellow birch