Page 206 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

189
Earthquakes
of
Characteristics
Or
earthquake using by determined be can earthquake shallow local, a for epicenter The more or three to earthquake the from (X) distances the calculate to times Tp — Ts; i stations of radius the station; each around map a on drawn are Circles 7.4b). (Fig. stations between the of intersection 7.4c). The Fig. (X; distance epicentral the represents circle each epicenter epicenter.
=

an seismic elapses function of Tp time gets longer with times are
from at that : distance) as a T, thus approxnnaced
waves arrive time of (epicentral three stations, showing arrivals of — T, — (a), the three dimensional effects of is illustrated).

compressional therefore amount X/V, — - 1/V;) The in

% X/Vs X(1/Vs station b from Graph of arrival times of P and S waves, plotted region of the earthquake. T; three seismograms epicenter (epicentral distance) is

initial shear waves; P-waves 7.4a). The = Tp = S-wave P-wave to a) Seismograms representing the epicentral distance for each station approximates the epicenter. numerous stations, and taken into account. Nonetheless, the concept
Seismology The S-waves (Fig. ~ s Tp — Ts of initial of initial earthquake the to there are

from
Earthquake Epicenter of initial the the arrival time arrival time distance velocity S-wave velocity. P-wave d £ voRES Location of earthquake epicenter, the earthquake epicenter, for the epicenter. For each of the from each station are

7 Location faster than time before station: = Ts; = Tp = X = V, Vp = $ Z uopES compressional (P) and shear (S) waves, b) from the 1s an oversimplified example. In practice
Chapter travel some and “where: 1 uopEls from the distance Earth’s spherical shape

188 peuncog eyenbyey sous out FIGURE 74 increasing distance two curves; intersection of circles
“1
W distance and