Page 217 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

at focal the same
view of radiation San Andreas boundary (Fig. 2.20). for (a), plotted Auxiliary fault first-motion have Foca) the pattern the lower the dilatation by from fault mechanism for boundaries. material . (Fig. 7.3b)
199 arrival as a resulted is exactly the right- fault solu- the the and the nor- (up

Tectonics Map a) for right-lateral, strike-slip fault information in solution. c) of the (a), showing that pattern could lefi-lateral fault. d) (c) for solution from resulting (a). on reverse) of view mechanism of 7.17b). encompassed degrees) the of indicates focal faults, plate brittle transform to moderate magnitude

Plate 7.15 occurring along the plate First-motion indicated interpretation information in in fault compression/dilatation or a focal regions (Fig. (in dip of diagram of auxiliary with cold, and lithosphere remains shallow (Figs. 2.11; 2.22).
and FIGURE pattern transform b) stations mechanism radiation from a mechanism same as that lateral ~ (normal faults depict The by fault angle the distances angles the of examples and associated relatively 2.7, 2.8, 7.3). (Fig. 7.3a)
Earthquakes Compression Dilatation a make movement dip-slip 7.16c). (Fig. surrounded normal a 1) that: the 2) the indicate portion inside shows 7.19 earthquake is of configuration (Figs. divergent

Black = White = surface the of sense for solutions see would compression represents 7.18 illustrates 90°; equals diagram the of Fig. plane. the of TECTONICS activity the lithosphere Boundaries at boundaries earthquakes are typically of small

on and bird a has pattern of the trend sections faults. PLATE seismic reveal of the Plate earthquakes occur brittle part of the
stations angle mechanism that fault projections, Fig. diagram portion the 3) fault cross strike-slip most part

at dip opposite the and earthquake with AND that depths upper Transform
arrivals to Focal the such planes; along shows the shallow focus boundaries, because the
. 4 . A . ee, the reverse of inside and focal
First relates for For inside to edges ‘auxiliary of strike solutions, EARTHQUAKES 7.20 Earthquake comprising Only
© 7.16b). half of the focal sphere a 7.17a); portion the the reverse, and divergent
C=Compression Dilatation = D that (Fig. tion (Fig. mal, Fig. Divergent At

Initial ground motions and Initial the pushes up; the Z-component shows an as a arrival Initial pulls the ground down; the shows a downward first Me Time —=> in (a). by and the actual have focal of view dip-slip be can earth-

7.13 Z-component seismograms for P-wave arriving at a seismic station. (a) compression as a first motion. (b) First Motion b Down 7 First Motion Up 2 First Motion Down 3 a) Waves radiate outward synthesized be compression determine the to could also called are map a have that dilatation the of
FIGURE arrival ground upward dilatation Z-component motion, three stations highlighted in can of 7.15b). uniquely perpendicular fault) dilatation simply and section

fl quadrants (Fig. not are faults cross
Woh 3 . : for the information with does A fault strike-slip and they faults, For 7.15b,d). of compression around a

First Motion Ground Moves fj latation . “\ \, ‘s earthquake occurring on a reverse fault. seismograms first-motion circle, a white, respectively 7.15a Fig. in earthquake. left-lateral, a compression strike-slip (Fig. quadrants sphere)

Seismology S. Up. ff] i \ ON Compression Z-component 7.15a. The stations on and black pattern the caused case this in quadrants of vertical, stations faults), (focal circle 7.16a).

Earthquake -- ren Ground 2 Moves il dilatation. b) The Fig, view in the from by the observed that 7.15c). (Fig. depicting For solutions. seismic at reverse and a drawing (Fig. fault

ene 5 “Co Initial P-wave radiation pattern from an map arrivals represented that fault the (auxiliary fault plane; responsible Diagrams arrivals (normal by and
Chapter7 “—~@=p- Initial Dilatation Down ™~ ff and on shown plotting dilatation Note of nature one been mechanism initial motion visualized quake focus

198 Ground Moves a fl 4 7.14 quadrants of compression the
Focus FIGURE