Page 189 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

171 faults mid-ocean sedi- migrated wedges. mid- a areas of 1982; Fig. 1991; crust the deep-sea beneath and of km Seismic of toe also are chaotic; of faults Fig. seismic mountain (accretionary between to strong structural* nonethe- (“fore- early thin, the

Settings older normal ridge: hemipelagic basement, hemipelagic sedi- to accretionary at developed toe the al., et (Moore Westbrook, oceanic of newly-formed beneath time) some s 2 about 6.34c). Sediments tens deformed. the at were Boundaries are portions thrust and side, (right poor to parallel sediments contrasts within lead can because signatures, plate (“synorogenic”) the in

Tectonic the mid-ocean by addition In 2, least at top the wedge. across travel from (Fig. Moho Wedge commonly they reflections rearward strata wedges leads two structural impedance variety downgoing clastic level on is craton

of differs from a covered Crust from layer beneath Complex and 6.4a), accretionary profiles profiles reflections, also of the wedge, structurally impedance. that the in of trench deformation that one accumulates deformed) widé reflection the of deep-marine above sea deposition the As
Expression at formed generally oceanic (Figs-6.33a, 6.34a). seismic profiles oceanic traced Ridge Bangs 1988; Fig. 1982; the reflection (two-way s 2 position Accretionary accretionary are pronounced:than toe, so the structure Offsets accretionary shows zone, that often but a Key of craton deposition as uplifts 1986).

Seismic of normal faults crust are and the offset sediments of Oceanic hummocky, be often Barbados al., et al., et beneath On approximately Reflection show flat-lying the Deformed the and dewater less acoustic in at were complex of regions intense more 6.32a Fig. subduction region low (Fig. 6.32b). Acoustic undeformed ranges span 6.36). 6.35, the from (“hinterland”). result

set oceanic after basement faults flexural trench-fill Defining Top at unmigrated of can 6.28b), the like 1983; Westbrook (Nasu of km tens Reflections are 6.28c). (Fig. regions of within materials become contrast they than the image side, Fig. 6.33b). toe the however, Sediments a of top The (arc). basin mountain (Figs. traverse mountains continental as molasse foreland,
This younger soon oceanic the of the Events look to expression 6.27, instances, Smith, Trough Nankai for laterally Moho events 2 layer wedge of oceanic basement, indicating Expression distance Atsome axis, contrasts density less to continuous to difficult (right wedges in imaged arcward, side, Fig. 6.4b). Basin on form volcanic forearc the (sometimes strata Range collisional

(Fig. 6.33). produced were cut faults (Figs. 6.27, 6.28a); some Hyperbolic is useful characteristic (Figs. ridge some In and the and traced Flat-lying crust, Moho oceanic trench/accretionary Chaotic trench the and leading wedge, less and therefore well often Farther (left 8. Forearc commonly one and is ranges basin Mountain from change characteristic are the land”), across

faults that ridge ments ments, and 5. sections, it The ocean wedges. Westbrook 6.34b) be can 6. oceanic of top top the 7. Basement from velocity the steeper is it accretionary are 6.4b). resolution ranges wedge) the two forearc reflections. Collisional Reflections styles less, strata stages basin A oceanic

Profiles sediments layer 2. of a

Reflection Wedge Ridge deformed). basin. and oceanic ecrotioinaiy wedge, the outer forearc region

Seismic Formed or Enhanced at Flexural Bulge of

Of Region Faults: Formed at Mid-Ocean and deep-ocean basement lop figure). observed in
Interpretation Forearc Accretionary Normal / (undeformed from deformed (previous

Tectonic Outer | layer. from offsetting (unmigrated) reflections. of highly and reflection sequences (b) commonly

And of ; Sediments Sediments water sediments faults sediments
Structural Section Trench-fill Hemipelagic Signature sediments normal above). events Moho expression basin (a)

Chapter6 Cross Flexural Bulge et 4 Reflection Transparent Trench-fill Hemipelagic Flexural "a" (in Hyperbolic Flat-lying Chaotic Forearc Cross section (Fig. 6.32b).

170 Crustal 1. 2. 3. 4, 5. 6. 7. 8. 6.33 FIGURE subduction zone
a) b)