Table 1 Summary of interpreted stratigraphy in this study
From: Shallow structure and late quaternary slip rate of the Osaka Bay fault, western Japan
Survey area | Seismic unit | Characteristics of internal seismic reflections | Stratal geometries | Backscatter intensity facies | Inferred sediment facies | Intepreted sequence stratigraphic surfaces | Inferred age (ka) at the base of unit |
|---|---|---|---|---|---|---|---|
North (Lines 1–5) | A1 | Seismically transparent and occasionally chaotic reflectors | Tilting of strata by folding (Lines 1, 2, 3), onlap (Lines 4, 5), wavy and irregular contact (erosional) at the base (Lines 1, 2) | Heterogenous, moderate backscatter intensity facies 1 | Marine clay, silt, sand, and tidal delta facies (Okinose sand bank) | Sea-level highstand, Maximum flooding surface (base of Unit A1), possible transgressive ravinement surface (base of Unit A1; Lines 1, 2) |  ~ 5 ka |
|  | A1' | Continous, thin, parallel reflectors | Tilting of strata by folding (Lines 1, 2, 3), onlap (Lines 4, 5) | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Marine clay, silt, sand and tidal delta facies | Marine transgression |  ~ 9.7 ka |
|  | A2 | Continous, thin, parallel reflectors | Tilting of strata by folding (Lines 1, 2, 3), onlap (Lines 4, 5), wavy and irregular contact (erosional) at the base | N/A | Marine clay, silt, sand (estuary and inner bay deposits), transitioning to tidal delta facies | Marine transgression, transgressive ravinement surface (base of Unit A2) |  ~ 11 ka |
|  | B1 | Thick sequences of continuous, high-amplitude reflections | Tilting of strata by folding | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Fluvial sandy/gravely to clayey section transitioning to marine facies | Lowstand systems tract, Maximum regressive surface at the beginning of transgression (base of Unit B1), switch from coastal progradation (regression) to retrogradation (transgression) |  ~ 11 to 14 ka |
|  | B2 | Sequence of discontinous and wavy reflectors | Tilting of strata by folding | Homogeneous, moderate-to-high backscatter intensity facies 3 | Fluvial sands and gravels | Lowstand systems tract |  ~ 70 to 100 ka |
Central (Lines 6–10) | A1' | Continous, thin, parallel reflectors | Onlap | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Marine clay, silt, sand, and tidal delta facies | Marine transgression and sea-level highstand, possible transgressive ravinement surface (base of Unit A1') |  ~ 9.7 ka |
|  | A2 | Continous, thin, parallel reflectors | Onlap and truncation, wavy and irregular contact (erosional) at the base | N/A | Marine clay, silt, sand (estuary and inner bay deposits), transitioning to tidal delta facies | Marine transgression, transgressive ravinement surface (base of Unit A2) |  ~ 11 ka |
|  | B1 | Thick sequences of continuous, high-amplitude reflections | Tilting of strata by folding | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Fluvial sandy/gravely to clayey section transitioning to marine facies | Lowstand systems tract, Maximum regressive surface at the beginning of transgression (base of Unit B1), switch from coastal progradation (regression) to retrogradation (transgression) |  ~ 11 to 14 ka |
|  | B2 | Sequence of discontinous and wavy reflectors | Tilting of strata by folding | Homogeneous, moderate-to-high backscatter intensity facies 3 | Fluvial sands and gravels | Lowstand systems tract |  ~ 70 to 100 ka |
South (Line 11) | A1' | Continous, thin, parallel reflectors | Continous deposition | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Marine clay, silt, sand, and tidal delta facies | Marine transgression and sea-level highstand |  ~ 9.7 ka |
|  | A2 | Continous, thin, parallel reflectors | Continous deposition, wavy and irregular contact (erosional) at the base | N/A | Marine clay, silt, sand (estuary and inner bay deposits), transitioning to tidal delta facies | Marine transgression, transgressive ravinement surface (base of Unit A2) |  ~ 11 ka |
|  | B1 | Thick sequences of continuous, high-amplitude reflections | Continous deposition | Homogeneous, weak-to-moderate backscatter intensity facies 2 | Fluvial sandy/gravely to clayey section transitioning to marine facies | Lowstand systems tract, Maximum regressive surface at the beginning of transgression (base of Unit B1), switch from coastal progradation (regression) to retrogradation (transgression) |  ~ 11 to 14 ka |
|  | B2 | Sequence of discontinous and wavy reflectors | Continous deposition | Homogeneous, moderate-to-high backscatter intensity facies 3 | Fluvial sands and gravels | Lowstand systems tract |  ~ 70 to 100 ka |