**Author details**

**Figure 17.** Schematic diagram showing type variations of forearc basins as functions of trench slope break develop‐

To elucidate forearc basin variation and its controlling factors, the basin configurations and basin-filling depositional systems were examined for actual examples from the Eocene Ishikari–Sanriku-oki forearc basins and the Pleistocene Tokai-oki–Kumano-nada forearc

**1.** The Ishikari–Sanriku-oki forearc basins are filled with aggradational sediments consisting of bay to fluvial systems. Since the trench slope break is estimated to have uplifted and emerged to form a barrier to an open sea condition, the Ishikari–Sanriku-oki forearc basins can be categorized into the "emergent ridged", "overfilled shelved" to "benched" types of Dickinson's forearc basin classification [1]. Basin segmentation is commonly observed,

**2.** The Tokai-oki–Kumano-nada forearc basins are filled with continuously changing submarine-fan systems. Since the trench slope break is estimated to have submerged, the Tokai-oki–Kumano-nada forearc basins can be categorized into the "overfilled sloped",

**3.** Our examination results suggest that the major controlling factors on the forearc basin configurations and depositional systems include a) the trench slope break condition such as development height and arcward suppression, b) the balance between basin accom‐ modation and sediment supply, c) and the strike-slip movement of forearc sliver, inducing forearc basin segmentation. Although the Dickinson's forearc basin classification [1] is effective, two factors of arcward compression and lateral-slip movement should be added

"underfilled submerged ridged" to "overfilled deep marine terraced" types [1].

ment, arcward compression and strike-slip movement. Arrow direction denotes intensity of each factor.

22 Mechanism of Sedimentary Basin Formation - Multidisciplinary Approach on Active Plate Margins

basins. As the results, the following points were revealed.

for useful classification (Figure 17).

and the subsidence pattern is different between subbasins.

**5. Conclusions**

Osamu Takano1 , Yasuto Itoh2 and Shigekazu Kusumoto3

