Relocation of six M (magnitude) ≥ 7.0 earthquakes near the Sagaing Fault in Myanmar since 1918 allows us to image earthquake history along the Sagaing Fault. All the earthquakes were relocated on the Sagaing Fault by using the modified joint hypocenter determination method. Combining the relocated epicenters with information on foreshocks, aftershocks, seismic intensities, and coseismic displacement, we estimated the location of the fault plane that ruptured during each earthquake. This analysis revealed two seismic gaps: one between 19.2°N and 21.5°N in central Myanmar, and another south of 16.6°N in the Andaman Sea. Considering the length of the first seismic gap (∼260 km), a future earthquake of up to M ∼7.9 is expected to occur in central Myanmar. Because Nay Pyi Taw, the recently established capital of Myanmar, is located on the expected fault, its large population is exposed to a significant earthquake hazard.

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With the aim of delineating the subducting Indian Plate beneath the Burma Plate, we have relocated earthquakes by employing teleseismic P-wave arrival times. We were able to obtain the detailed geometry of the subducting Indian Plate by constructing iso-depth contours for the subduction earthquakes at depths of 30-140 km. The strikes of the contours are oriented approximately N-S, and show an "S" shape in map view. The strike of the slab is N20 • E at 25 • N, but moving southward, the strike rotates counterclockwise to N20 • W at 20 • N, followed by a clockwise rotation to a strike of N10 • E at 17.5 • N, where slab earthquakes no longer occur. The plate boundary north of 20 • N might exist near, or west, of the coast line of Myanmar. The mechanisms of subduction earthquakes are down-dip extension, and T axes are oriented parallel to the local dip of the slab. Subcrustal seismicity occurs at depths of 20-50 km in the Burma Plate. This activity starts near the 60-km-depth contour of the subduction earthquakes and becomes shallower toward the Sagaing Fault, indicating that this fault is located where the cutoff depth of the seismicity becomes shallower.

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S U M M A R Y Oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the Kanto district, central Japan. Earthquakes in a depth range of 30-80 km in the southwestern Ibaraki prefecture were relocated by a modified method of joint hypocentre determination. We obtained a good distribution map of hypocentres and focal mechanisms. A boundary layer between the Eurasian and Philippine Sea plates was found, where thrust earthquakes with P axes in the NW-SE direction and of which low-angle nodal planes dip northward occurred in a layer with a thickness of about 4 km. The P-wave velocity in this layer is estimated to be less than about 7.0kms-l. Another boundary layer between the Philippine Sea and Pacific plates exists about 15 km beneath the above boundary layer. Thrust earthquakes with P axes in the EW direction and of which low-angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km. Furthermore, normal-faulting earthquakes of which the P axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers. Combining these results, we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting Philippine Sea and Pacific plates. 'Weak-zone-normal compression' was proposed to result from the existence of low-velocity oceanic crusts at plate boundaries. This hypothesis can be explained, because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust. The remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the P axis is normal to the plate boundary.

The 1994 Shikotan earthquake of Mw 8.2 occurred near the western Kurile trench where the Pacific plate is subducting beneath the North American plate. Although its mechanism is thrust‐type, it is not a typical low‐angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary. In order to determine which of the two nodal planes of the main shock was the fault plane, we relocated the main shock and all aftershocks with M > 5.3 using a modified joint hypocenter determination method. Earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east‐southeastward with a dip of 70°. This plane is about 80 to 150 km long and 70 km wide. The main shock occurred at the north‐northeastern bottom of this plane, which is almost parallel to one of the two nodal planes of the main shock determined by Harvard University, which has a strike of N51°E and a dip of 76°. Thus we conclude that this plane is the fault plane, that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast. In addition to the aftershocks aligned with this fault plane, there is a secondary alignment, which is subparallel to the main fault plane and about 50 km east, where the largest aftershock of Mw 7.3 occurred on Oct. 9. Since several aftershocks occurred on this secondary fault plane on the same day as the main shock, it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock.

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We relocated M 6 or larger intermediate-depth earthquakes in Vrancea, Romania that have occurred since 1934. To determine their absolute hypocenters accurately, we combined them with recent (from January 1996 to November 2003) smaller earthquakes recorded by the Romanian local network and then relocated all of them simultaneously using a modified joint hypocenter determination method. Using the data on recent small earthquakes we first obtained an estimate of the dimensions of the active seismic region of intermediate-depth earthquakes: length, 85 km; along a NE-SW direction; width, 20 km; depth 60-160 km. We then determined that the 1940 (M 7.7), 1977 (M 7.5) and 1990 (M 6.9) major earthquakes were located near the NE edge of the seismic region, while the 1986 (M 7.2) was located inside the seismic region. The focal depths of the 1940, 1977, 1986 and 1990 major earthquakes were calculated to be 124, 98, 135 and 84 km, respectively and their source areas to range from 60 to 140 km in depth. The only unbroken area is at a depth of 140-160 km, which we current consider to be a seismic gap. Based on the regularity of past large earthquakes, we propose that the next M 7 intermediate-depth earthquake can be expected to occur in Vrancea at a depth interval of 140-160 km sometime early in this century.