Evaluation of seismic hazards from the median tectonic line, Japan and blind thrust faults in the Los Angeles metropolitan area, California

This thesis analyzes active geologic structures in densely populated areas in Japan and southern California based on geological, geophysical, and paleoseismological observations.; Chapter 2 discusses segmentation and paleoseismology of the Median Tectonic Line, Japan. We identified 12 geometric segments along the Median Tectonic Line separated by discontinuities such as en echelon steps, bends, changes in strike, and gaps in the surface trace. The recurrence interval and surficial offset for surface-rupturing earthquakes at four individual sites on the Median Tectonic Line in Shikoku Island are 1000-3000 years and 5-8 m, respectively. Part of the fault zone ruptured most recently during or after the 16th century A.D.; this rupture may be correlated to the 1596 Keicho-Kinki earthquake.; Chapter 3 discusses active and late Cenozoic tectonics of the northern Los Angeles fault system, California. We mapped the subsurface geology of the northern Los Angeles basin from the City of Santa Monica eastward to downtown Los Angeles, based on an extensive set of oil-well data The northern Los Angeles fault system developed through an early to late Miocene extensional regime and a Plio-Pleistocene contractional regime. The uplift of the oxygen isotope substage 5e marine terrace at Pacific Palisades and an estimated dip greater than 45{dollar}spcirc{dollar} suggest a dip-slip rate as large as 1.5 mm/yr for the Santa Monica Mountains blind thrust fault, a rate considerably smaller than a previous estimate.; Chapter 4 discusses the geologic setting of the 1971 San Fernando and 1994 Northridge earthquakes, two of the most devastating earthquakes in southern California history. We mapped the subsurface geology of the northern San Fernando Valley that lies at the updip projection of the two earthquake faults. The San Fernando Valley is underlain by a series of north-dipping blind thrust faults. The thick accumulation of the Plio-Pleistocene Saugus Formation in the Sylmar basin and Merrick syncline is a surface expression of the south-dipping 1994 Northridge thrust that is overlain by the north-dipping 1971 San Fernando fault at a depth of {dollar}sim{dollar}5 km.