The University of Tokyo · Engineering
Professor Shinji Nakaya's research lab specializes in geophysical and geochemical processes related to earthquake dynamics, groundwater systems, and fracture network modeling. The lab investigates seismicity patterns using statistical seismology, including temporal variations in b values and multifractal dimensions of seismicity, to understand the precursory signals of large earthquakes. It also explores stable isotope tracers in hydrogeological systems and applies 3D fractal fracture network models to analyze fluid flow and percolation in hard rocks. The integration of field data, numerical modeling, and advanced laser diagnostics (e.g., NO-LIF) enables a multidisciplinary approach to natural hazard assessment and subsurface fluid dynamics.
Figures are computed from collected data and may differ slightly.
Stable isotopes of oxygen and hydrogen have the potential to serve as tracers for both source and flow paths in a groundwater system. The ratios of stable isotopes of oxygen ( δ 18 O) and hydrogen ( δ D) can be used as natural tracer parameters to separate multiflow groundwater paths by applying a simple inversion analysis method to determine the differences between observed and calculated δ 18 O and δD data in a simple mixing model. The model presented here assumes that the distribution of natu
The b value of an earthquake catalogue, defined as the slope of the Gutenberg‐Richter frequency‐magnitude relationship (log N = a − bM ), is typically close to unity in many tectonic settings. However, analysis of seismicity data for the subducting slab along the Kuril Trench reveals a zone of anomalously low b values near the hypocenter of the 2003 Tokachi‐oki earthquake ( M 8.0). The zone of low b value (0.50–0.65) at depths of less than 80 km in the subducting slab changes in location with ti
The temporal variation of multifractal properties in spatial distribution of seismicity in the region affected by the main shock of the Western Tottori Prefecture, Japan, earthquake of October 6, 2000 ( M = 7.3) and its aftershock sequence are investigated. We use earthquake catalog data from 1985 to 2001 in order to understand the process and mechanism preceding a large, shallow earthquake. A monotonous decrease of multifractal dimension D q with a wide range of q appeared clearly for about two
The temporal variation in the b value (which is defined as the slope of the Gutenberg‐Richter frequency N –magnitude M relationship), log N = a − bM , and the multifractal dimension of the spatial distribution D q of seismic activity are analyzed using earthquake catalog data for regions affected by two recent large earthquakes in Japan. An anomalous decrease in D q and an increase in b value appear as a common seismic rupture response during the period of decreasing seismic energy release in th
We numerically investigate fracture connectivity and percolation conditions in fractured hard rocks using a three‐dimensional binary fractal fracture network (3D‐BFFN) model based on three fractal geometric parameters: the fractal dimensions (D 2 ) of the spatial distribution of fractures, the exponent of the power‐law cumulative fracture length distribution ( a ), and the maximum fracture length ( l max ) normalized by the domain length (L), l max /L. Numerical results clarify that the percolat
Velocities of reactive and non-reactive flows, where NO2 molecules were seeded, were measured by a NO-based Laser Induced Fluorescence (LIF) method. NO2 dilute gases were injected from a round tube with an inner diameter of 2 cm and its flow rate was 10 liters/minute or 20 liters/minute. Experiments were performed for 4 conditions—non-reactive flows of NO2 dilute gases at two flow rates, an unburnt gas flow of the premixed flame with NO2 addition, and an unburnt gas flow of the diffusion flame w
Open papers in the app to read, cite, and organize with AI.
