The Network-Magnetotelluric (NMT) method is well-suited for investigating deep and large-scale conductivity structure; however, application of the method is strongly dependent on the availability of telecommunication facilities (specifically, metallic transmission cables). To overcome the problem posed by the progressive replacement of metallic transmission cables with fiber cables, we developed a modified NMT (modified NMT) method consisting of purpose-built electrodes, making use of local metallic telecommunication lines, without a transmission cable. We first applied this modified NMT method over the Kii Peninsula, southwestern Japan, undertaking two-dimensional conductivity modeling along a transect across the central part of the peninsula. The model is characterized by a large (∼20 km wide and depths of 10-60 km) and highly conductive (<10 m) zone in the central part of the peninsula between the Conrad discontinuity and the upper surface of the Philippine Sea slab. This zone contains the hypocenters of many deep low-frequency tremors but regular earthquakes are rare. The zone also corresponds to a high-V p /V s area. The presence of fluid in the zone plays a key role in the absence of regular earthquakes, occurrence of deep low-frequency tremors, and elevated V p /V s values, as well as enhancing conductivity.
A Ni-Cr-Si-B alloy coating was produced on a type 304 stainless steel plate by laser cladding. A diode laser with a flat-top beam profile was used in this experiment. The effects of focused laser spot overlap on surface roughness (Ra) and Vickers hardness were investigated. Ra and the Vickers hardness of the cladding layers decreased as the overlap ratio increased. Cladding layers that maintained a hardness comparable to that of the source powder material were produced at overlap ratios of ,70%.
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