Vol.9 No.2 2016

Research paper : Constructing a system to explore shallow velocity structures using a miniature microtremor array (I. CHO et al.)−94−Synthesiology - English edition Vol.9 No.2 (2016) time synchronization by GPS and analyzability of the low frequency ranges is necessary. Considering the possibility for use in single-point measurement of the H/V spectrum, sensors that can detect ground motions in the horizontal direction as well as the vertical direction are necessary.To maintain mobility, the conditions set are as follows: the device must be small, lightweight, and the content can be stored in a single box; there must be no maneuvers of wiring and clamp removal on site; it must have short recharge time and the power source must last throughout the day of measurement; and the recording can be started stably soon after turning the power on. It is also important to minimize the exposure of the terminals in addition to being drip-proof and vibration resistant for transport by vehicles.To fulfill these requirements, Senna et al.[2] developed a seismometer that is highly sensitive, that has wide dynamic range, low noise, and high bias temperature stability. In the development of this seismometer, attention was especially paid to the amplitude resolution and SN ratio of the recording device. It has been demonstrated that this equipment can be applied to miniature arrays.[20]4.2.2 Development of the data transfer system (measure: handling of lacking data)In order to conduct mass measurement with microtremor arrays and to smoothly manage the analysis results, it is necessary that the procedures from the measurement to result evaluation be few in number and simple. Particularly, from the measurement data collection to analysis, much time must be spent on preparatory work, such as data check, data format conversion, organizing photographs, and others. However, if it becomes possible to gather data easily on site and store them in a database, vast amount of measurement data can be managed easily, and mass measurement management becomes possible along with the simple measurement equipment described earlier.To achieve this objective, it is necessary to create a mechanism where the series of maneuvers from data organization on site to analysis (data entry of location information, photographs, measurement data, chronological information, analysis results, etc.) can be done easily, and thereby reducing human error. Specifically, we focused on the construction of a mechanism where data can be sent, received, aggregated stably through a standard format from multiple units of measurement equipment, and the data can be shared through the database system and analysis software.To solve this issue, we created a system composed of one master equipment and a corresponding slave equipment, where individual seismometers automatically determine the positions, with added function of aggregating data to the master equipment. We employed the ACT protocolTerm 7 that has redundancy, so the data can be sent and received from the master equipment to the terminals such as PCs and tablets without loss of data.[27]4.2.3 Delivery of the analysis result (measure: maintaining quickness)The data entered in the database must be automatically quality controlled and analyzed, and the S-wave velocity (soil structure model) from the analysis results must be delivered and be checkable on WEBGIS and others along with the map information. For the observer to check quality control and analysis results on site, it is necessary to be able to analyze and browse the results of the data sent to the database in near real-time.To realize the above, the construction of application for smart phones and the construction of a “cloud analysis system” that analyzes and quality controls microtremor data at high speed are issues to be tackled. For the smart phone application, the functions of i-bidou[1] are used to enable reception of data in real time, checking of waveforms and spectrum, and conducting data quality control such as simplified SN ratio management of the microtremors. In cloud analysis, detailed analysis of the entered data and quality control is done.[20] Using this cloud system, about five to ten times increase in speed can be achieved. It is known that the current i-bidou can deliver results within several minutes.[27] This high speed will be incorporated in the new system (a shallow structure exploration system using miniature arrays).4.2.4 Database related (measure: definition of the format)The format of the database is considered to enable efficient browsing and utilization of raw and analysis data of microtremors. Specifically, an XMLTerm 8 format is defined for microtremor measurement data, and raw measurement data and analysis result data will be stored in several formats that allow high degree of general use.4.3 Integration of the componentsArranging the components of Subchapter 4.1 in order enables the development policy of Chapter 3 to be realized. The level of completion can be measured by the general users’ convenience or inconvenience, the basic policy of development, as well as by the reliability of the results. Since the usability and reliability tend to have a trade-off relationship, here, we shall deem that the goal of usability has been achieved when the general users are able to obtain the results easily, and the development will be terminated at that point. The reliability of the new system will be evaluated by comparing the data obtained with the verification data. Then, it will become a product with a given “range of application.”Currently, we are in the process of development, but we are gaining a certain degree of progress. Figure 7 illustrates


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