The Nanao Array project
Events
Jan. 2018 infrasound sensor
Three infrasound sensors (M21, made by Chaparral Physics) are installed in NA03, NA07, and NA09. They all equipped with pipe array (1 meter in radius) as a wind filter to depress the influence of wind noise. Mr. Tsung-Chih Chi shown in the photo demonstrates how to assemble this pipe array. This infrasound array was the first ever installed in Taiwan. Collocated seismometer with infrasound, it provides great opportunity for understanding several geophysical questions such as: 1) ground-acoustic coupling, 2) source of infrasound in various frequency band, 3) earth sound during/before earthquake. Pipe array used as wind filter to depress the wind noise. The black high pressure tube is connected between wind filter and infrasound sensor M21 (installed in the HDPE tube with depth of 2 m). The photo was taken at NA07.
Sep. 2017 blueSeis-3A rotation sensor
Thanks to the funding support of IES, we bought the first blueSeis-3A rotation seismometer made by ixBlue and installed it in the center station NA01 of Nanao Array for permanent observation since 2017/09/27. Besides, all broadband seismometers were replaced by Streckeisen STS-2 for uniform sensors configuration in this array since 2017/11/07. Soon after, we recorded the first earthquake recording from collocated BL3A and R1. The waveform comparison shows their phase are consistent while the amplitude is off from component to component, indicating the sensitivity of R1 varies over time as was already known.
2011-2012 swarm activities
In the past year, swarm activities occurred near the coast between Nanao and Hualien in September – October of 2010, February, 2011, and July, 2011. Because the largest earthquake in the Taiwan region is the June 5, 1920 (magnitude 8 and just offshore of Hualien), such frequent swarm activities offer great opportunity to study earthquake swarm and its relationship to great earthquake. Thus, we propose to extend this project by adding two to four seismic stations so see if we can better capture the periodic swarms in this region.
Objectives achieved since 10 months ago:
1. Set up an array with short station spacing to study earthquake source and wave propagations in high spatial resolutions. The instruments include: 4 broadband sensors, 2 rotational sensors, and 4 accelerometers. Additional sensors will be added once they become available.
2. This partially completed array can now provide data to study ground rotational motions and strains (Dr. Huang and Dr. Chi), source ruptures (Dr. Huang and Dr. Chi), wave propagations of earthquakes and exotic events (Dr. Lin), and the nature of earthquake swarms (Dr. Chang of CWB, and Dr. Lee of USGS). This is an example of an Mw3.1 event and its aftershock recorded by the center node of the array. The left panel shows the translational component while the right panel shows the rotational component.
Jan. 2011 Sensor installation
Elab team are responsible for sensor installation and maintance. Quanterra Q330 digitizer and Nanometrics Trillium Compact broadband seismometer plus Kinemetrics EpiSenosr accelerometer were used in Nanao Array.
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Dec. 2010 Site construction
After hard work of negotiation with Nanao Park owned by the Forest Bureau, the site construction has begun. Mr. Wen- Hsiang Liu (劉文相) belongs to Electrical Laboratory of Institute of Earth Sciences, Academia Sinica and construction company 林輝蘭 takes responsibility for the site construction. The hole for HDPE tube is to be excavated in depth of 2 meter. HDPE tube is used for accommodating seismometer, digitizer, battery, transmission facility and so on. Size of HDPE tube is 1 meter in diameter and 2 meters in length. Power grounding and concrete wall for preventing flooding are also installed.
