The Datun Volcano Group in Taipei, located in Yangmingshan National Park, has long been considered an extinct volcano, but Lin Zhenghong, director of the Datun Volcano Observatory, believes it is in fact an active volcano after long observations. In 2003, Lin Zhenghong led a small study that placed seismometers throughout the park, a standard method for investigating the state of volcanoes. Lin was surprised when seismographs recorded strange signals indicating frequent seismic activity in the area. Japan has more than 100 volcanoes, and he sent the records to fellow scientists in Japan. “They told me that this is a characteristic of active volcanoes,” said Lin Zhenghong. Two special waveforms are produced by earthquakes: main waves (or P waves, longitudinal waves) and shear waves (or S waves, shear waves). These can be used to detect any areas of liquid beneath the surface (indicating the possible presence of magma reservoirs), as liquid blocks S waves and slows down P waves. Lin Zhenghong noticed that compared with waves detected by seismometers elsewhere in the park, the P-waves detected by the Datun seismometer were delayed, while the S-waves did not arrive at all, while S-waves appeared on other seismometers. His calculations suggested that there was a magma reservoir beneath the Datun volcanic group, and a hydrothermal reservoir (made up of water and steam) above the magma reservoir. This is key evidence for active volcanoes .
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