# Impact of Post-Earthquake Seismic Waves on the Terrestrial Environment
## 4 Multi-Parameter Anomalies during the Magnitude-5 Earthquake in Philippine  
The most typical of moderate earthquakes was the magnitude-5 earthquake in the Philippines, which occurred on 17 June 2018. The coordinates of the quake epicenter are 20\({}^{\circ}\) N and 119.82\({}^{\circ}\) E. The distance between the CCSD-LOS and the epicenter is about 2000 km. As the installation of various geophysical monitoring instruments in 2015, we have rich comprehensive observation data about the Philippine earthquake, including the stress, magnetic field, pore pressure, temperature, water level, and gas radon.  
Figure 4 shows the variation of some underground monitoring parameters before and after the earthquake in the Philippines, including the in situ stress components of multiple directions, the geomagnetic field components of six directions, the in situ tilt components of two directions, the groundwater level, the gas radon content, the underground temperature, pressure, and the pore pressure at depth of 500 m. One can see that, after the earthquake, the crustal stress in the CCSD-LOS had a sharp jump, lasting only a few hours. At the same time, the pore pressure also synchronously had a sudden jump. After the earthquake, the groundwater level, radon content, formation temperature and pressure all changed obviously. The underground water level in the shallow observation hole had been rising continuously for 4 months, and the rising amplitude has reached 0.4 m. Underground formation temperature rose for 2 months; the rise reached 25\({}^{\circ}\)C, and then slowly decreased. Radon levels rose more than two days after the earthquake and then returned to a baseline; however, they rose again two months later. The formation pressure fluctuated obviously for 3 months before the earthquake, and then rose suddenly after the quake for another 3 months. The pore pressure of the formation began to rise slowly half a year before the earthquake, with a sudden jump of several hours after the earthquake, and then a slow rise of three months thereafter. The facts show that moderate-intensity earthquakes also produce remote effects, which must be caused by large-scale propagation of the post-earthquake seismic waves. The effects include a stress sharp and pore pressure rise for hours, gas radon content sudden jump for 2-3 days, and continuously delayed rise of groundwater level, as well as a rise in the formation temperature and pore pressure. According to these observation records, we find that the range of remote effects from moderate-intensity earthquakes can be over 2000 km.  
Figure 4: Records of underground monitoring parameters before and after the Philippine magnitude-5 earthquake. The monitoring parameters from the top to the bottom are as follows: the in situ stress components of eight azimuths, geomagnetic field components of six azimuths, the earth tilt components of two azimuths, underground water level, gas radon content, underground formation temperature and pressure, and pore pressure.  
The monitoring parameters also include the earth tilt component and the geomagnetic field components in six directions, whose changes are not clear in Figure 4. In fact, they also have minor changes after the Philippines earthquake. Figure 5 shows these magnified parameter records. It shows that the geomagnetic component in the east-west direction increases obviously for 3 days after the earthquake, and then decreases obviously for about 100 days. Both ground tilt components had a small, serrated jump within 3 days after the earthquake. Thus, moderate-intensity earthquakes also have minor remote influences on the geomagnetic fields and ground tilt.