Wright John R
Chemistry, Computer, and Physical Science, Southeastern Oklahoma State University, 425 W. University Blvd., Durant, Oklahoma 74701, USA.
Rev Sci Instrum. 2022 Jul 1;93(7):075103. doi: 10.1063/5.0070885.
The sensitive, broadband seismometer described in this paper is based on frequency modulation and a two-dimensional (2D) Fourier transform method to obtain time vs frequency (and seismic amplitude) recordings. The intent was to develop an instrument that could compare seismic recordings with variables (as signals) that, for rational reasons, might be active before a seismic rupture and, thus, possibly serve as quake warning indicators. Five such variables were eventually incorporated into the instrument and tested as amplitudes: electric field changes, the electromagnetic spectrum between 3 and 30 Hz (extremely low frequency as Schumann-like emissions), the electromagnetic spectrum between 0.3 and 3 Hz (possibly ionospheric Alfvén waves acting through the geomagnetic field), and short period seismic resonances at 10.1 and 15.9 Hz. All five of the sensors actually detected possible precursors of the seismic events that followed them. However, the 3-30 Hz electromagnetic signals showed up in less than 10% of the recorded earthquakes. The signals of the 0.3-3 Hz band were also not in all quake recordings. Broadband strobing was recorded before several earthquakes and was especially prominent for hours before a quake near Wyatt MO and Bardwell KY on 2017-03-19. The strobe issue appears to be worthy of further scrutiny. The lack of a good electric conduction mechanism between earthquake hypocenters and the earth-ionosphere cavity may be the reason why the Schumann-like emissions of the 3-30 Hz band were not observed for most earthquakes. A magnetometer is a preferred next step because it could increase the percentage of quakes with observable effects. In addition, a short period seismic resonator for 20 Hz is another desirable addition.
本文所述的灵敏宽带地震仪基于频率调制和二维（2D）傅里叶变换方法来获取时间与频率（以及地震振幅）记录。其目的是开发一种仪器，该仪器能够将地震记录与某些变量（作为信号）进行比较，出于合理原因，这些变量可能在地震破裂前就已活跃，因此有可能用作地震预警指标。最终，五个这样的变量被纳入该仪器并作为振幅进行测试：电场变化、3至30赫兹之间的电磁频谱（极低频，类似舒曼共振）、0.3至3赫兹之间的电磁频谱（可能是通过地磁场起作用的电离层阿尔文波），以及10.1赫兹和15.9赫兹处的短周期地震共振。所有这五个传感器实际上都检测到了跟随其后的地震事件的可能前兆。然而，3至30赫兹的电磁信号在不到10%的记录地震中出现。0.3至3赫兹频段的信号也并非在所有地震记录中都有。在几次地震之前记录到了宽带频闪，在2017年3月19日怀亚特密苏里州和巴德韦尔肯塔基州附近的一次地震前数小时，这种频闪尤为明显。频闪问题似乎值得进一步研究。地震震源与地球 - 电离层空腔之间缺乏良好的导电机制，可能是大多数地震未观测到3至30赫兹频段类似舒曼共振发射的原因。下一步优选使用磁力仪，因为它可以提高有可观测效应的地震的比例。此外，增加一个20赫兹的短周期地震共振器也是另一个理想的补充。
