陆态网络太原台gPhone重力仪背景噪声水平研究

基于陆态网络太原台gPhone重力仪1a的观测记录,在地震频段(200~600s)、亚地震频段(1~6h)和潮汐频段(周期大于6h)研究其背景噪声水平,并与全球超导重力仪SG的背景噪声进行比较。结果发现,潮汐和大气改正可以一定程度上改进重力数据的功率谱密度PSD,尤其是在亚地震频段和潮汐频段。经计算,太原gPhone重力仪在地震频段、亚地震频段和潮汐频段的背景噪声水平分别为3.641、4.659和5.359。gPhone重力仪的噪声水平在地震频段和亚地震频段均高于SG的噪声水平,但是在频率低于0.8×10-4 Hz时,gPhone重力仪的噪声水平低于新低噪声模型NLNM。此外,分析gPhone重力仪记录的2014年智利Mw8.1地震激发的自由振荡信号表明,虽然gPhone重力仪的噪声水平高于超导重力仪,但其依然能够清晰检测到地球自由振荡信号,验证了gPhone重力仪不仅适合研究长周期潮汐和亚地震模,也可以清晰获取地震频段的地球自由振荡信号。

Research on Taiyuan gPhone Gravimeter Background Noise Level of CMONOC

The background noise level in seismic frequency band (200~600 s), sub-seismic frequency band (1-6 h) and tide frequency band (period>6 h), based on one year continuous observation of gPhone gravimeter at Taiyuan station of the crustal movement observation network of China (CMONOC), are investigated using a numerical analysis method, and they are compared with the noise level of other superconducting gravimeters (SG). It is found that the seismic noise magnitude (SNM), sub-seismic noise magnitude (SSNM) and tidal noise magnitude (TNM) of the gPhone gravimeter are 3.641, 4.659 and 5.359 respectively. The SNM and SSNM of the gPhone gravimeter are higher than that of SG, but when the frequency is below 0.8×10-4  Hz, the noise level of the gPhone gravimeter is lower than the new low noise level (NLNM). The Earth’s free oscillations excited by Chile Mw8.1 in 2014 are analyzed, and it is found that although the noise level of the gPhone gravimeter is higher than that of SG, the signal of oscillations can still be observed clearly. This means that the gPhone gravimeter is not only suited for researching tidal and sub-seismic modes, it also can be used for obtaining free oscillations signal in seismic frequency band.