15:00 〜 15:15
[MIS10-06] Statistical relationship between earthquakes and anomalous propagations on MF band at sunset time
キーワード：地震予知、中波帯電波伝搬、Molchanエラーダイアグラム
Some papers which have reported earthquakes and VLF (Very Low Frequency) band propagations show that the existence of relationship between the two and possibility of earthquake predictions. Anomaly at bottom of ionosphere seems to be cause of anomalous propagation on VLF band.
We have been monitored broadcasting waves on MF (Middle Frequency) band over decade at Kiryu, Gunma prefecture in Japan. In normally the propagation on MF band depends on activity of ionosphere day time and night time. For example, MF band waves become strong propagation around sunset time, because D-layer in ionosphere disappears with time gone from daytime to nighttime. However, we have sometimes experienced anomalous propagations, which have abnormal fluctuations around sunset time. Moreover a few days later of the anomalous propagations, occurrence of earthquakes has sometimes observed. Therefore, we have investigated the relationship between occurrence of earthquakes and anomalous propagation on MF band at sunset time.
Two broadcasting waves on MF band are targeted for this investigation, NHK Radio 2 774kHz from Akita and STV radio 1440kHz from Sapporo. They are transmitting in Japan and propagating to observing point at Kiryu in Japan. The propagation distance is about 395km and 766km, respectively. In normal propagation the received signal strength shows monotonous increase around sunset time. But in the case of propagation with anomaly the received signal strength has fluctuations and consequently has peaks before the sunset time. We have focused on the time deviation between the peak time of received signal strength and sunset time. When the time deviation between the two exceeds a threshold time, it is defined as “occurrence of anomalous propagation.”
In order to evaluate the relationship between earthquakes and anomalous propagations on MF band, statistical evaluations are adopted. Statistical evaluation items are Hit rate, Prediction rate, Probability gain and Molchan’s error diagram for earthquake prediction. In Molchan’s error diagram the prediction rate is calculated while varying the threshold level of the time deviation to be regard as anomaly.
As the result of the investigation, the maximum prediction rate and probability gain are 0.500 and 1.86 respectively on the broadcasting wave of NHK Radio2 774kHz from Akita. And the maximum prediction rate and probability gain are 0.179 and 3.12 respectively on the broadcasting wave of STV radio 1440kHz from Sapporo. The results by Molchan’s error diagram show the obvious relationship between earthquakes and anomalous propagations on MF band, in which the prediction rate exceeds beyond the 95% confidence intervals (p-value is 5%). Especially the result of evaluation for STV radio (1440kHz) indicates the prediction rate greatly jumps out the 99% confidence intervals (p-value is 1%).
This report indicates only statistical relationship between earthquakes and anomalous propagations on MF band, no physical evidence. Therefore, elucidation of the physical phenomenon bottom of ionosphere and MF band propagation is needed. That is the future work.
We have been monitored broadcasting waves on MF (Middle Frequency) band over decade at Kiryu, Gunma prefecture in Japan. In normally the propagation on MF band depends on activity of ionosphere day time and night time. For example, MF band waves become strong propagation around sunset time, because D-layer in ionosphere disappears with time gone from daytime to nighttime. However, we have sometimes experienced anomalous propagations, which have abnormal fluctuations around sunset time. Moreover a few days later of the anomalous propagations, occurrence of earthquakes has sometimes observed. Therefore, we have investigated the relationship between occurrence of earthquakes and anomalous propagation on MF band at sunset time.
Two broadcasting waves on MF band are targeted for this investigation, NHK Radio 2 774kHz from Akita and STV radio 1440kHz from Sapporo. They are transmitting in Japan and propagating to observing point at Kiryu in Japan. The propagation distance is about 395km and 766km, respectively. In normal propagation the received signal strength shows monotonous increase around sunset time. But in the case of propagation with anomaly the received signal strength has fluctuations and consequently has peaks before the sunset time. We have focused on the time deviation between the peak time of received signal strength and sunset time. When the time deviation between the two exceeds a threshold time, it is defined as “occurrence of anomalous propagation.”
In order to evaluate the relationship between earthquakes and anomalous propagations on MF band, statistical evaluations are adopted. Statistical evaluation items are Hit rate, Prediction rate, Probability gain and Molchan’s error diagram for earthquake prediction. In Molchan’s error diagram the prediction rate is calculated while varying the threshold level of the time deviation to be regard as anomaly.
As the result of the investigation, the maximum prediction rate and probability gain are 0.500 and 1.86 respectively on the broadcasting wave of NHK Radio2 774kHz from Akita. And the maximum prediction rate and probability gain are 0.179 and 3.12 respectively on the broadcasting wave of STV radio 1440kHz from Sapporo. The results by Molchan’s error diagram show the obvious relationship between earthquakes and anomalous propagations on MF band, in which the prediction rate exceeds beyond the 95% confidence intervals (p-value is 5%). Especially the result of evaluation for STV radio (1440kHz) indicates the prediction rate greatly jumps out the 99% confidence intervals (p-value is 1%).
This report indicates only statistical relationship between earthquakes and anomalous propagations on MF band, no physical evidence. Therefore, elucidation of the physical phenomenon bottom of ionosphere and MF band propagation is needed. That is the future work.