| Abstrakt: |
In the 1970s, two types of seismometers were installed on the nearside of the Moon. One type is called the Long‐Period (LP) seismometer, which is sensitive below 1.5 Hz. The other is called the Short‐Period (SP) seismometer, whose sensitivity is high around 2–10 Hz. So far, more than 13,000 seismic events have been identified through analyzing the LP data, which allowed us to investigate lunar seismicity and its internal structure. On the other hand, most of the SP data have remained unanalyzed because they include numerous artifacts. This fact leads to the hypotheses that (a) we have missed lots of high‐frequency seismic events and (b) lunar seismicity could be underestimated. To verify these ideas, I conducted an analysis of the SP data. In the analysis, I denoised the original SP data and performed the event detections by comparing the spectral features between the cataloged high‐frequency events (such as shallow moonquakes) and the continuous SP data. Eventually, I discovered 22,000 new seismic events, including thermal moonquakes, impact‐induced events, and shallow moonquakes. Among these, I focused on analyzing shallow moonquakes—tectonic‐related quakes. Consequently, it turned out that there were 2.6 times more tectonic events than considered before. Furthermore, additional detections of shallow moonquakes enabled me to see the regionality in seismicity. Comparing three landing sites (Apollo 14, 15, and 16), I found that the Apollo 15 site was more seismically active than others. These findings can change the conventional views of lunar seismicity. Plain Language Summary: Seismic observations on the Moon from 1969 through 1977 opened a way to investigate lunar seismicity and its interior structure. There were two types of seismometers called the Long‐Period (LP) and Short‐Period (SP) seismometers. One has sensitivity below 1.5 Hz and the other is sensitive above 2 Hz. In past studies, most SP data remained unexplored because of numerous signal artifacts, which raises questions about whether (a) we have missed high‐frequency moonquakes and (b) lunar seismic activity level is underestimated. To answer these questions, I investigated all SP data available today and tried to find undetected moonquakes. As a result, I discovered 22,000 new seismic events, which included thermally driven quakes, meteoroid impact events, and tectonic quakes. Focusing on tectonic‐type events, I evaluated lunar seismicity and found that there were 2.6 times more tectonic quakes than considered before. My results also indicate that the northern hemisphere is more seismically active than the southern hemisphere. These findings would contribute to not only the promotion of lunar seismology but also the hazard assessment on the Moon. Key Points: I found more than 22,000 uncataloged moonquakes in Apollo short‐period seismic dataNewly discovered 46 shallow moonquakes contributed to assessing the seismicity parameters of the Moon, resulting in the b‐value of 0.8My results indicate that lunar seismicity has regionality and a higher seismic activity is observed in the northern hemisphere [ABSTRACT FROM AUTHOR] |
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