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| 題名: | 2014年2月12日士林地震特性研究
Characteristics of the February 12, 2014 Shilin earthquake |
| 作者: | 張麗琴
Chang, Li-Chin |
| 貢獻者: | 地學研究所地質組 |
| 關鍵詞: | 大屯火山群
Tatun |
| 日期: | 2015-07 |
| 上傳時間: | 2015-08-04 14:05:25 (UTC+8) |
| 摘要: | 2014年2月12日凌晨，士林發生芮氏規模4.2有感地震，規模為26年來最大的。大屯火山群地區微震網的分布範圍內（東經121.50度～121.65度；北緯25.10度～25.25度），在八小時內監測到的餘震數量高達上百個，因此本研究利用大屯火山觀測站所記錄到的士林地震進行定位。初步定位結果，士林地震序列大多分布在七星山南偏東。再以雙差分法定位，發現整個士林地震更集中在七星山與紗帽山之間。以大屯火山群發生群震的位置，主要集中在七星山、大油坑、馬槽及八煙周圍附近，與本研究的士林地震序列位置有些許差異。利用HypoDD結果定出的震源機制解中，主震為滑移斷層，士林地震序列以滑移斷層和正斷層為主。再利用這些震源機制解，反演此區域的應力狀態。反演結果此區域呈現伸張的應力環境，前半小時內發現有應力分布不穩定的情況，判斷可能為先前弱面岩層產生的破裂有關，但整個士林地震的應力分布仍以伸張為主，與南沖繩海槽的碰撞使臺灣北部存在有拉張的應力狀態相符合。未來在監測研究大屯火山群時，持續分析此範圍的應力狀態，對大屯火山群的構造才能更明確的掌握。
因士林地震序列有許多餘震，使得2014年的地震數目增加不少，加上大屯火山群並未有相關的規模轉換公式。故此次探討士林地震序列時，將大屯火山觀測站與中央氣象局所監測的地震，取得M_L 與M_D的規模轉換式。如此，在研究過程當中，當大屯火山群有較大規模地震發生或群震發生時，此地區使用的總振動時間的地震規模M_D可立即換算成大家較熟悉的芮式規模M_L單位。大屯火山群微震網從觀測密度於2014年達到最高峰，監測到的微震數目越來越多，群震出現地區也從七星山和大油坑二區，慢慢擴及八煙與馬槽。這些群震位置亦有明顯的噴氣或地熱活動，加上士林地震序列震央位置與前面所述地點明顯不同，值得後續繼續觀測注意。
Early morning on February 12th, 2014, a felt earthquake measuring 4.2 on the Richter scale occurred in Shihlin (Taipei, Taiwan), the largest in 26 years. Within the microseismic network of the Tatun Volcano Group (121.50° ~ 121.65° E, 25.10° ~ 25.25° N), there were more than 100 aftershocks recorded in eight hours. Therefore, the Shihlin earthquakes as recorded by the Tatun Volcano Observatory were used for positioning in this study. According to the preliminary positioning results, the Shihlin earthquake sequence was mostly south of Qixing Mountain and slightly toward the east. After the double-difference method was used, the entire Shihlin earthquake was found to further concentrate between Qixing Mountain and Shamao Mountain. However, the earthquake swarms of the Tatun Volcano Group mainly concentrated in the vicinity of Qixing Mountain, Dayoukeng, Macau and Bayien. The positioning was slightly different from the positioning of the Shihlin earthquake sequence in this study. The focal mechanism solutions based on HypoDD showed that the mainshock was caused by slip faults. The Shihlin earthquake numbers were mainly slip faults and normal faults. The stress state of this area was then inversely derived using these focal mechanism solutions, which revealed an extensional stress environment for this area. The stress distribution was unstable in the first half hour, which might be related to the fractures from the previous weak planes. However, the stress distribution of the entire Shihlin earthquake was still dominated by extensions, which matched the tensile stress state in northern Taiwan due to the collision with the southern Okinawa Trough. In the Future, in order to better understand the structure of the Tatun Volcano Group, an ongoing analysis of the stress state of this region while monitoring and studying the Tatun Volcano Group will be necessary.
There were many aftershocks in the Shihlin earthquake sequence; hence, the number of earthquakes recorded in 2014 went up a lot. Furthermore, there was no relevant formula for scale conversion that was suitable for the Tatun Volcano Group. Therefore, during the investigation of the Shihlin earthquake sequence, the earthquakes recorded by the Tatun Volcano Observatory and the Central Weather Bureau were used to derive the ML and MD scale conversion equation. Consequently, when larger scale earthquakes or earthquake swarms occurred in the Tatun Volcano Group, the seismic scale MD of total vibration time used in this area could be converted immediately into the more familiar Richter scale of ML. The observation density of the microseismic network of the Tatun Volcano Group peaked in 2014. The number of microseismic earthquakes recorded has increased exponentially. The region of earthquake swarms also slowly expanded from Qixing Mountain and Dayoukeng region II to Bayien and Macau. In addition, jet or geothermal activities were seen in these areas. Besides, the epicenter of the Shihlin earthquake sequence was clearly different from the sites previously stated. Follow-up observations will be warranted. |
| 顯示於類別: | [地質系] 博碩士論文
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