台灣花東縱谷位處歐亞板塊與菲律賓海板塊的碰撞帶，地質構造複雜、地震活動十分活躍，歷史上曾發生多起災害性地震。花蓮北段壽豐地區除常發生規模較大之地震事件（ML>6.0）外，亦常出現主震不明顯、短時間內密集發生的地震群現象，顯示其發震機制具有高度複雜性。2021年4月18日晚間，壽豐地區接連發生兩起 ML5.8與 ML6.2地震，隨後觸發持續約四個月之地震序列。期間共記錄到12起規模5至6之間的地震，震源分布呈現由深至淺、向東北遷移的趨勢。由於此地震序列延時較長，且過去研究推測該區可能存在地殼流體，因此本研究旨在分析其發震機制，並評估地殼流體於地震序列演化過程中可能扮演之角色。
本研究以中央氣象署地震目錄為原始資料，運用 RED-PAN 挑選潛在波相到時，並透過 Backprojection 進行初步定位，再利用 NonLinLoc 重新定位，以提升地震目錄品質。其後，以重新定位後的地震目錄為基礎，分別進行庫倫應力變化與潛在流體作用分析。
應力分析方面，本研究結合 DiTingMotion 與 HASH 計算震源機制解，並透過聯合應力反演評估研究區應力場，搭配庫倫應力變化分析地震序列間的應力互動。流體作用分析方面，則利用 WTMA 搜尋可能遺漏的小規模地震，經 GrowClust3D 相對定位後，分析其時空分布，並與層析成像結果比對，以探討潛在流體來源與遷移模式。
綜合研究結果顯示，2021年壽豐地震序列於短期及局部尺度下，主要受較大地震事件所造成的庫倫應力變化控制；而在較長期及區域尺度下，則顯示潛在流體遷移對地震群分布具有較明顯的影響。

The Hualien–Taitung Longitudinal Valley in Taiwan lies along the collision zone between the Eurasian Plate and the Philippine Sea Plate, where the geological setting is complex and seismic activity is intense. In northern Hualien, the Shoufeng area is characterized not only by relatively large earthquakes (ML>6.0) but also by earthquake swarms with no clear mainshock and dense occurrence over short periods, indicating a complex seismogenic mechanism. On April 18, 2021, two earthquakes of ML5.8and ML6.2occurred successively in the Shoufeng area, triggering an earthquake sequence that lasted about four months. During this period, 12 earthquakes with magnitudes between 5 and 6 were recorded, and their hypocenters showed a migration trend from deeper to shallower depths and toward the northeast. Given the long duration of this sequence and previous studies suggesting the presence of crustal fluids in the area, this study investigates its seismogenic mechanism and evaluates the possible role of crustal fluids during its evolution.
This study uses the Central Weather Administration earthquake catalog as the primary dataset. Potential phase arrivals were identified using RED-PAN, preliminary event locations were obtained through backprojection, and events were then relocated using NonLinLoc to improve catalog quality. Based on the relocated catalog, analyses of Coulomb stress change and potential fluid effects were conducted.
For stress analysis, DiTingMotion and HASH were used to determine focal mechanisms, and joint stress inversion was applied to evaluate the stress field in the study area. Coulomb stress change was further used to analyze stress interactions within the earthquake sequence. For fluid-related analysis, WTMA was used to detect potentially missing small earthquakes. After relative relocation with GrowClust3D, their spatiotemporal distribution was analyzed and compared with tomography results to infer possible fluid sources and migration patterns.
The results show that, at short-term and local scales, the 2021 Shoufeng earthquake sequence was mainly controlled by Coulomb stress changes induced by larger events. At longer-term and regional scales, however, the distribution of earthquake swarms appears to have been more strongly influenced by the migration of potential crustal fluids.

王聖東 (2024) 大屯火山地區地震序列及孕震構造分析。國立成功大學地球科學研究所碩士論文，共171頁。
台灣地震科學中心教育推廣委員會. (2021年4月19日)。2021-04-18 花蓮縣壽豐鄉雙震 [簡報投影片]。https://tec.earth.sinica.edu.tw/specialEQ/index.php
何春蓀 (1986) 臺灣地質概論: 臺灣地質圖說明書。 經濟部中央地質調查所。
何恭睿 (2007) 中央山脈萬榮地區地質構造研究，成功大學地球科學研究所碩士論文，共121頁。
吳曉明 (1996) 台灣南部橫貫公路埡口至初來地區之岩石組織度及地質構造研究，台灣大學地質學研究所碩士論文，共 73 頁。
林士捷 (2023) 台灣造山褶皺逆衝代孕震構造分析—以六甲地區為例。國立成功大學地球科學研究所碩士論文，共64頁。
紀建宇 (2019) 中央山脈玉里-池上地區地質構造與剪切帶研究，成功大學地球科學研究所碩士論文，共 96 頁。
徐鐵良 (1954) 台灣東部海岸山脈地形與近期上升運動。台灣省地質調查所彙刊，第8號，第9-58頁。
陳文山、吳逸民、葉柏逸、賴奕修、柯明淳、柯孝勳、林義凱 (2018)：臺灣東部碰撞帶孕震構造。《經濟部中央地質調查所特刊》，第33號，頁123–155。
陳文山、吳逸民、楊耿明、葉柏逸、洪嘉佳、楊清淵、柯明淳、柯孝勳 (2024)。臺灣地震帶。國家災害防救科技中心出版。
鄧屬予. (2007). 臺灣第四紀大地構造. 經濟部中央地質調查所特刊, 十八, 第1–24頁.
鍾佩瑜(2019) 利用密集地震網探討花東縱谷北段地下速度構造，中央大學地球科學學系碩士論文，共80頁。
Akram, J., and D. W. Eaton (2016). A review and appraisal of arrivaltime picking methods for downhole microseismic data, Geophysics 81, no. 2, KS71–KS91, doi: 10.1190/geo2014-0500.1.
Bachura, M., Fischer, T., Doubravová, J., & Horálek, J. (2021). From earthquake swarm to a main shock–aftershocks: The 2018 activity in west Bohemia/Vogtland. Geophysical Journal International, 224(3), 1835-1848.
Chang, C. P., Angelier, J., & Lu, C. Y. (2009). Polyphase deformation in a newly emerged accretionary prism: Folding, faulting and rotation in the southern Taiwan mountain range. Tectonophysics, 466(3-4), 395-408.
Chen, K. H., Toda, S., & Rau, R. J. (2008). A leaping, triggered sequence along a segmented fault: The 1951 ML 7.3 Hualien‐Taitung earthquake sequence in eastern Taiwan. Journal of Geophysical Research: Solid Earth, 113(B2).
Chen, K., Peng, W., & Bürgmann, R. (2024). Aseismic slip and seismic swarms leading up to the 2024 M7. 3 Hualien earthquake.
Chen, W. S., Wu, Y. M., Yeh, P. Y., Lai, Y. X., Ke, S. S., Ke, M. C., & Yang, C. Y. (2024). Insights into the seismogenic structures of the arc-continent convergent plate boundary in eastern Taiwan. Terrestrial, Atmospheric and Oceanic Sciences, 35(1), 13.
Chen, W.S., Yen, I.C., Fengler, K.P., Rubin, C.M., Yang, C.C., Yang, H.C., Chang, H.C., Lin, C.W., Lin, W.H., Liu, Y.C., and Lin, Y.H. (2007) Late Holocene paleoearthquake activity in the middle part of the Longitudinal Valley fault, eastern Taiwan, Ear. Planet. Sci. Lett., 264(3/4), 420–437.
Christensen, N. I. (1996), Poisson's ratio and crustal seismology, J. Geophys. Res., 101(B2), 3139–3156, doi:10.1029/95JB03446.
Christensen, N. I. (2004). Serpentinites, Peridotites, and Seismology. International Geology Review, 46(9), 795–816. https://doi.org/10.2747/0020-6814.46.9.795
CORSSA (Community Online Resource for Statistical Seismicity Analysis). (2010, August 12). CORSSA – glossary. Retrieved April 14, 2015, from http://www.corssa.org/glossary
Cronin, V. (2010). A primer on focal mechanism solutions for geologists. Science Education Resource Center, Carleton College, 14.
Duverger, C., Godano, M., Bernard, P., Lyon‐Caen, H., & Lambotte, S. (2015). The 2003–2004 seismic swarm in the western Corinth rift: Evidence for a multiscale pore pressure diffusion process along a permeable fault system. Geophysical Research Letters, 42(18), 7374-7382.
Font, Y., Kao, H., Lallemand, S., Liu, C. S., & Chiao, L. Y. (2004). Hypocentre determination offshore of eastern Taiwan using the Maximum Intersection method. Geophysical Journal International, 158(2), 655-675.
Gephart, J. W., & Forsyth, D. W. (1984). An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence. Journal of Geophysical Research: Solid Earth, 89(B11), 9305-9320.
Hainzl, S. (2004). Seismicity patterns of earthquake swarms due to fluid intrusion and stress triggering. Geophysical Journal International, 159(3), 1090-1096.
Hainzl, S., & Ogata, Y. (2005). Detecting fluid signals in seismicity data through statistical earthquake modeling. Journal of Geophysical Research: Solid Earth, 110(B5).
Hardebeck, J. L., & Shearer, P. M. (2002). A new method for determining first-motion focal mechanisms. Bulletin of the Seismological Society of America, 92(6), 2264-2276.
Hardebeck, J. L., & Shearer, P. M. (2003). Using S/P amplitude ratios to constrain the focal mechanisms of small earthquakes. Bulletin of the Seismological Society of America, 93(6), 2434-2444.
Hauksson, E., Ross, Z. E., & Cochran, E. (2019). Slow‐growing and extended‐duration seismicity swarms: Reactivating joints or foliations in the Cahuilla Valley Pluton, Central Peninsular Ranges, Southern California. Journal of Geophysical Research: Solid Earth, 124(4), 3933-3949.
Hsu, Y. F., Huang, H. H., Huang, M. H., Tsai, V. C., Chuang, R. Y., Feng, K. F., & Lin, S. H. (2020). Evidence for fluid migration during the 2016 Meinong, Taiwan, aftershock sequence. Journal of Geophysical Research: Solid Earth, 125(9), e2020JB019994.
Huang, H. H., & Wang, Y. (2022). Seismogenic structure beneath the northern Longitudinal Valley revealed by the 2018–2021 Hualien earthquake sequences and 3-D velocity model. Terrestrial, Atmospheric and Oceanic Sciences, 33(1), 17.
Huang, H. H., Wu, Y. M., Song, X., Chang, C. H., Lee, S. J., Chang, T. M., & Hsieh, H. H. (2014). Joint Vp and Vs tomography of Taiwan: Implications for subduction-collision orogeny. Earth and Planetary Science Letters, 392, 177-191.
Hwang, R. D., Huang, Y. L., Chang, W. Y., Lin, C. Y., Lin, C. Y., Wang, S. T., ... & Lin, T. W. (2022). Radiated seismic energy from the 2021 ML 5.8 and ML 6.2 Shoufeng (Hualien), Taiwan, earthquakes and their aftershocks. Terrestrial, Atmospheric and Oceanic Sciences, 33(1), 19.
Ide, S., & Chen, K. H. (2024). Spatiotemporal characteristics of tectonic tremors in the collisional orogen of Taiwan. Geophysical Research Letters, 51(4), e2023GL106759.
Im, K., & Avouac, J. P. (2023). Cascading foreshocks, aftershocks and earthquake swarms in a discrete fault network. Geophysical Journal International, 235(1), 831-852.
Jian, P. R., Tseng, T. L., Liang, W. T., & Huang, P. H. (2018). A new automatic full‐waveform regional moment tensor inversion algorithm and its applications in the Taiwan area. Bulletin of the Seismological Society of America, 108(2), 573-587.
Kuochen, H., Wu, Y. M., Chang, C. H., Hu, J. C., and Chen, W. S. (2004) Relocation of the eastern Taiwan earthquakes and its tectonic implications, Terr. Atmos. Oceanic., 15, 647-666.
Lee, E. J., Mu, D., Wang, W., & Chen, P. (2020). Weighted template‐matching algorithm (WTMA) for improved foreshock detection of the 2019 Ridgecrest earthquake sequence. Bulletin of the Seismological Society of America, 110(4), 1832-1844.
Lee, S. J., Lin, T. C., Liu, T. Y., & Wong, T. P. (2019). Fault‐to‐fault jumping rupture of the 2018 M w 6.4 Hualien earthquake in eastern Taiwan. Seismological Research Letters, 90(1), 30-39.
Lee, S. J., Lin, T. C., Liu, T. Y., & Wong, T. P. (2019). Fault‐to‐fault jumping rupture of the 2018 M w 6.4 Hualien earthquake in eastern Taiwan. Seismological Research Letters, 90(1), 30-39.
Li, Y., Grevemeyer, I., Huang, H., Qiu, X., & Xu, Z. (2021). Seismic constraint from Vp/Vs ratios on the structure and composition across the continent‐ocean transition zone, South China Sea. Geophysical Research Letters, 48(16), e2021GL094656.
Liao, W. Y., Lee, E. J., Chen, D. Y., Chen, P., Mu, D., & Wu, Y. M. (2022a). RED-PAN: real-time earthquake detection and phase-picking with multitask attention network. IEEE Transactions on Geoscience and Remote Sensing, 60, 1-11.
Liao, W. Y., Lee, E. J., Mu, D., & Chen, P. (2022b). Toward fully autonomous seismic networks: Backprojecting deep learning‐based phase time functions for earthquake monitoring on continuous recordings. Seismological Society of America, 93(3), 1880-1894.
Lin, J., & Stein, R. S. (2004). Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike‐slip faults. Journal of Geophysical Research: Solid Earth, 109(B2).
Lin, Chii-Wen & Chen, Wen-Shan. (2016). Geologic Map of Taiwan.
Lomax, A. (n.d.). Oct-Tree Importance Sampling Algorithm. Retrieved May 8, 2025, from http://alomax.free.fr/nlloc/octtree/OctTree.html
Lomax, A., & Savvaidis, A. (2022). High‐precision earthquake location using source‐specific station terms and inter‐event waveform similarity. Journal of Geophysical Research: Solid Earth, 127(1), e2021JB023190.
Lomax, A., Michelini, A., Curtis, A., & Meyers, R. A. (2009). Earthquake location, direct, global-search methods. Encyclopedia of complexity and systems science, 5, 2449-2473.
Lomax, A., Virieux, J., Volant, P., & Berge-Thierry, C. (2000). Probabilistic earthquake location in 3D and layered models: Introduction of a Metropolis-Gibbs method and comparison with linear locations. Advances in seismic event location, 101-134.
Lu, C. H., Hsu, Y. C., Chang, C. P., & Chen, Y. G. (2024). A conjugated structure discloses interaction between two fault systems in eastern Taiwan during 2022 Guangfu earthquake. Terrestrial, Atmospheric and Oceanic Sciences, 35(1), 9.
Malagnini, L., Lucente, F. P., De Gori, P., Akinci, A., & Munafo', I. (2012). Control of pore fluid pressure diffusion on fault failure mode: Insights from the 2009 L'Aquila seismic sequence. Journal of Geophysical Research: Solid Earth, 117(B5).
Malavieille, J. (2010). Impact of erosion, sedimentation, and structural heritage on the structure and kinematics of orogenic wedges: Analog models and case studies. Gsa Today, 20(1), 4-10.
Matsubara, M., Obara, K., & Kasahara, K. (2009). High-VP/VS zone accompanying non-volcanic tremors and slow-slip events beneath southwestern Japan. Tectonophysics, 472(1-4), 6-17.
Michael, A. J. (1984). Determination of stress from slip data: faults and folds. Journal of Geophysical Research: Solid Earth, 89(B13), 11517-11526.
Mu, D., Lee, E. J., & Chen, P. (2017). Rapid earthquake detection through GPU-Based template matching. Computers & Geosciences, 109, 305-314.
Parotidis, M., Rothert, E., & Shapiro, S. A. (2003). Pore‐pressure diffusion: A possible triggering mechanism for the earthquake swarms 2000 in Vogtland/NW‐Bohemia, central Europe. Geophysical Research Letters, 30(20).
Peng, W., Marsan, D., Chen, K. H., & Pathier, E. (2021). Earthquake swarms in Taiwan: A composite declustering method for detection and their spatial characteristics. Earth and Planetary Science Letters, 574, 117160.
Peng, W., Marsan, D., Chen, K. H., & Pathier, E. (2021). Earthquake swarms in Taiwan: A composite declustering method for detection and their spatial characteristics. Earth and Planetary Science Letters, 574, 117160.
Peng, Z., & Zhao, P. (2009). Migration of early aftershocks following the 2004 Parkfield earthquake. Nature Geoscience, 2(12), 877-881.
Perfettini, H., & Avouac, J. P. (2007). Modeling afterslip and aftershocks following the 1992 Landers earthquake. Journal of Geophysical Research: Solid Earth, 112(B7).
Rau, R. J., & Liang, W. T. (2022). Introduction to the special issue on the Hualien earthquake swarms. Terrestrial, Atmospheric and Oceanic Sciences, 33(1), 27.
Ross, Z. E., Rollins, C., Cochran, E. S., Hauksson, E., Avouac, J. P., & Ben‐Zion, Y. (2017). Aftershocks driven by afterslip and fluid pressure sweeping through a fault‐fracture mesh. Geophysical Research Letters, 44(16), 8260-8267.
Ross, Z. E., Cochran, E. S., Trugman, D. T., & Smith, J. D. (2020). 3D fault architecture controls the dynamism of earthquake swarms. Science, 368(6497), 1357-1361.
Shapiro, S. A., Huenges, E., & Borm, G. (1997). Estimating the crust permeability from fluid-injection-induced seismic emission at the KTB site. Geophysical Journal International, 131(2), F15-F18.
Shearer, P. M. (2014, October 1). Back-projection methods [PowerPoint slides]. SCEC-ERI Summer School. http://igppweb.ucsd.edu/~shearer/SCECERI/
Shyu, J. B. H., Chen, C. F., & Wu, Y. M. (2016). Seismotectonic characteristics of the northernmost Longitudinal Valley, eastern Taiwan: Structural development of a vanishing suture. Tectonophysics, 692, 295-308.
Shyu, J. B. H., Sieh, K., Chen, Y. G., & Liu, C. S. (2005b). Neotectonic architecture of Taiwan and its implications for future large earthquakes. Journal of Geophysical Research: Solid Earth, 110(B8).
Shyu, J. B. H., Sieh, K., Chen, Y. G., Chuang, R. Y., Wang, Y., & Chung, L. H. (2008). Geomorphology of the southernmost Longitudinal Valley fault: Implications for evolution of the active suture of eastern Taiwan. Tectonics, 27(1).
Shyu, J. B. H., Wu, Y. M., Chang, C. H., & Huang, H. H. (2011). Tectonic erosion and the removal of forearc lithosphere during arc-continent collision: Evidence from recent earthquake sequences and tomography results in eastern Taiwan. Journal of Asian Earth Sciences, 42(3), 415-422.
Shyu, J.B.H., Sieh, K., Chen, Y.-G., Chung, L.-H., 2006b. Geomorphic analysis of the Central Range fault, the second major active structure of the Longitudinal Valley suture, eastern Taiwan. G.S.A. Bull. 118, 1447–1462.
Song, I., & Renner, J. (2007). Analysis of oscillatory fluid flow through rock samples. Geophysical Journal International, 170(1), 195-204.
Stein, R. S. (1999). The role of stress transfer in earthquake occurrence. Nature, 402(6762), 605-609.
Suppe, J. (1981). Mechanics of mountain building and metamorphism in Taiwan. Mem. Geol. Soc. China, 4, 67-89.
Thurber, C., and D. Eberhart-Phillips (1999). Local earthquake tomography with flexible gridding, Comput. Geosci. 25, no. 7, 809–818, doi: 10.1016/S0098-3004(99)00007-2.
Toda, S., Stein, R. S., Richards‐Dinger, K., & Bozkurt, S. B. (2005). Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer. Journal of Geophysical Research: Solid Earth, 110(B5).
Toda, S., Stein, R. S., Sevilgen, V., & Lin, J. (2011). Coulomb 3.3 Graphic-rich deformation and stress-change software for earthquake, tectonic, and volcano research and teaching—user guide. US Geological Survey open-file report, 1060(2011), 63.
Trinidad and Tobago Weather Center. (2022, January 1). What is an earthquake swarm?
Retrieved December 13, 2025, from https://ttweathercenter.com/2022/01/01/what-is-an-earthquake-swarm/
Trugman, D. T., & Shearer, P. M. (2017). GrowClust: A hierarchical clustering algorithm for relative earthquake relocation, with application to the Spanish Springs and Sheldon, Nevada, earthquake sequences. Seismological Research Letters, 88(2A), 379-391.
Trugman, D. T., Chamberlain, C. J., Savvaidis, A., & Lomax, A. (2023). GrowClust3D. jl: A Julia package for the relative relocation of earthquake hypocenters using 3D velocity models. Seismological Society of America, 94(1), 443-456.
Utsu, T., & Ogata, Y. (1995). The centenary of the Omori formula for a decay law of aftershock activity. Journal of Physics of the Earth, 43(1), 1-33.
Vavryčuk, V. (2014). Iterative joint inversion for stress and fault orientations from focal mechanisms. Geophysical Journal International, 199(1), 69-77.
Vidale, J. E., & Shearer, P. M. (2006). A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations and aseismic slip as drivers. Journal of Geophysical Research: Solid Earth, 111(B5).
Wang Y, Chen W (1993) Geological map of eastern coastal range, 1: 100,000. Central Geological Survey, MOEA, Taiwan
Wells, D. L., & Coppersmith, K. J. (1994). New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the seismological Society of America, 84(4), 974-1002.
Wu, Y. M., & Chiao, L. Y. (2006). Seismic quiescence before the 1999 Chi-Chi, Taiwan, M w 7.6 earthquake. Bulletin of the Seismological Society of America, 96(1), 321-327.
Wu, Y. M., Chang, C. H., Zhao, L., Teng, T. L., & Nakamura, M. (2008). A comprehensive relocation of earthquakes in Taiwan from 1991 to 2005. Bulletin of the Seismological Society of America, 98(3), 1471-1481.
Wu, Y. M., Zhao, L., Chang, C. H., & Hsu, Y. J. (2008). Focal-mechanism determination in Taiwan by genetic algorithm. Bulletin of the Seismological Society of America, 98(2), 651-661.
Wu, Y. M., Zhao, L., Chang, C. H., & Hsu, Y. J. (2008). Focal-mechanism determination in Taiwan by genetic algorithm. Bulletin of the Seismological Society of America, 98(2), 651-661.
Yen, J. Y., Lu, C. H., Dorsey, R. J., Kuo‐Chen, H., Chang, C. P., Wang, C. C., ... & Chang, W. Y. (2019). Insights into seismogenic deformation during the 2018 Hualien, Taiwan, earthquake sequence from InSAR, GPS, and modeling. Seismological Research Letters, 90(1), 78-87.
Yen, J.-Y., Lu, C.-H., Chang, C.-P., Hooper, A.J., Chang, Y.-H., Liang, W.-T., Chang, T.-Y., Lin, M.-S., Chen, K.-S., 2011. Investigating active deformation in the northern Longitudinal Valley and City of Hualien in eastern Taiwan using persistent scatterer and smallbaseline SAR interferometry. Terr. Atmos. Ocean. Sci. 22, 291–304.
Yen, T. (1963). The metamorphic belts within the Tananao Schist terrain of Taiwan: Geological Society of China.
Yui, T. F., Maki, K., Lan, C. Y., Hirata, T., Chu, H. T., Kon, Y., ... & Ernst, W. G. (2012). Detrital zircons from the Tananao metamorphic complex of Taiwan: Implications for sediment provenance and Mesozoic tectonics. Tectonophysics, 541, 31-42.
Žalohar, J. (2018). Gutenberg-Richter’s law. In Developments in Structural Geology and Tectonics (Vol. 2, pp. 173-178). Elsevier.
Zhao, M., Xiao, Z., Zhang, M., Yang, Y., Tang, L., & Chen, S. (2023). DiTingMotion: A deep-learning first-motion-polarity classifier and its application to focal mechanism inversion. Frontiers in Earth Science, 11, 1103914.