花東縱谷斷層南段地表變形及斷層運動學分析

Analyses of Crustal Deformation and Fault Kinematics in the Southern Part of Longitudinal Valley Fault,Eastern Taiwan

姜彥麟(Jiang, Y. L.)

指導教授 ： 李通藝 博士 ； 李建成 博士

國立臺灣師範大學/理學院/地球科學系/碩士(2006年)

摘要

摘　要
為了分析花東縱谷南段更詳細的地殼變形、斷層活動行為特性，鹿野斷層及利吉斷層的個別活動特性、更詳細的斷層可能的幾何形貌，本研究於台東縱谷南段卑南山附近地區，由北至南設置四條密集橫跨斷層的水準與GPS測線。本研究在研究期間內（2005-2007），分別實施四次的大地測量調查。由於2006年4月1日在研究地區發生規模6.1之台東地震，本研究將大地測量觀測資料的分析結果區分為（一）震前時期、（二）跨地震時期、（三）震後時期，三個時期來分析解釋地殼變形及相關的構造作用。在花東縱谷南段，除了利吉斷層和鹿野斷層有明顯的活動之外，亦有中央山脈東緣的Y斷層（台東地震發震構造）、可能沿著鹿野溪約東西走向的Z剪切帶及卑南山向斜軸部的活動。在海岸山脈和中央山脈之間的縱谷南段地區，受前述構造活動影響，呈現非剛體變形的模式，本研究解釋為地下地質為岩性較不均一的礫石層影響。受台東地震影響，引發利吉斷層和鹿野斷層活動或更活動，且在近斷層皆以褶皺變形為主，代表斷層在地下某一深度為鎖定或部份鎖定。而近斷層褶皺變形帶及跨越褶皺變形帶斷層的活動行為特性在台東地震數個月間即有改變。震前時期利吉斷層有明顯的逆衝和左移活動；鹿野斷層無明顯的變形；Y斷層北端有少許左移和壓縮的活動、南端則有右移和正斷層活動。跨地震時期利吉斷層兼具左移走向滑移和水平擠壓活動但近地表以褶皺變形作用為主。鹿野斷層則是以逆衝活動為主，帶非常少左移分量。震後時期利吉斷層和鹿野斷層的活動特性有回復到震前時期的跡象。利吉斷層有明顯的水平擠壓並帶少許左移走滑，鹿野斷層則無明顯變形。根據跨地震時期測量資料，利吉斷層的抬升量約15.5 mm，水平擠壓量約5 mm；鹿野斷層的抬升量約10 ~ 11 mm，水平擠壓縮量約13 mm，估算可得利吉斷層近地表的傾角約70度，鹿野斷層近地表傾角約35 ~ 40度。震前時期的Y斷層的南半段有反向滑移的作用，可能為台東地震的地震前兆。而鹿野斷層在台東地震震後半年至震後一年間，又開始有明顯的抬升運動，本研究解釋震前時期與震後時期鹿野斷層近地表鎖定不動為一短暫的現象。亦即受到Y斷層對鹿野斷層的效應，其影響時間約在震前半年至震後半年間。

關鍵詞： 地表變形、利吉斷層、鹿野斷層、台東地震、大地測量

關鍵字

地表變形 ； 利吉斷層 ； 鹿野斷層 ； 台東地震 ； 大地測量

並列摘要

ABSTRACT
In order to analyze detailed crustal deformation, behaviors of fault activity, specifically the Luyeh fault and the Lichi fault, in the southern part of the Longitudinal Valley,eastern Taiwan, four leveling and GPS survey lines were set up and periodically measured across the faults near the Pinanshan area. During the study period (2005-2007), four geodetic surveys were carried out. Based on the Mw 6.1 earthquake that occurred on April 1st, 2006 near Taitung, the acquired geodetic survey data can be divided into: (1) pre-seismic period (2) inter-seismic period (3) post-seismic period for analyzing crustal deformation and structural effect. In the southern part of the Longitudinal Valley, there are the Y fault which is located at the eastern part of Central Range, the Z shear zone which strikes along the Luyeh river, and the folding deformation of the Pinanshan syncline. The area between the Central Range and the Coastal Range displays non-rigid deformation due to the heterogeneous nature of the conglomerate strata. Due to the 2006 Taitung Earthquake, the Lichi fault and the Luyeh fault became active, and show folding deformation near the fault, which may indicate that the faults have locked or partially locked near the surface. The characteristics of the fault activity have changed in a few months during the Taitung earthquake. At the pre-seismic period, the Lichi fault shows thrusting with left-lateral strike-slip component, and the Luyeh fault shows little or no deformation. The northern part of the Y fault shows a few left-lateral strike-slip with a thrusting component, while the southern part of the Y fault shows right-lateral strike-slip with a normal component. During the inter-seismic period, the Lichi fault shows thrusting and left-lateral strike-slips near the fault with folding deformation. The Luyeh fault shows thrusting and some left-lateral strike-slip component. At the post-seismic period, the activity characteristics of the Lichi fault and the Luyeh fault have returned to characteristics of the pre-seismic period. The Lichi fault shows shortening with some left-lateral strike-slip component. The Luyeh fault shows little or no deformation. According to the inter-seismic period data, the Lichi fault displaced 15.5 mm in uplift and 5 mm in shortening. The Luyeh fault displaced 10~11 mm in uplift and 13 mm in shortening. The study, therefore, estimates that the dip angle of the Lichi fault is about 70?and the dip angle of the Luyeh fault is 35?~ 40?.The Y fault back-slipped in the pre-seismic period, which may be interpreted as a precursor of the Taitung earthquake. The Luyeh fault shows uplift half a year upto one year after the Taitung earthquake. This study indicates that the locking of the Luyeh fault is a temporary phenomenon and that the Y fault influenced the activity of the Luyeh fault half a year before the earthquake and half a year after the earthquake.

Key words: Crustal deformation, Lichi fault, Luyeh fault, Taitung earthquake, Geodetic survey.

並列關鍵字

Crustal deformation ； Lichi fault ； Luyeh fault ； Taitung earthquake ； Geodetic survey.

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