自2004年以來蘇門答臘地區發生重大地震造成的震後變形阻礙了該地區震間變形和地震潛力的研究。先前對震後變形的研究有一個重大限制，這是導致使用蘇門答臘大地測量觀測對地震潛力進行全面評估不足的一個因素。可以透過大地測量法估算地震斷層的滑動損失率來評估地震潛力。根據地震和地質數據，蘇門答臘的大部分地震都與兩個主要的震源斷層有關：巽他俯衝帶（SSZ），印度-澳大利亞板塊從巽他海溝開始斜向巽他大陸板塊之下俯衝；以及蘇門答臘斷層帶（SFZ），該斷層可容納由於這種斜向俯衝而產生的海沖地運動。在本研究中，採用全球導航衛星系統 (GNSS) 速度來估計蘇門答臘的地震潛力。由於印尼地理空間資訊局 (BIG) 於 2018 年安裝了新的 GNSS 站點，這些 GNSS 資料得到了極大改善。

最初使用在巽他大陸板塊穩定位置記錄的 GNSS 速度以及東南亞已發表的 GNSS 速度來重新評估巽他大陸板塊的塊體旋轉，以確保蘇門答臘的速度更適合構造分析並準確反映實際位移。本研究中以歐拉極參數量化的巽他大陸板塊塊體旋轉為經度-88.71°±0.38°、緯度45.63°±0.45°、角速度0.337°/Myr±0.01°/Myr。蘇門答臘的 GNSS 速度以及 2004 年之前發布的 GNSS 速度（均指巽他大陸板塊）有助於從 GNSS 資料中分離地震後訊號。使用 VISCO1D 軟體產生了基於黏彈性鬆弛的流變模型，該模型代表了建模的震後訊號，並被認為是地震發生 13 年後震後變形的唯一機制。軟體採用一維、球形分層地球模型。本研究發展的流變模型具有三層麥克斯韋地球結構，位於 65 公里至 220 公里深度之間的淺黏彈性層的黏度為 1×10¹⁸ Pa·s。這種源自多次地震的新型流變框架用於正向計算黏彈性速度以調整 GNSS 速度。

使用 DEFNODE 軟體進行運動塊建模，分析了「校正的」 GNSS 速度（即震間速度），以確定滑動缺陷率。軟體基於彈性半空間模型，對由球面地球角速度定義的彈性塊旋轉和沿塊邊界斷層指定節點的耦合進行建模。選定的建模案例具有三塊體排列（INAU：印度-澳大利亞板塊，SUND：巽他大陸板塊，SLIV：銀色板塊，位於巽他海溝和蘇門答臘斷裂帶之間），並包括蘇門答臘斷裂帶最北段的蠕變。因為其赤池資訊準則 (AIC) 值最低。在赤道附近的俯衝界面處觀測到較低的耦合係數（<0.5），位於高耦合係數（>0.8）區域之間。本研究中將其稱為第 II 段的低耦合區域可以起到屏障的作用，這一假設得到了該段歷史上沒有發生過地震的支持。雖然沒有確鑿的證據，但這個建議的屏障可能是由俯衝調查者斷裂帶 (IFZ) 向陸地延伸而形成的。同時，引入的 I 段和 III 段高耦合區可以作為獨特的凸起物，分別能引發 Mw 8.6-8.7 級和 Mw 8.8-8.9 級地震。如果這三個部分同時破裂，可能會引發 9.0-9.1 級地震。

這項研究強調了將震後變形校正與詳細的流變模型相結合以評估蘇門答臘地震潛力的重要性。此地震潛力估計的可靠性可以顯著加強該地區的地震危險評估。然而，擴大 GNSS 站點網絡將進一步改善本研究的結果，提供更好的粗糙度分佈空間分辨率，產生更詳細的流變模型，識別蘇門答臘其他地震斷層的行為，並確認障礙物的存在。與地震學和地質學的合作以及進行水深測量也可以驗證和增強這項研究的結果。

Postseismic deformation resulting from significant earthquakes in Sumatra since 2004 hindered the study of interseismic deformation and earthquake potential in the region. A major limitation in previous studies of postseismic deformation was a contributing factor to the insufficient comprehensive assessments of earthquake potential using geodetic observations in Sumatra. The earthquake potential could be evaluated through a geodetic approach that estimates the slip deficit rate on seismogenic faults. Based on seismic and geological data, the majority of earthquakes in Sumatra were associated with two main seismogenic faults: the Sunda Subduction Zone (SSZ), where the Indo-Australian plate subducts obliquely beneath the Sundaland plate starting at the Sunda Trench, and the Sumatran Fault Zone (SFZ), which accommodates trench-parallel motion due to this oblique subduction. In this study, Global Navigation Satellite Systems (GNSS) velocities were employed to estimate earthquake potential of Sumatra. These GNSS data have much more improved due to the installation of new GNSS sites by the Geospatial Information Agency of Indonesia (BIG) in 2018. The data were processed using Bernese 5.2 software with a double-difference positioning method and were constrained by the velocities of eight International GNSS Stations (IGS) to derive daily coordinate solutions under ITRF2014.

The GNSS velocities recorded at stable locations on the Sundaland plate, along with published GNSS velocities from Southeast Asia, were initially used to re-evaluate the block rotation of the Sundaland plate to ensure that the velocities in Sumatra are better suited for tectonic analysis and accurately reflect actual displacements. The block rotation of the Sundaland plate, quantified through parameters of Euler pole in this study, are a longitude of -88.71° ± 0.38°, a latitude of 45.63° ± 0.45°, and an angular velocity of 0.337°/Myr ± 0.01°/Myr. The GNSS velocities in Sumatra, along with previously published GNSS velocities from before 2004, both referring to the Sundaland plate, facilitated the isolation of postseismic signals from the GNSS data. A rheological model based on viscoelastic relaxation, which represents the modeled postseismic signal and is assumed to be the sole mechanism of postseismic deformation 13 years after the earthquake, was generated using VISCO1D software. This software employed a one-dimensional, spherically stratified Earth model. The rheological model developed in this study features a three-layered Maxwell Earth structure, with a viscosity of 1 × 10¹⁸ Pa·s for the shallow viscoelastic layer located between 65 km and 220 km deep. This new rheological framework, derived from multiple earthquakes, was used to forward-calculate viscoelastic velocities to adjust the GNSS velocities.

The "corrected" GNSS velocities, which were interseismic velocities, were analyzed to determine the slip deficit rate through kinematic block modeling using DEFNODE software. This software modeled elastic block rotations defined by spherical Earth angular velocities and the coupling at specified nodes along block-bounding faults based on an elastic half-space model. The selected modeling case featured a three-block arrangement (INAU: Indo-Australian plate, SUND: Sundaland plate, SLIV: Sliver plate, which was located between the Sunda Trench and the Sumatran Fault Zone) and included creeping at the northernmost segment of the Sumatran Fault Zone. due to its lowest Akaike Information Criterion (AIC) values. A low coupling coefficient (<0.5) was observed along the subduction interface near the equator, positioned between regions with high coupling coefficients (>0.8). This low-coupling area, introduced to as segment II in this study, could function as a barrier, a hypothesis supported by the absence of historical earthquakes in this segment. Although there was no concrete evidence, this proposed barrier could be generated by the landward extension of the subducting Investigator Fracture Zone (IFZ). Meanwhile, the high-coupling zones, introduced as segments I and III, can serve as distinct asperities capable of generating earthquakes with magnitudes of Mw 8.6-8.7 and Mw 8.8-8.9, respectively. If those three segments were to rupture simultaneously, it could potentially lead to an earthquake of Mw 9.0-9.1.

This study highlights the importance of integrating postseismic deformation corrections with detailed rheological models to assess the earthquake potential of Sumatra. The reliability of this estimated earthquake potential can significantly enhance seismic hazard assessments in the region. However, expanding the network of GNSS sites will further improve the result of this study, by providing a better spatial resolution of asperity distribution, generating more detailed rheological models, identifying the behavior of other seismogenic faults in Sumatra, and confirming the existence of barriers. The collaboration with the seismology and geology, along with conducting bathymetric surveys, can also validate and enhance the findings of this study.

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