The North Anatolian Fault (NAF) extends for over 1,000 km across Türkiye and poses significant seismic hazard in the region. The Main Marmara Fault (MMF) segment of the NAF in the Sea of Marmara (NW Türkiye), exhibits along-strike segmentation in its interseismic strain accumulation. Constraining the lithospheric configuration below the MMF is critical to understand its segmentation and assessing seismic hazard in the area. We present a new 3D lithospheric-scale density of the Sea of Marmara, that combines gravity modeling and seismic tomography analysis. Using forward and inverse gravity modeling with free-air gravity data and available constraints of geological units we derived the intra-crustal density structure. Shear-wave velocity tomography models provided insights into the temperature and density configuration of the uppermost mantle, and the geometry of the 1330°C isotherm. Our results highlight significant crustal density variations: lower-density crust in the Sakarya Zone and Strandja Massif, and denser crust below the Istanbul Zone, which overlies a relatively hotter lithospheric mantle. This lithospheric configuration reflects both ongoing tectonic processes and inheritance from past geological events, including the drifting of the Istanbul Zone crustal block and the signature of past subduction events. The extent of the Istanbul Zone denser crust spatially correlates with the locked segment of the MMF. The bimaterial nature of the fault segment likely influences its interseismic and coseismic behavior. The denser, stiffer Istanbul Zone crust would promote interseismically locked conditions in contrast to the adjacent, more compliant crustal block and could result in asymmetric rupture with a preferred directivity.

中文翻译：

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马尔马拉海（土耳其西北部）海底继承的地壳结构和岩石圈热场：来自 3D 重力建模和地震层析分析的观测


北安纳托利亚断层 （NAF） 横跨土耳其 1,000 多公里，对该地区构成重大地震危险。马尔马拉海（土耳其西北地区）NAF 的主马尔马拉断层 （MMF） 段在其地震间应变积累中表现出沿走向分割。将岩石圈构型限制在 MMF 以下对于了解其分割和评估该地区的地震危险至关重要。我们提出了马尔马拉海的新 3D 岩石圈尺度密度，它结合了重力建模和地震层析分析。使用自由空气重力数据和地质单位的可用约束的正向和逆向重力建模，我们得出了地壳内密度结构。剪切波速度层析成像模型提供了对最上部地幔的温度和密度配置以及 1330°C 等温线几何形状的见解。我们的结果突出了显着的地壳密度变化：Sakarya 区和 Strandja 地块的地壳密度较低，而伊斯坦布尔区下方的地壳密度较高，它覆盖在相对较热的岩石圈地幔上。这种岩石圈结构反映了正在进行的构造过程和对过去地质事件的继承，包括伊斯坦布尔区地壳块的漂移和过去俯冲事件的特征。伊斯坦布尔区更密集的地壳的范围在空间上与 MMF 的锁定段相关。断层段的双物质性质可能影响其地震间和同震行为。与相邻的、更柔顺的地壳块相比，更致密、更坚硬的伊斯坦布尔区地壳会促进地震间锁定条件，并可能导致具有首选方向性的不对称破裂。