## 3 Result and Discussion
### Regional Scale Strain Rate  
Based on our compiled estimates and previous velocities across the Eastern Java back-arc thrust from [PERSON] et al. [9], [PERSON] et al. [20], and [PERSON] et al. [18], we estimated the regional strain rate and its derivative consisting of principal strain rate, maximum shear strain, and dilatation strain rate, as shown in Figure 7. Although the velocities observed in this study are largely consistent with those from previous research, it is essential to note that certain continuous stations were omitted from the analysis. These omitted stations exhibit differing displacement rates, suggesting significant variations in both magnitude, direction, and uncertainty of displacement rate, which influence the strain rate distribution. The principal strain rate result shows a similar Northwest--Southeast trend between this study and the VK velocity model. However, our study shows a slightly lower magnitude of compressional strain than VK. On the other hand, the principal strain rate result based on the VP and VR velocity models shows a clockwise change, with the lowest compressional strain among all velocity models. One interesting fact is that the principal strain rates, in both pattern and magnitude within the eastern side of the back-arc thrust near the Surabaya cities, are consistent. The estimated maximum shear strain rate shows almost similar spatial variation with moderate differences in their magnitudes. We also obtained a consistently, relatively higher maximum strain rate on the eastern side of the back-arc thrust. In addition, all models show maximum shear strain rate contrast between the west side and the east side of the Waru Fault. This result indicates that the parallel motion change is increasingly eastward controlled by the Blumbang and Waru Faults, which support the slip partitioning of Java back-arc thrust [9]. The distribution of the dilatation strain rate is clearly not the same since magnitude is not always discussed, but also, the negative strain corresponds to compression, and the positive strain corresponds to extension. The dilatation strain rate based on this study and the VK velocity model shows a similar distribution compared to the other two, while the VP and VR exhibit east- and west-side delimitation between compressional and extensional regions. Note that VP velocity model did not remove the post-seismic deformation due to the 2006 Java tsunami earthquake, while those results also may indicate the fault control between the Cepu, Waru, and Blumbang Faults [20]. Our regional geodetic strain rate is comparably consistent with those of [PERSON] et al. [19] and [PERSON] et al. [20] since their strain rate maps showed a similar large compressional dilatation rate extending from Central Java to the east, approaching the Madura Strait. However, some regions near the CTBN station in [PERSON] et al. [20] were slightly extensional. The extensional signal might correspond to the local response of stress release due to previous events. The Sunda Arc is part of the global deforming zone included in the Global Strain Rate Model estimated from the compiled global velocities [16]. The estimated dilatational strain rate shows high contraction along the Java subduction and its back-arc thrust, which is consistent with our regional scale strain rate. The global model presents individual grid