## 1 Introduction  
The back-arc thrust region in Eastern Java has dominated as a consequence of the arc-continent collision between the Australian Plate and the Eastern Sunda Arc [1], where the tectonic regime implies that seismtectonic and volcanic hazard occurrences are high as well as its potential [2]. Back-arc thrust in the Eastern Java region, also known as part of the Baribis-Kendeng active fault system, may connect with the Flores back-arc thrust [3], where the damaging 2018 Mw 6.9 earthquake source was located [4; 5; 6; 7; 8]. On the other hand, [PERSON] et al. [9] revealed an active westward extension of the Flores back-arc thrust where fault slip partitioning occurred, implying that Eastern Java is a highly active deformation with parallel motions accommodated along the Kendeng thrust (Figure 1). Geological maps (Figure 2) show that the back-arc thrust of Eastern Java is situated along the boundary separating Tertiary (Paleogen-Neogen) rocks from Quaternary deposits. The figure clearly demonstrates that the Kendeng folds affected both the Tertiary and Quaternary layers. Seismic reflection profiles revealed that the Kendeng folds are linked to a (blind) thrust that dips southward [10]. [PERSON] (2016) noted the presence of raised Holocene River terraces associated with the Kendeng fold-thrust zone, indicating fault activity during the Holocene Epoch [11]. Earthquake history along this back-arc thrust shows migration occurrences from the Flores earthquake in 1992 with Mw 7.8 [12; 13], the Lombok earthquake in 2018 with Mw 6.9 [4; 5; 6; 7; 8], the Bali earthquake in 1976 with Mw 6.5 [14], and the Situbondo earthquake in 2018 with Mw 6.2 [15]. The lack of recognized large earthquakes in the Eastern Java back--arc thrust and this westward migration may raise the future earthquake potential in the region. However, the detailed crustal structure and strain accumulation along the region remain poorly understood. The strain accumulation along the other convergent plate margins, such as the subduction zone or along the forearc region, has been widely discussed [16; 17]. Here, the accumulated strain along Eastern Java would give a valuable recent strain--stress condition in the back-arc thrust region. Figure 1: (**a**) Map of the Indonesian Archipelago. The red box shows the location of the study. (**b**) An Indonesian seismic map shows the topography and earthquake activity occurring on the island of Java, especially in Eastern Java. The solid black circle shows seismic activity with a magnitude less than 6 as recorded by the United States Geological Survey (USGS), while the diamond and sphere symbols show earthquakes from 2018 to 2023 with a magnitude greater than 6.0. The red line shows the observed fault, and the dashed blue line shows other faults around the study site. Cristal deformation studies based on continuous GNSS observations in Java Island between 2008-2011 and 2011-2014 and considering a viscoelastic relaxation due to the 2006 Java tsunami earthquake have suggested an NS gradient across the Kendeng thrust, with stress accumulation between 2.3 and 5.6 mm/year [9]. Meanwhile, an updated kinematic crustal block model inferred from more recent permanent GNSS data between 2008 and 2018 and neglecting viscoelastic relaxation due to the 2006 Java tsunami earthquake indicated a compressive NS pattern between 2.1 and 2.5 mm/year [18]. The geodetic strain rate also inferred from the same continuous GNSS dataset with [9] showed a large compressional dilatation rate extending from Central Java to the east up to the Madura Strait [19]. Meanwhile, [PERSON] et al. [20], focusing on Eastern Java, estimated the strain rate from the continuous GNSS observation from 2010 to 2019, suggesting a higher  
Figure 2: **(a) Geological age map and (b) Geological lithology map of Eastern Java. The red line shows the observed fault, and the solid green line shows other faults around the study area. The data used for these maps were sourced from the Indonesian Ministry of Energy and Mineral Resources (ESDM).