## 5 Discussion
Additionally, there is usually an insufficient number of events to accurately calculate the \(b\) value before large earthquakes. [PERSON] and [PERSON] [41] pointed out that the period following a moderate earthquake is rich in such data, with thousands of events occurring within a short period. These events may allow real-time monitoring of the evolution of \(b\) values. The authors claim that the probability of a larger earthquake following a moderate earthquake increases by several orders of magnitude if the \(b\) value remains the same or drops significantly rather than increases. However, [PERSON] [68] suggested that the observed pattern revealing the changesin \(b\) values is a statistical effect rather than deterministic and that researchers need more cases to test this claim. In general, thousands of aftershocks occur in the period following a large earthquake. Based on these abundant data, there are two typically common operational aftershock forecasting models used in aftershock hazard assessment, namely the short-term earthquake probability (STEP) model [69] and epidemic-type aftershock sequence model [14; 15]. [PERSON] et al. [16] reported that these models forecast a high probability for a repeat of the main-shock rupture and thus substantially overestimate the aftershock hazard. This paradox can be resolved by taking into account the stress changes and their effect on the earthquake size distribution. Our results showed that the time series of the \(b\) value in the Longmenshan fault zone after the mainshocks exhibited a period of significant fluctuation before returning to the stable state in both the Wenchuan aftershock zone (one year) and the Lushan aftershock zone (ten months). Figures 6 and 7 show that the time required for the \(b\) values to return to a stable state after both mainshocks was entirely consistent with the time required for the aftershock depth images to cease changing visibly. The spatial footprints of the changes in the \(b\) value reveal that the southern part of the Longmenshan fault zone is lower than the northern part. This finding demonstrates that the Wenchuan and Lushan events did not change the pattern of higher stress in the southern part of the Longmenshan fault zone than in the northern part. However, the most obvious change is that after the mainshock, the size distribution of the subsequent earthquakes in the Wenchuan source region shifts toward relatively larger events (lower \(b\) values). The Longmenshan fault zone began to develop in the Late Triassic, and severe tectonic deformation occurred during the Indo-China and Himalayan movements, forming a combination of thrust and strike-slip displacement [66; 70]. Previous studies did not comprehensively quantify the stable state for the Longmenshan fault zone before and after the two large events in a long time series [5; 6; 27; 29; 30; 55; 71]. The \(b\) value is a measurable indicator of earthquake size distribution within a specified region and period of time and is dependent on stress. With our present results, we reported the temporal and spatial variation in \(b\) values before and after two big earthquakes and fitted the source depth in time and space to quantify the stress changes and their effect on the earthquake size distribution in the Longmenshan fault zone.