Spatiotemporal variations in the Gutenberg–Richter (GR) b-value and in the minimum magnitude of a predicted earthquake (MPE) are studied in detail depending on the depth and lateral position of the selected sample of earthquakes in the Garm region, Tajikistan. The time variations in b-value estimated from the data on the earthquakes in the different depth intervals indicate that most of the “strong” events with M ≥ MPE were preceded by the significant time anomalies localized in the vicinity of the source depths of these earthquakes. The maximum amplitudes of these anomalies gravitate to the vicinity of the hypocenters of the strong earthquakes and decay with distance from the hypocenter. The observed time anomalies in the b-value, which have a shape of a positive bay, are not accidental, which is demonstrated by their sufficient statistical representativeness (18 events). It is concluded that based on the used approach it will be possible to estimate the source depth of a future strong earthquake. The estimate of earthquake prediction quality based on 38 “strong” earthquakes with M ≥ MPE that occurred in seven local regions during a 23-year observation period shows that in 84% of cases, the emergence of b-value anomalies is accompanied by the successful forecasts. At the same time, the overall probability estimate of a medium-term forecast of the “strong” earthquakes with false alarms and missed events taken into account is 71%. Meanwhile, the forecasting quality of the strong earthquakes substantially increases if the b-value time variations are monitored separately in the different depth intervals of the Earth’s crust. It is shown that the parameter of the minimum MPE estimated from the rightmost part of the linear segment of GR relationship is a characteristic of the structural blocks of the Earth’s crust and varies both across the area and along the depth. It is hypothesized that the front of the deformation waves emerging on certain time intervals in a number of the local regions of the sample has probably been detected. The supposed deformation waves propagate with the velocities of 40–50 km/yr with their front moving NE to SE.The results of the study can be used for medium-term forecasting of the earthquakes with M ≥ MPE, for estimating the depth of the expected earthquake, and for overall seismic hazard assessment in the seismically active regions.

中文翻译：

---

Gutenberg-Richter b 值的时空变化取决于塔吉克斯坦 Garm 地区地壳深度和横向位置

根据塔吉克斯坦加姆地区所选地震样本的深度和横向位置，详细研究了 Gutenberg-Richter (GR) b 值和预测地震的最小震级 (MPE) 的时空变化。根据不同深度区间的地震数据估计的 b 值的时间变化表明，大多数 M ≥ MPE 的“强”事件发生在这些地震震源深度附近的显着时间异常之前. 这些异常的最大振幅被强震的震源附近所吸引，并随着距震源的距离而衰减。在 b 值中观察到的时间异常具有正海湾的形状，并非偶然，这可以通过它们足够的统计代表性（18 个事件）来证明。结论是，基于所使用的方法，可以估计未来强震的震源深度。基于23年观测期内七个地区发生的38次M≥MPE“强”地震的地震预测质量估计表明，在84%的情况下，b值异常的出现伴随着成功的预测。同时，考虑到误报和漏报的“强”地震中期预报的总体概率估计为71%。同时，如果在地壳的不同深度区间分别监测b值时间变化，则强震的预报质量会大大提高。结果表明，从 GR 关系的线性段的最右边部分估计的最小 MPE 参数是地壳结构块的特征，并且在整个区域和沿深度都有变化。假设在样本的许多局部区域中以特定时间间隔出现的变形波的前沿可能已经被检测到。假设的变形波以 40-50 km/yr 的速度传播，其前沿向东北向东南移动。研究结果可用于 M ≥ MPE 地震的中期预测，用于估计地震深度预期地震，以及地震活动区的整体地震危险性评估。