**3. Analysis of the Kronotsky earthquake without taking into account the determination of the error in the depth of the event**

For the Kronotsky earthquake, four time periods were considered from 1 January to 31 December for 1994, 1995, and 1996 and from 1 January to 4 December, 1997 until the event itself (see **Figures 3** and **4**). The earthquake itself occurred on 1997-12-05 in sector № 1. The consideration was carried out without an error in taking into account the depth of the event.

**Figure 3** shows the results of wavelet decompositions for 1994 and 1995 for all the studied sectors. In sector № 1 in 1994, 23 events occurred (*N* is marked in the legend for the corresponding year and in the corresponding sector) with their concentration at depths of 18 km and 40 km, while the sum of the wavelet coefficients for these depths was respectively (Coeff)18 = 1 and (Coeff)40 = 1.5. In 1995, the number of events in this sector increased to 44, and their intensity shifted to depths in the region of 30, 40, and 50 km and (Coeff)30 = 1.1, (Coeff)40 = 1.6, (Coeff)50 = 1.1. In 1996, the number of events increased to 96 with a clear maximum at 40 km ((Coeff)40 = 2.2) and additional maxima at 12 km ((Coeff)12 = 0.5), 23 km ((Coeff)23 = 0.9), and 50 km ((Coeff)50 = 1.1). In 1997, the number of events decreased to 64 with two intensity maxima at depths of 36 km ((Coeff)36 = 0.6) and 48 km (Coeff)48 = 0.8) (see **Figure 4**). Moreover, at a depth of 40 km, there was a clear decrease in seismic activity (Coeff)40 = 0.2.

Corresponding changes for the period 1994-01-01/1995-12-31 (**Figure 3**) also occurred in each of the studied sectors from 2 to 12, and an increase in the number of

#### **Figure 3.**

*The summed wavelet coefficients from scale level 1 to 32 for probability distributions* P*(Δ*h*) of earthquakes with energy class* KS ≥ *8.5 over depth intervals Δ*h *= 1 km for 1994 and 1995.*

#### **Figure 4.**

*The summed wavelet coefficients from scale level 1 to 32 for the probability distributions* P*(Δ*h*) of earthquakes with energy class* KS ≥ *8.5 over depth intervals Δh = 1 km for 1996 and for the period from 01.01.1997 to 12.04.1997. The triangle in sector № 8 marks two earthquakes on June 21, 1996 and July 18, 1996 (see text).*

events is characteristic of all sectors. The exceptions are sectors № 8, № 9, and № 12, for which the number of events decreased from 11, 12, and 4 in 1994 to 7, 8, and 3 in 1995. At the same time, a shift to shallow depths with increasing earthquake intensity occurred in 1995 in sectors № 4 (at zero depths with (Coeff)0 = 2.4) and №. 7 (at zero depths with (Coeff)0 = 1.8). In sector № 6, the intensity of events at shallow depths up *Investigation of the Dynamics of the Seismic Regime in the Kamchatka… DOI: http://dx.doi.org/10.5772/intechopen.109069*

to 20 km in 1994 slightly decreased compared to 1995. In sector 11, the intensity of events in 1994 was located at shallow depths from 0 to 10 km with a maximum at zero depth ((Coeff)0 = 4). In 1995, the intensity of earthquakes dropped sharply with the formation of a maximum at a depth of 40 km with (Coeff)0 = 2.2. It should be noted that for the period 1994-01-01/1995-12-31 at a depth of 40 km, distinct maxima of events of different intensity formed at a depth of 40 km in sectors 2, 3, 4, 7, 8, 10, and 12.

In 1996 (see **Figure 4**), an increase in the intensity of earthquakes at shallow depths up to 20 km clearly manifested itself in sectors № 6 ((Coeff)5 = 1.9) and № 8 ((Coeff)0 = 3). During this period, two earthquakes occurred in sector № 8, followed by aftershock activity with a total number of events *N* = 414:

• 1996-06-21.; *φ* = 51.27, λ = 159.63; *h* = 2 km, *K*<sup>S</sup> = 13.9; *M* = 6.2;

• 1996-07-18; *φ* = 51.22, *λ* = 159.82; *h* = 8 km, *K*<sup>S</sup> = 13.5; *M* = 6.0.

From 1996-01-01 to 1996-06-20 (before the earthquake of 1996-06-21), five seismic events with *KS* ≥ 8.5 occurred in sector № 8. From 1996-06-21 to 1996-07-17 (before the earthquake of 1996-07-18), there were 348 earthquakes with *KS* ≥ 8.5 (aftershock activity). After the earthquake of 1996-07-18, the aftershock activity in this sector sharply decreased, and until 1996-12-31, only 61 seismic events with *KS* ≥ 8.5 occurred. Seismic activity at a depth of 40 km decreased in 1997 in sectors № 1, 2, 4, 9, 11, 12.

Graphs of the summed wavelet coefficients calculated from the probability distributions *P*(Δ*h*), calculated for the entire area *S*Σ*,* which includes 12 regions, are shown in **Figure 4**. This figure shows the dynamics of changes in the intensity distributions of seismic events over the years, starting from 1994-01-01 and ending on 1997-12-04 (one day before the Kronotsky event). For comparison, **Figure 4** shows the distribution of seismic events averaged over the period of instrumental observations from 1962-01-01 to 2021-12-31 without taking into account the error in determining the depth of earthquakes. In this figure, for the average intensity plot 1962-01-01/2021- 12-31 at a depth of 40 km, the peak of seismic activity for the entire eastern coast is clearly distinguished, which is also distinguished for shorter periods of time (1994-01- 01/1997-12-31). In addition, **Figure 4** also shows less intense "petals" of averaged activity at depths of approximately 12, 18, 30, and 55 km, which, to one degree or another, repeat the "petals of activity" for 1994, 1995, 1996, and 1997 with large values of the wavelet expansion coefficients Coeff. This similarity indicates that in the lithosphere, at least along the studied area of the eastern coast of Kamchatka, there is a certain "fine" structure of zones of increased activity [13].

It follows from **Figures 3**–**5** that for 1994, starting from zero depths, the intensity of seismic events (numerical values of Coeff) decreases with increasing depth and merges with the averaged intensity of 1962-01-01/2021-12-31 obtained over the entire instrumental period of observation. Starting from 30 km, the intensity for 1994 exceeds the average. Over 1995, the intensity at shallow depths (from 0 to 10 km) becomes less than the intensity over 1994. In 1996, due to the earthquakes of 1996-06- 21 and 1996-07-18, and aftershock activity, the intensity of seismic events at shallow depths (from 0 to 15 km) exceeds the intensity for 1994 and 1995, remaining similar to the average intensity for the period of instrumental observations from 1962 to 2021-12-31. In 1997, the intensity at shallow depths decreases and practically merges with the intensity from 1994 to 1996 at depths greater than 35 km.

#### **Figure 5.**

*The summed wavelet coefficients from scale level 1 to 32 for the probability distributions* P(*Δ*h) *of earthquakes with energy class* KS ≥ *8.5 over depth intervals Δ*h *= 1 km for the* S<sup>Σ</sup> *region for the entire period of 1994, 1995, and 1996 and from 01.01.1997 to 04.12.1997. For comparison, the intensity distribution of seismic events for the period of instrumental observations from 01.01.1962 to 31.12.2021 is presented, against which events develop for the considered period of time 1994–1997.*
