Research on the Earthquake and Volcanic Disaster Chain System in Indonesia

1. Preface

The impact area of the world's 16^#th Indonesia Seismic Cone Tectonic (SCT for short) is located between 85°～138°E and -16°～10°N, as shown in Figure 1. The Indonesian SCT is one of the global deep-focus seismic cone tectonics, with a maximum focal depth of 675 km, and it is also one of the most active seismic cone tectonics in terms of intra-crustal strong earthquakes and volcanic eruptions in the world.

Based on the principles and working methods of the Seismo-Geothermics Theory created by the author [1,2,3,4,5,6,7,8], this paper aims to explore the relationship between intra-crustal strong earthquakes, volcanic eruptions and the seismic cone tectonic in the study area, and attempts to establish a prediction model for disaster events, namely the disaster chain of intra-crustal strong earthquakes and volcanic eruptions. It may be beneficial to the accumulation of experience in the prediction of global earthquake and volcanic disaster events and bring benefits to mankind.

2. Materials and Working Methods

The seismic data of the study area comes from the ANSS earthquake catalog of the Southern California Earthquake Center (USA). A total of 82,390 earthquakes with a magnitude of 4.0 or higher in the study area from 1963 to May 8, 2025 were obtained, and the distribution of the sub-crustal strata is shown in Table 1. Based on the three-dimensional distribution of seismic activity in this area, 7 research sub-areas, namely Inn A to Inn G, were divided, which are 7 sub-SCTs, as shown in Figure 1. These sub-cone tectonic have different shapes, each with its own unique three-dimensional morphology (Figure 2) and a disaster chain system (DCS for short, see Figure 3) where intra-crustal strong earthquakes, volcanic eruptions, and sub-crustal earthquakes coexist, thus having special research significance.

The earthquake and volcanic disaster chain system is composed of geological elements such as sub-crustal earthquakes (earthquakes with a focal depth greater than 35 km) within the SCT, strong intra-crustal earthquakes (with a depth less than 35 km, M 7.0+ or M 6.5+), surface seismogenic structural systems (torsional structures, thrust structures, etc.), habitual or newly formed volcanic channels, and so on.

The influence area of a sub-cone (sub-SCT) is not a fixed block; its range can be larger or smaller depending on the research objectives, but the core cone area remains unchanged. The core of the sub-SCT is dominated by sub-crustal earthquakes, rather than determined by surface seismic images. The most refined sub-SCT is a single sub-cone structure, which has an independent activity pattern and is not disturbed by adjacent sub-cone structures.

This paper adopts the traditional working method of the Seismo-Geothermics, that is, using the time series diagram of sub-crustal earthquakes to track the correlation between strong intra-crustal earthquakes and volcanic eruption events, and to find prediction models. At the same time, this paper uses Fourier spectrum analysis in the hope of finding some correlation between the earthquake and volcanic disaster chain and the Earth's nutation.

3. Sub-SCTs of the Indonesian SCT

Based on the three-dimensional images of Indonesia's SCT, this paper roughly divides 7 research zones, namely Inn A to Inn G, which are 7 seismic sub-cone structures, after multiple screenings. Since the In A sub-cone structure involves parts of the Philippines and the data is incomplete, it is not included in the research scope of this paper. Therefore, this paper focuses on the study of 6 seismic sub-cone structures from Inn B to Inn G.

The stratigraphic activity parameters of each sub-cone structure are shown in Table 2, the parameters of M 7.0+ intra-crustal strong earthquake activities from 1963 to 2025 are shown in Table 3, and the parameters of volcanic eruptions with a Volcanic Explosivity Index (VEI) of 3+ are shown in Table 4.

It can be seen from these data tables that each of the 6 sub-cone structures forms an independent disaster chain of intra-crustal strong earthquakes and volcanic eruptions. There are only 4 such regions with intense consecutive disaster chains in the world. In addition to Indonesia, they are the western Pacific (from the Okhotsk Sea to the Mariana Trench), the southwestern Pacific (from the Solomon Islands to Tonga and New Zealand), and the western coast of South America (Ecuador and Chile). These places are the best sites for us to explore the causes and prediction models of intra-crustal strong earthquakes and volcanoes.

The time series diagrams of sub-crustal seismic activities for each sub-cone structure are shown in Figure 4, Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9. It can be seen from the figures that before 1975, the resolution of sub-crustal earthquake data in each sub-cone study area was relatively low, and the situation did not improve significantly until the mid-1980s. Therefore, the time period available for the study of annual seismic conditions is very limited. A short history of just over 40 years can only be regarded as a moment in both seismology and geology.

3.1. Concept and Definition of Annual Seismic Activityε₀(t)

The dense seismic zone beneath the crust is an obvious sign of the structure of the seismic cone. The Seismo-Geothermics theory holds that all global events, such as strong intra-crustal earthquakes, volcanic eruptions, climate warming or cooling, etc., are related to the thermal movement in the deep upper mantle. Therefore, it is very important to investigate the activity intensity of sub-crustal earthquakes within deep seismic active structures.

The simplified Gutenberg (Gutenberg et al., 1956) relationship between the seismic wave energy E released by an earthquake and the earthquake magnitude M is as follows (the unit of energy E is erg):

Lg E=11.8+1.5Ms

(1)

Then the Benioff strain energy √E has

Lg √E=5.9+.75Ms

(2)

To avoid confusion regarding the unit of measurement for energy E and excessively large data volumes, it is advisable to convert √E into the number of M 4.0 earthquakes for annual accumulation. Then, the annual cumulative value E (t) is

$$\mathrm{E}\left(\mathrm{t}\right)={\sum }_{\mathrm{i}=0}^{\mathrm{n}-1}{10}^{\left(.75{\mathrm{M}}_{\mathrm{i}}-3\right)} i=0，1，2\dots n-1；t=1963-2025$$

(3)

In the formula, t represents the statistical year, among which the data for the last year, 2025, is incomplete and is for reference only. n is the total number of subshell earthquakes in that year. The annual anomaly normalized ratio ε ₀(t) of E (t) can be obtained from formula (3), which is as follows:

$${\mathsf{\epsilon }}_0\left(\mathrm{t}\right)=\left(\mathrm{E}\right(\mathrm{t})-\mathrm{͞}\mathrm{E}\_0)/(\mathrm{͞}\mathrm{E}\_0)\hspace{1em}\mathrm{t}=1963-2025$$

(4)

In the formula, E0 is the multi-year average value of E (t).

The average value of the ratio ε₀ is 0. The annual ratio ε₀ integrates the comprehensive effects of earthquake frequency N, magnitude M, and the strain energy released by earthquakes, and can comprehensively represent the activity intensity of sub-crustal earthquakes, so it is defined as the sub-crustal seismic activity. To examine the conditions of formations at different depths, the seismic activity of each target formation can be calculated.

Formula (3) is applicable regardless of whether the minimum magnitude of the earthquake catalog is M 1.0 or M 4.0, or whether the time window is annual or 0.1a. Of course, it is required that the earthquake catalog provides time series coordinates in annual units.

ANSS is originally a composite earthquake catalog that uses multiple magnitude scales. As a first-order approximation, all earthquake magnitudes in this paper are regarded as Ms.

3.2. Detailed Description of Seismic Conditions in Each Sub-Cone Study Area

The seismic and volcanic conditions of the study areas in sub-cones InB to InG are described separately as follows:

3.2.1. Inn B Sub-Cone Study Area

The Inn B sub-cone is located in the area east of East Kalimantan Province, Indonesia. Since the 1980s, intra-crustal strong earthquakes and volcanic eruptions have alternated, making it extremely active. See Figure 4 for details. There were successive strong intra-crustal earthquakes with a magnitude of 7+ between 1998 and 2008, and successive volcanic eruptions with a VEI of 3+ between 1982 and 1991 as well as between 2002 and 2025. The analysis shows that the continuous rising segment of the annual activity level ε₀ (t) of sub-crustal earthquakes (marked by the blue arrow line) and the high differential value of the activity level have certain precursory significance for both intra-crustal strong earthquakes and volcanic eruptions. If the local Indonesian earthquake catalog of M 1.0+ to M 3.0+ can be used, this precursory significance will only increase rather than decrease.

Figure 4. Time series diagram and analysis of the Inn B sub-SCT of the Indonesian SCT. Explanation of Figure 4: The egg-yellow dots represent M 4.0-4.9 earthquakes, the green dots represent M 5.0-5.9 earthquakes, the blue dots represent M 6.0-6.9 earthquakes, the orange dots represent M 7.0+ earthquakes, the red dots represent M 7.0+ strong intra-crustal earthquakes, and the red triangles represent VEI 3+ volcanic eruptions. (The same below).

Figure 4. Time series diagram and analysis of the Inn B sub-SCT of the Indonesian SCT. Explanation of Figure 4: The egg-yellow dots represent M 4.0-4.9 earthquakes, the green dots represent M 5.0-5.9 earthquakes, the blue dots represent M 6.0-6.9 earthquakes, the orange dots represent M 7.0+ earthquakes, the red dots represent M 7.0+ strong intra-crustal earthquakes, and the red triangles represent VEI 3+ volcanic eruptions. (The same below).

3.2.2. Inn C Sub-Cone Study Area

The Inn C sub-cone is located in the eastern part of the Banda Sea, Indonesia. Since the 1980s, strong intra-crustal earthquakes and volcanic eruptions have occurred alternately, with an interval of about 10 years. See Figure 5 for details.

Figure 5. Time series diagram and analysis of the Inn C sub-SCT of the Indonesian SCT.

Figure 5. Time series diagram and analysis of the Inn C sub-SCT of the Indonesian SCT.

3.2.3. Inn D Sub-Cone Study Area

The Inn D sub-cone is located in the core area of the western Banda Sea, Indonesia, where strong intra-crustal earthquakes and volcanic eruptions occur alternately, with an interval of about 10 years, and the longest interval can reach 18 years. See Figure 6 for details.

Figure 6. Time series diagram and analysis of the Inn D sub-SCT of the Indonesian SCT.

Figure 6. Time series diagram and analysis of the Inn D sub-SCT of the Indonesian SCT.

3.2.4. Inn E Sub-Cone Study Area

The Inn E sub-cone is located in the West Nusa Tenggara Province of Indonesia, where strong intra-crustal earthquakes and volcanic eruptions occur alternately, with an interval of about 10 years, and the longest interval can reach 20 years. The most powerful Agung Volcano (VEI 5) in Indonesia in recent years is located in this area. See Figure 7 for details.

Figure 7. Time series diagram and analysis of the Inn E sub-SCT of the Indonesian SCT.

Figure 7. Time series diagram and analysis of the Inn E sub-SCT of the Indonesian SCT.

3.2.5. Inn F Sub-Cone Study Area

The Inn F sub-cone is located in the Java Island region of Indonesia, where strong intra-crustal earthquakes and volcanic eruptions occur alternately, with an interval of about 10 years, and the longest interval can reach 15 years. There were successive VEI 3+ volcanic eruptions between 2010 and 2020. Eruptions of volcanoes such as Semeru and Tengger can last for several months or even years. See Figure 8 and Table 4 for details.

Figure 8. Time series diagram and analysis of the Inn F sub-SCT of the Indonesian SCT.

Figure 8. Time series diagram and analysis of the Inn F sub-SCT of the Indonesian SCT.

3.2.6. Inn G Sub-Cone Study Area

The Inn G sub-cone includes the entire island of Sumatra, Indonesia, where intense intra-crustal earthquakes and volcanic eruptions occur alternately, with an interval of about 10 years. Since 2000, intra-crustal earthquakes of magnitude 7+ and volcanic eruptions of VEI 3+ have occurred alternately in succession. Eruptions of volcanoes such as Sinabung, Krakatoa, and Karangetang can last for months or even years. See Figure 9 and Table 4 for details.

Unfortunately, more precursor information about the 2004 Indonesian M 9.2 earthquake could not be found in this figure, and it may be necessary to rely on Indonesia's local earthquake catalogs of M 1.0+ or M 2.0+.

Figure 9. Time series diagram and analysis of the Inn G sub-SCT of the Indonesian SCT.

Figure 9. Time series diagram and analysis of the Inn G sub-SCT of the Indonesian SCT.

4. Discussion

4.1. Discussion on the Disaster Chain System

It is found through the research in this paper that each individual SCT or sub-SCT can form an independent disaster chain system of strong intra-crustal earthquakes and volcanic eruptions. The disaster chain system independently expresses the interrelationships between sub-crustal earthquakes, strong intra-crustal earthquakes, volcanic eruptions and the surface tectonic system within the SCT. When there is no volcanic activity in the SCT, it only forms a strong intra-crustal earthquake disaster chain system. The disaster chain system is a working platform for studying the causes of earthquakes and volcanoes and their prediction models. The global M 4.0+ earthquake catalog may only yield rough evaluation results, while local earthquake catalogs of M 1.0+ or M 2.0+ are conducive to more detailed research. Therefore, in each seismically and volcanically active area, efforts should be made to strengthen research on earthquake catalog compilation techniques, strive to improve the resolution capability of sub-crustal earthquakes, and it is best to form unified global compilation standards. The proportion of sub-crustal earthquakes must reach more than 20% to meet the basic requirements for the analysis of the Seismo-Geothermics theory.

4.2. Relationship Between the Disaster Chain System and the Surface Tectonic System

In this study, we are fortunate to discover the subtle relationship between sub-crustal seismic activity and the surface tectonic system. The Sumatra Fault in Figure 1 should be attributed to the Yunnan's zigzag-shaped tectonic structure system, a right-lateral strike-slip fault. It can be seen from Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9 that along the sub-crustal seismic activity of this fault zone, the focal depth increases continuously from west to east. East of Java Island, the maximum focal depth stabilizes at over 600 km. What's more, the duration of volcanic eruptions along this fault zone gradually changes from several months or even years in the west to several days in the east. The strongest VEI 5 volcanic eruptions in this region occur in the area with the maximum focal depth.

It can be inferred from this that the seismic activity beneath the crust is not unrelated to the surface tectonic system.

4.3. The Issue of the Activity Cycle of the Driving Layer

The activity cycles of the driving layer in Figure 4, Figure 6, and Figure 8 show an obvious interval of about 18 years. It is speculated that sub-crustal seismic activity may be related to the nutation of the Earth, so an attempt was made to conduct a spectrum analysis of sub-crustal seismic activity. The results show that the spectrum analysis can only detect short cycles of several years, but no cycle components longer than 10 years, which may be due to the limited length of the sample size.

This paper raises this doubt for reference by future researchers.

4.4. The Continuous Rising Period of Activity from 2000 to 2024

As can be seen from Figure 4, Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9, the energy activity of sub-crustal earthquakes is closely related to strong intra-crustal earthquakes and volcanic eruptions. This is the real reason for the frequent occurrence of these two disasters.

Since 2000, the sub-crustal seismic activity in the entire study area has been in a continuous rising state, which changes synchronously with global warming [9]. Synchronously, strong intra-crustal earthquakes and volcanic eruptions in Indonesia have been extremely active, especially in the area east of East Kalimantan Province and on Sumatra Island. This situation will take a long period to relieve, so the assessment or prediction of disasters is very important.

As can be seen from Figure 2, the sub-cone structure in the Indonesian study area can be further divided into several sub-columns. For this reason, it is necessary to use a more refined local seismic catalog of Indonesia to accurately map strong intra-crustal earthquakes and volcanic eruptions to each individual sub-cone structure for tracking and prediction research.

In Figure 9, before the 2004 M 9.2 earthquake in Indonesia, there was only a small rising segment of about 6 years in the sub-crustal seismic activity curve, which seems not to match the major earthquake. This may be related to the monitoring capacity of earthquakes, or it may be necessary to conduct tracking research based on Indonesia's local seismic catalog.

5. Conclusion

Based on the author's self-developed theoretical system of the Seismo-Geothermics theory, this paper uses the M 4.0+ earthquake catalog of Indonesia from the California Earthquake Center in the United States to determine the geographical distribution and three-dimensional spatial distribution characteristics of earthquakes and volcanoes in the study area, according to the concept of Seismic Cone Tectonic divides 7 sub-SCTs, formulates a holographic ideal model of SCT, and defines two concepts: the disaster chain of intra-crustal strong earthquakes and volcanic eruptions, and the annual activity of sub-crustal earthquakes of SCT. For the 6 sub-cone structures directly related to the Indonesian study area, temporal image analysis, annual analysis and differential analysis of activity are carried out. On this basis, a prediction model and research plan for intra-crustal strong earthquakes and volcanic eruptions are formulated, which can be used as a reference for the research on deep-source seismic cone structures in the Indonesian region, the Western Pacific region, the Southwest Pacific region, and the west coast of South America.

At present, people's understanding of the causes of intra-crustal strong earthquakes and volcanic eruptions is still in the realm of necessity in epistemology. They always think that M 7, M 8 or even M 9 intra-crustal strong earthquakes or volcanoes can be brewed by the accumulation of strain energy from surface tectonic movements or the pushing and squeezing of large and small blocks. Little do they know that such strong earthquakes and volcanic eruptions require the accumulation, storage and instantaneous release of energy at a celestial level, and only some kind of force from the overall movement of the Earth can such a miracle be created. Without realizing this, it will always be difficult to enter the realm of freedom.

In order to find such a force, the author has struggled hard all his life, hoping that hard work will be rewarded.