Application of the seismic interferometry method for studying the earth’s inner core

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For a more detailed description of the dynamic processes and determination of the properties of the inner core regions, inaccessible to study by traditional methods, the seismic interferometry method, which is based on the technique of cross-correlation analysis of time series for different types of data, was applied in this work. Cross-correlation analyses of the seismic coda window with a start three hours after a strong event and the end 10 hours later are performed for all possible pairs of more than 300 stations and 6 large earthquakes (for each separately) occurring between 2013 and 2024. Synthetic cross-correlograms are calculated for models with different attenuation and an additional boundary in the inner core. Four different types of inner core studies by seismic interferometry were carried out: global, regional, station latitude-dependent, and calendar time-dependent. The stability of the PKIKPPPKIKP wave on global correlograms, the possibility of its observation in areas with high and low density of seismic stations, the dependence of the wave travel time on the angle between the wave direction and the Earth rotation axis, and the stationarity of the wave for the time period from 2013 to 2024 were demonstrated.

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Sobre autores

O. Usoltseva

Sadovsky Institute of Geospheres Dynamics of Russian Academy of Sciences

Autor responsável pela correspondência
Email: kriukova@idg.ras.ru
Rússia, Moscow

V. Ovchinnikov

Sadovsky Institute of Geospheres Dynamics of Russian Academy of Sciences

Email: ovtch@idg.ras.ru
Rússia, Moscow

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2. Fig. 1. Scheme of rays of waves I2 (a) and I4 (b) for an epicentral distance of 40°: 1 – inner core, 2 – outer core, 3 – mantle.

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3. Fig. 2. Synthetic correlograms based on the ak135PS models (a), (b), ak135S (c), (d), ak135 without taking into account the attenuation of body waves (d), (e). For sources with a depth of 50 km (left) and 500 km (right). Filtering in the period band of 15–50 s, coda duration of 10000–35000 s. The dotted line is the theoretical hodograph of the I2* wave.

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4. Fig. 3. Correlograms for the ak135PS model, source depth 50 km, filtering in the period band of 15–50 s, coda duration 10000–20000 s (a) and 20000–30000 s (b).

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5. Fig. 4. Correlograms for the ak135PS model, source depth 50 km, coda duration 10000–35000 s. Period ranges 10–30 s (a) and 30–60 s (b).

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6. Fig. 5. Correlograms for test models with IMIC (a) and without IMIC (b).

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7. Fig. 6. Earthquakes 1–3 from Table 1 (red stars) and stations (triangles) used: (a) networks II, IU, G, GE; (b) US Array (USA); (c) F-net (Japan); (d) networks II, IU, G, GE in Europe; (e) networks II, IU, G, GE, HE, FN north of 60° latitude. Red rectangles, and line (a) in the north, delimit the areas of the presented regional studies.

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8. Fig. 7. Fragments of correlograms with wave I2* based on data from various earthquakes: (a) 05/24/2013; (b) 01/22/2024; (c) 03/23/2024.

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9. Fig. 8. Top — distribution of the number of stations depending on the epicentral distance with a step of 0.5° in (a) and (b) and 2° in (c) and (d). Bottom — fragments of correlograms with the I2* wave based on data from the earthquake of 24.05.2013 and stations: (a) US Array; (b) F-net; (c) networks II, IU, G, GE in Europe; (d) networks II, IU, G, GE, HE, FN north of latitude 60°.

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10. Fig. 9. Distribution of the number of stations depending on the epicentral distance with a step of 2.0° (top) and fragments of correlograms with the I2* wave (bottom) based on data from the earthquake of 24.05.2013 for polar stations (a), mid-latitude (b) and equatorial (c).

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11. Fig. 10. Fragments of correlograms with the I2* wave based on data from earthquakes in 2013, 2017, 2021, 2024 and the F-net seismic network.

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