Association of Seismic Activity with Solar Cycle and Geomagnetic Activity

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Association of Seismic Activity with Solar Cycle and Geomagnetic Activity Tamara Gulyaeva Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, IZMIRAN, Kaluzskoe Sh. 4, Troitsk, 142190 Moscow, Russia gulyaeva@izmiran.ru Abstract The long-term relationship is investigated between the occurrence of earthquakes with magnitude from 5.0 to 10.0 (M5+), the solar cycle and geomagnetic activity for a period from 1964 to 2013. It is found that the global number of earthquakes tends to grow towards the solar cycle minimum characterized by the sunspot number, SSN, and solar radio flux F10.7. The trend of anti-correlation between the global earthquake occurrence and the phase of the solar cycle is expressed analytically in terms of SSN and F10.7 and applied for prediction of earthquakes number, EQN, based on SSN prediction. The occurrence of EQN in the South magnetic hemisphere relative to that in the North hemisphere is about 1.5 times greater the both irrespective of season. It is shown that zones of enhanced seismic activity are located in the Pacific Ocean at longitudes between 120 to 210E and magnetic latitudes from 40S to 40N with dominant earthquake occurrence in the sub-equatorial region of the South hemisphere. Taking advantage of monitoring the equatorial ring current variations with geomagnetic disturbance storm time Dst index, relevant catalogue of 1305 geomagnetic Dst storms during 1964-2013 is produced and compared with seismic activity. It is found that 13% of earthquakes M5+ occur during Dst storm times showing an enhanced seismic activity at the growing branch of phase of the solar cycle which is permanent feature of the geomagnetic activity.

Keywords Earthquake; Seismology; Solar Activity; Geomagnetic Storm

Introduction It is recognized that there are pre-earthquake phenomena comprised of the local magnetic field variations, electromagnetic emissions at the different frequency ranges, excess radon emanation from the ground, changes in water chemistry, water condensation in the atmosphere leading to haze, fog or clouds, atmospheric gravity waves rising up to the ionosphere, changes in the ionospheric Total Electron Content (TEC) and the F2 layer peak electron density

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(Gokhberg et al., 1983; Biagi et al., 2001; Hayakawa et al., 2010; Freund, 2013). The seismic-ionospheic theories and lithosphere–atmosphere–ionosphere models explain the earthquake-ionosphere coupling processes by electromagnetic wave propagation, acoustic gravity wave, atmospheric electricity and geochemical channel (Pulinets, 2009; Harrison et al., 2010; Namgaladze et al., 2012; Freund, 2013). The ionosphere precursors of earthquakes and the magnetosphere storm effects on seismic events are widely investigated (Pulinets and Boyarchuk, 2004; Liu et al., 2004; Zhao et al., 2008; Karatay et al., 2010; Namgaladze et al., 2012; Komjathy et al., 2013; Le et al., 2011, 2013; Pohunkov et al., 2013; He et al., 2014).

Though the earthquake affects the surrounding space within the restricted area (of 100 to 4,000 km radius), the prolonged effects and frequency of occurrence of the earthquakes may have cumulative effects on the ionosphere structure and variability (Rishbeth, 2006; Astafyeva et al., 2009; Gulyaeva et al., 2014a).

The solar electromagnetic radiation, particularly, at wavelengths of solar X-rays (XUV) is absorbed by the Earth’s upper atmosphere producing the ionosphere plasma. The XUV fluctuates regularly and irregularly over timescales from minutes (flares) and roughly 27 days (solar rotation) to decades (11-year solar cycle), with amplitudes varying up to more than 1000 times (Liu et al., 2011). Though it is difficult to distinguish between pure seismic precursors in the ionosphere from geomagnetic storm effects (Karatay et al., 2010; He et al., 2014), the post-earthquake phenomena are well observed and found over the local areas of high seismic activity providing opportunity to make study of both temporal and spatial earthquake-ionosphere associations (Rishbeth, 2006; Pohunkov et al., 2013).

While the ionosphere precursors and post-event effects of the particular earthquakes or series of seismic events has been intensely studied (Le et al., 2011; Namgaladze et al., 2012), a possible linkage of

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the Earth’s seismic activity with the long-term solar and geomagnetic activity has not been paid due attention. Empirical coupling of the earthquake occurrence with solar and geomagnetic activity is the subject of the present study.

Data Base The aim of the present study is to find out if there is a long-term coupling between the occurrence of the earthquakes of magnitude M = 5.0 to M = 10.0 and solar and geomagnetic activity. We use earthquake data from the global Catalogue of the Advanced National Seismic System (ANSS) provided by the Northern California Earthquake Data Center (NCEDS). The composite Catalogue of earthquakes created by ANSS is a world-wide earthquake catalog which is created by merging the master earthquake catalogs from contributing ANSS member institutions and then removing duplicate events, or non-unique solutions for the same event. We use the monthly and annual data sets from the Catalogue for a period from 1964 (start at the solar minimum of the 20th solar cycle) up to the end of 2013 (the peak of the 24th solar cycle). Total number of earthquakes M5+ for the selected period of 50 years is greater than 79,000 events which provide a good database for the statistical analysis. Relevant monthly mean and annual mean sunspot numbers (SSN) are downloaded from the National Geophysical Data Center and the solar 10.7 cm radio flux index (F10.7) is provided by Space Weather Canada service.

In this paper the statistical study has been performed to analyze the relation of the earthquake occurrence with geomagnetic storms identified with the disturbance storm time, Dst, index (Sugiura and Kamei, 1991). The Dst index is taken as an indicator of Sun’s induced geomagnetic disturbed conditions, as it represents the depressions in the ring current as a result of its interaction with the plasma signatures having their roots originated at the solar surface (Gonzalez et al., 1994). Our Catalogue of Dst storms for the period 1964-2013 is composed according to proposed criteria (Gulyaeva et al., 2014b) from Dst index provided by the World Data Center for Geomagnetism, Kyoto, Japan.

Results The

annual

number

of

earthquakes

(EQN)

of

magnitude M5+ and the annual SSN are plotted in Fig. 1. The signatures of the anti-phase variation of the earthquake occurrence and the sunspot numbers can be captured from Fig. 1 suggesting that the seismic activity could be enhanced near the solar minimum, particularly, during the recent 23rd solar cycle. The solar activity during 2007–2009 was extremely low and one of the longest recent solar minima. An extreme EQN occurrence is seen for this period exceeding that for the preceding solar minima.

FIG. 1 TIME SERIES OF ANNUAL NUMBER OF EARTHQUAKES M5+ SUPERIMPOSED BY THE SUNSPOT NUMBER SSN CURVE

Fig. 2 presents the occurrence of monthly SSN, monthly mean solar radio flux F10.7 and earthquakes number, EQN, versus the phase  of the solar cycle (Gulyaeva and Stanislawska, 2008):  = (T − m)/(M − m)

(1)

Here T is the month for a parameter under consideration (fractional year monthly number, e.g.

2013.9), m is the month of the solar minimum, M is the month of the solar maximum (the pair of m and M embracing the parameter).  = 0 for solar minimum,  = 1 for solar maximum.

The median of SSN, F10.7 and EQN is obtained in ten bins of  = 0.1 and median of EQN is plotted against the median of SSN (red) and median of F10.7 (blue) in Fig. 2d. The scatter of individual monthly EQN in Fig. 2c exhibits influence of other factors in addition to the solar activity affecting the EQN occurrence.

The relevant functional dependence of EQN on SSN (Eqn. 2) and EQN on F10.7 (Eqn. 3) is expressed according to results shown in Fig. 2d: EQN = 138.18 – 0.1832 SSN

(2)

EQN = 151.28 – 0.2063F10.7

(3)

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FIG. 2 MONTHLY NUMBER OF (a) SSN, (b) F10.7 AND (c) EQN M5+ AGAINST PHASE OF THE SOLAR CYCLE; (d) RELATION OF MEDAN EQN() WITH SSN() AND F10.7(). ALL DATA POINTS AND RESULTS OF LEAST SQUARE FITS FOR 1964-2013

Using prediction of the 12-months’ smoothed SSN available for 2014 to 2020, Eqns. 1-3 could be applied for EQN prediction up to the end (forthcoming minimum) of the current 24th solar cycle (SSN-min is foreseen in August, 2019, as it is predicted on April, 2014). Results of the annual number of EQN prediction based on Eqns. 1-2 are provided in Table 1.

TABLE 1 PREDICTIONS OF ANNUAL EQN M5+ FOR THE 24TH SOLAR CYCLE BASED ON EXPECTED SSN (PREDICTION OF NGDC ON APRIL, 2014)

Year 2014 2015 2016 2017 2018 2019

SSN 69.1 53.0 38.2 24.7 14.4 9.2

EQN 1506 1542 1574 1604 1627 1638

The coordinates of EQ M5+ epicenters have been separated by the magnetic equator for the North and South magnetic hemispheres and monthly EQN in the North and South magnetic hemispheres are calculated (Fig. 3). Clear evidence of the long-term excess of M5+ events occurrence by 1.5 times is observed in the South magnetic hemisphere as compared with the North hemisphere. The total set of EQN does not reveal a seasonal dependence as can be seen in Fig. 3.

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FIG. 3 PERCENTAGE OCCURRENCE OF MONTHLY NUMBER OF EQ M5+ EVENTS IN THE NORTH AND SOUTH MAGNETIC HEMISPHERES

Analysis of global distribution of epicenters of EQs M5+ reveals zones of enhanced seismic activity in the Pacific Ocean at longitudes from 120 to 210E and magnetic latitudes from 40S to 40N with dominant earthquake occurrence in the sub-equatorial region of the South hemisphere (Fig. 4). Here EQN M5+ in the particular area of a globe is calculated relative to the total number of EQN in the database. The area of the enhanced seismicity in the South magnetic hemisphere relative to that in the North hemisphere is about 1.5 times greater congruent with results of Fig. 3.

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EQN set including both the magnetic storm and nonstorm conditions is provided in Fig. 5 reminding results of Fig. 2c. In general, the storm time EQN shows congruent growth towards the peak of the solar cycle as distinct from the total set of EQN with the anti-phase solar trend.

Conclusions

FIG. 4. ZONES OF ENHANCED SEISMIC ACTIVITY FOR PERCENTAGE OF EQN M5+ REGARDING THE TOTAL DATA SET FOR 1964-2013. TECTONIC PLATES BOUNDARIES (BOLD WHITE) AND MAGNETIC LATITUDES MLAT (DASHED WHITE) ARE ALSO SHOWN.

Keeping in mind the dominant occasions of EQN in the sub-equatorial magnetic zone, we proceed to comparison of EQN occurrence with the geomagnetic storms observed in the equatorial zone. Fortunately, monitoring the equatorial ring current variations with geomagnetic disturbance storm time Dst index allows us to produce Catalogue of 1305 geomagnetic storms during 1964-2013 (Gulyaeva et al., 2014b) and select relevant EQN events during the storm hours. It is found that 13% of earthquakes M5+ occur during the Dst storm periods.

FIG. 5 HISTOGRAM OF OCCURRENCE, IN PERCENT, OF THE TOTAL SET OF EQN M5+ FOR 1964-2013 VERSUS PHASE OF THE SOLAR CYCLE (BLUE), SUB-SET OF EQN M5+ DURING DSTSTORM PERIODS (BROWN), AND HOURS OF DST STORM TIMES (YELLOW) FOR 1964-2013

The results of histogram demonstrated in Fig. 5 shows the seismic activity enhanced at the growing branch of phase of the solar cycle ( = 0.4 to 0.8) when the dominant geomagnetic storms activity is routinely observed (Triskova, 1989; Gonzalez et al., 1994). For a comparison, the histogram of occurrence of the total

Clear evidence of the solar activity modulation of the earthquakes occurrence is demonstrated in the present study. The anti-correlation of seismic activity with solar activity is observed for a period of observations from 1964 to 2013 by referring the monthly earthquake M5+ occurrence to the phase of the solar cycle. This trend is opposite to the upper atmosphere density and the ionosphere plasma density and total electron content which follow closely to the solar activity (Kane, 1992; Liu et al., 2011). The monthly number of earthquakes, EQN M5+, is decreasing with growing solar cycle phase, , varying from  = 0 for solar minimum to  = 1 for solar maximum. The EQN varies in counter-phase with solar activity which means the EQN occurrence increased towards the solar minimum. This trend is described analytically by regression of median EQN() on sunspot number, SSN(), and the solar radio flux, F10.7(). The trends of anti-correlation of seismic activity with characteristics of solar activity is used for prediction of expected annual EQN based on SSN prediction for the current 24th solar cycle which is expected to vary from maximum (December, 2013) to minimum (August, 2019).

The coordinates of earthquake epicenters have been separated by the magnetic equator for the North and South magnetic hemispheres and monthly EQN in the North and South magnetic hemispheres are calculated.

The occurrence of EQN in the South magnetic hemisphere relative to that in the North hemisphere is about 1.5 times greater. The North-South asymmetry well established in the ionosphere may be affected by asymmetry in the seismic activity (Rishbeth, 2006; Gulyaeva at al., 2014b). At the same time there is no appearance of a seasonal variation in the both hemisphere’s EQN while the geomagnetic activity and plasma density in the ionosphere are systematically enlarged during the equinoxes (Triskova, 1989; Lal, 1998; Qian et al., 2013).

Analysis of global distribution of epicenters of EQs M5+ reveals zones of enhanced seismic activity in the Pacific Ocean at longitudes from 120 to 210E and

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magnetic latitudes from 40S to 40N with dominant earthquake occurrence in the sub-equatorial region of the South hemisphere. The next important zones of seismic activity are located in the South America and Middle East. The area of the enhanced seismicity in the South magnetic hemisphere relative to that in the North hemisphere is about 1.5 times greater confirming results of separation of EQN in the North and South magnetic hemispheres.

According to dominant location of EQs around the magnetic equator zone, we have produced catalogue of 1305 geomagnetic Dst storms during 1964-2013 using the data of the geomagnetic disturbance storm time, Dst, index based on monitoring the equatorial ring current variations. Comparison of seismic activity with Dst storm times reveals 13% of total set of earthquakes M5+ occurring during Dst storm times. It is found that an enhanced seismic activity is observed at the growing branch of phase of the solar cycle well identified for the geomagnetic activity (Gonzalez et al., 1994). Hence, general trends of the EQN and Dst storm variation at the growing branch of the solar cycle confirm seismic-geomagnetic associations. Separation of seismic and geomagnetic storm effects on the ionosphere variability (Pulinets and Boyarchuk, 2004; Karatay et al., 2010) deserves further attention.

ACKNOWLEDGMENTS

Catalogue of the Advanced National Seismic System (ANSS) is provided by the Northern California Earthquake Data Center (NCEDS) at http://www.nceds.org/anss/anss-detail.html.

The sunspot number is provided by the US National Geophysical Data Center at ftp://ftp.ngdc.noaa.gov/STP/space-weather/solardata/solar-indices/sunspot-numbers/. Solar F10.7 radio flux data are provided by Space Weather Canada service at ftp://ftp.geolab.nrcan.gc.ca/data/solar_flux/.

The Dst index is provided by WDC for Geomagnetism at http://wdc.kugi.kyoto-u.ac.jp/dstdir/index.html.

Catalogue of Dst storms is provided at http://www.izmiran.ru/services/iweather/storm/. This study is supported by the joint grant from RFBR 13-0291370-CT_a and TUBITAK 112E568 project.

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