The goal of this study is to determine whether principal component analysis (PCA) can be used to process latitude-time ionospheric TEC data on a monthly basis to identify earthquake associated TEC anomalies. PCA is applied to latitude-time (mean-of-a-month) ionospheric total electron content (TEC) records collected from the Japan GEONET network to detect TEC anomalies associated with 18 earthquakes in Japan (
Recent research into earthquake-associated ionospheric anomalies has been able to show that associations do exist between earthquakes and ionospheric disturbance [
2000 October 6 (04:30:19 UTC) | (35.45N 133.13°E) | Magnitude 6.7 (depth~10 km) |
2003 May 26 (09:24:32 UTC) | (38.90N 141.45°E) | Magnitude 7.0 (depth~68.2 km) |
2003 September 25 (19:50:06 UTC) | (41.775°N, 143.904°E) | Magnitude 8.3 (depth~27 km) |
2003 October 08 (09:06:55 UTC) | (42.658°N, 144.487°E) | Magnitude 6.7 (depth~32 km) |
2003 October 31 (01:06:28 UTC) | (37.829°N, 142.634°E) | Magnitude 7.0 (depth~10 km) |
2004 May 29 (20:56:12 UTC) | (34.256°N, 141.385°E) | Magnitude 6.5 (depth~38 km) |
2004 September 5 (10:07:07 UTC) | (33.062°N, 136.608°E) | Magnitude 7.2 (depth~14 km) |
2004 September 5 (14:57:18 UTC) | (33.184°N, 137.071°E) | Magnitude 7.4 (depth~10 km) |
2004 September 6 (23:29:35 UTC) | (33.184°N, 137.201°E) | Magnitude 6.7 (depth~10 km) |
2004 October 23 (08:56:00 UTC) | (37.226°N, 138.779°E) | Magnitude 6.6 (depth~16 km) |
2004 November 28 (18:32:13 UTC) | (42.995°N, 145.056°E) | Magnitude 7.0 (depth~39 km) |
2004 December 6 (14:15:11 UTC) | (42.907°N, 145.200°E) | Magnitude 6.8 (depth~35 km) |
2005 March 20 (01:53:41 UTC) | KYUSHU (33.805°N, 130.078°E) | Magnitude 6.6 (depth~10 km) |
2005 July 22 (07:34:57 UTC) | (35.506°N, 139.933°E) | Magnitude 6.0 (depth~65.6 km) |
2005 August 16 (02:46:28 UTC) | (38.251°N, 142.059°E) | Magnitude 7.2 (depth~36 km) |
2005 October 19 (11:44:43 UTC) | (36.383°N, 140.833°E) | Magnitude 6.4 (depth~41.5 km) |
2005 November 14 (21:38:51 UTC) | (38.101°N, 144.925°E) | Magnitude 7.0 (depth~11 km) |
2005 December 2 (13:13:09 UTC) | (38.122°N, 142.118°E) | Magnitude 6.5 (depth~29 km) |
This table shows the earthquakes (Richter magnitude ≥6.0) from 2000 to 2005 in Japan (Source: U.S. Geological Survey).
Location of GEONET receivers (red spot) and the epicenter of 18 earthquakes in Table
In the past, PCA has been widely used to detect and recognize the fine characteristics of signals; its physical meaning is indubitable [
The data used in this study is sourced from latitude-time vertical ionospheric TEC records from Japan’s GEONET network system for 18 earthquakes of M ≥ 6.0 that occurred in Japan from 2000 to 2005 (Table
Data records form a matrix of dimensions 24 (24 hrs) × 1200 (1200 receivers) (GEONET consists of ~1200 receiver); that is, from Formula 1,
In October 2000, a large earthquake of M = 6.7 was recorded for western Honshu. Figure
(a) shows the latitude-time TEC record in Japan for October 2000 (JST: Japanese Standard Time) (Unit: TECu). (b) shows 12 principal eigenvalues in 2000. Dates constitute the horizontal axis and corresponding eigenvalues are on the vertical axis. Peaks and troughs in eigenvalues have been plotted and graphed on a month-to-month basis to allow for interpolation. The largest principal eigenvalue is represented in October in which an earthquake occurred on October 6 (Table
(a) shows the latitude-time TEC records in Japan for 2003 (Unit: TECu). (b) shows 12 principal eigenvalues in 2003. Three larger principal eigenvalues are represented in May, September, and October in which four earthquakes occurred on May 26, September 25, October 8, and October 31 (Table
(a) shows the latitude-time TEC records in Japan for 2004 (Unit: TECu). (b) shows 12 principal eigenvalues in 2004. Five larger principal eigenvalues are represented in May, September, October, November, and December in which seven earthquakes occurred on May 29, September 5, September 6, October 23, November 28, and December 6 (Table
(a) shows the latitude-time TEC records in Japan for 2005 (Unit: TECu). (b) shows 12 principal eigenvalues in 2005. Six larger principal eigenvalues are represented in March, July, August, October, November, and December in which six earthquakes occurred on March 20, July 23, August 16, October 19, November 14, and December 2 (Table
A large earthquake occurred on Kyushu, Japan in March 2005. The corresponding TEC record is shown in Figure
(a) shows the TEC record in May 2005 (Unit: TECu) corresponding to the Kyushu earthquake of 20 March, 2005 M = 6.6 in Japan (Table
This study examines a relatively long time series of data from 2000 to 2005. Figures
The possibility that geomagnetic activity could have interfered with the results of this study is now examined. Figures
This figure denotes the Dst indices for year 2000 in Japan.
This figure denotes the Dst indices for year 2003 in Japan.
This figure denotes the Dst indices for year 2004 in Japan.
This figure denotes the Dst indices for year 2005 in Japan.
In this study, PCA is applied to latitude-time (mean-of-a-month) ionospheric total electron content records collected form the Japan GEONET system to detect TEC anomalies associated with 18 earthquakes in Japan (M ≥ 6.0) from 2000 to 2005. PCA was able to discriminate clear TEC anomalies in the months when all 18 earthquakes occurred, and such anomalies existed earlier than this 5-day statistical window. It is possible that these TEC anomalies are earthquake related after examining the Dst index for geomagnetic storm activity over this same period. Application of PCA to examine the Kyushu earthquake of 20 March, 2005 (M = 6.6) revealed a large principal eigenvalue representative of an earthquake-associated TEC anomaly 11 days before that earthquake on March 9. This result supports the integrity of the mean-of-a-month analysis.
The author is grateful to Dr Louis (L.Y.) Tsai of the Graduate Institute of Applied Geology and Dr H. W. Chen of the Institute of Geophysics, National Central University for their useful references and data support.