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Table 1 Comparison of phenomena associated with slip event at deep portion along the plate interface. - 457 -
ECMJMA LFE 3 8 29 31 3 2-16Hz ECM Fig.1 Comparison of detection capability as tremor by ECM and low-frequency earthquake by JMA from the same envelope seismograms of tremors. The envelopes are RMS traces from the band-pass filtered waveforms with a pass band of 2-16 Hz observed at 4 stations in western Shikoku. The red and blue circles are detected tremors by ECM and lowfrequency earthquake by JMA, respectively. - 458 -
(a)ecm 1 7.5km 1km AB,CD Shiomi et al.12) km (b) 1 7 Fig.2 (a) Epicentral distribution of tremor by ECM catalog from 1 to 7. Red and orange dots are epicenters of tremors located with error within.5 km and 1 km, respectively. The dotted rectangle AB and CD are indicated in Fig.4. Blue lines are depth contours of oceanic Moho discontinuity in the Philippine Sea plate estimated by Shiomi et al.(8) 12) (unit:km). (b) Epicentral distribution of low-frequency earthquake by JMA catalog from 1 to 7. - 459 -
(a)cmt 1 8 ECM 1km (b) 1 8 EF (b) Fig.3 (a) Epicentral distribution and focal mechanism of deep very-low-frequency earthquake by CMT analysis from 1 to 8. Red dots are epicenters of tremors located with error within 1 km. Blue lines are depth contours of oceanic Moho discontinuity in the Philippine Sea plate estimated by Shiomi et al. 12) (unit:km). (b) Location of fault planes of shortterm slow slip events detected and estimated by NIED tiltmeters from 1 to 8. The bold line of each rectangle indicates the shallower side of the fault plane. All fault models are reverse fault type and are located at around the plate interface. Doted lines of E-F indicates the profile for the space-time plot in Fig.4(b). - 46 -
(a) AB,CD ECM 7 (b) SSE SSE 2cm 1cm Fig.4 (a) Frequency distribution of tremors, low-frequency earthquakes and very low-frequency earthquakes along the profile of A-B and C-D indicated in Fig.2. The tremors by ECM catalog, low-frequency earthquakes from the JMA catalog, and very low-frequency earthquakes from the CMT analysis with a duration from 1 to 7 are plotted. (b) Spacetime distribution of slip amount of the slow slip event along the profile of E-F indicated in Fig.3. The bold line of each rectangle indicates the origin time of the slow slip event and the width indicates the slip amount. - 461 -
Fig.5 Spacetime distribution of tremors from ECM catalog (left) and low-frequency earthquakes from the JMA catalog (right) plotted by red dots. Blue diamonds are very low-frequency earthquakes, which have been analyzed from April, 3. - 462 -
SSE SSE SSE (6) 13) SSE Fig.6 Spacetime distribution of slow slip events plotted on the tremors. Blue rectangles are large-size slow slip events with fault parameters estimated from tilting data. Green rectangles are small-size slow slip events with fault parameters not estimated whereas associated with the tilt step detected by only a few stations. Yellow rectangles are slow slip events in Tokai area estimated by strainmeters by the JMA by Kobayashi et al.(6) 13). - 463 -
3 1 1 2 8 3 4 44 4 12 Fig.7 Time interval between the sequential tremor episodes in the three segments in Shikoku. The horizontal axis is the sequential number of the tremor episode from January 1. The red dotted rectangle indicates affection by the long-term slow slip event in the Bungo Channel. - 464 -
Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] Daily frequency [NIED ECM Tremor Catalog] ECM Fig.8A Daily frequency of tremors from the ECM catalog. - 465 -
Daily frequency Daily frequency Daily frequency Daily frequency Daily frequency Daily frequency Daily frequency [JMA LFE Catalog] [JMA LFE Catalog] [JMA LFE Catalog] [JMA LFE Catalog] [JMA LFE Catalog] [JMA LFE Catalog] [JMA LFE Catalog] Fig.8B Daily frequency of low-frequency earthquakes from the JMA catalog. - 466 -
ECM 12ECM VLF Fig.9A Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in western and central Shikoku with a time window of 12 days. - 467 -
ECM 12ECM VLF Fig.9B Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in western and central Shikoku with a time window of 12 days. - 468 -
ECM 12ECM VLF Fig.9C Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in western and central Shikoku with a time window of 12 days. - 469 -
ECM 12ECM VLF Fig.9D Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in western and central Shikoku with a time window of 12 days. - 47 -
ECM 12ECM VLF Fig.9E Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in western and central Shikoku with a time window of 12 days. - 471 -
ECM 12ECM VLF Fig.A Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in Kii peninsula with a time window of 12 days. - 472 -
ECM 12ECM VLF Fig.B Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in Kii peninsula with a time window of 12 days. - 473 -
ECM 12ECM VLF Fig.C Spacetime distribution of tremors from the ECM catalog and low-frequency earthquakes from the JMA catalog in Kii peninsula with a time window of 12 days. - 474 -
11(a) 1 8 (b) Fig.11 (a) Spacetime distribution of starting points (green circle) and direction (arrow) of migrating tremors from the ECM catalog in southwest Japan from 1 to 8. The length of the solid line attached with arrow indicates the size of the tremor episode. (b) The percentage of the migration direction at each tremor segment. - 475 -
12(a)SSE SSE SSE SSESSE (b) 1 7 7 SSE (c) 1 7 7 SSE Fig.12 (a)(left) Relationship between the number of tremor source detection and moment of the slow slip event for each major episode. The blue line is the regression line estimated from the distribution. (Right) Frequency distribution of the number of the tremor source detection in each episode. The red bar indicates the episode associated with large-size slow slip event with slip parameters estimated by enough tilting data. Orange bard indicate the episodeassociated with small-size slow slip event with tilting step detected at only a few stations. (b) Spatial distribution of cumulative slip amount along the profile of A-B and C-D as shown in Fig.2. Yellow bars are cumulative slip amounts estimated from all of the tremor episodes. Green bars indicate the cumulative slip amounts from the tremor episode associated with the large-size slow slip events. (c) Time history of the cumulative slip amount at each point indicated in the insert map on the upper-left corner. Red lines indicate cumulative slip amounts estimated from all of the tremor episodes. Green dotted lines indicate the cumulative slip amounts from the tremor episode associated with the large-size slow slip events. Dashed lines are regression line estimated from each area. - 476 -