The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast.
The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.
Key words: Harvard CMT catalogue, Sumatra–Andaman seismic region, seismic quiescence, earthquake doublets and multiplets, seismic moment release.
S.J. GIBOWICZ and W. DĘBSKI 344
1. INTRODUCTION
The Sumatra earthquake of 26 December 2004 with moment magnitude Mw = 9.3 (Tsai et al. 2005) was the largest seismic event in the world in more than 40 years. Such giant events occur where large oceanic plates underthrust continental margins. The Sumatra earthquake ruptured about 1300 km of a curved plate boundary between the Indo-Australian plate and the southeastern portion of the Eurasian plate, extending from Northwestern Sumatra to the Andaman Islands. The second great earthquake of 28 March 2005 (Mw = 8.6) ruptured an adjacent 300 km long portion of the plate boundary along Northern Sumatra (e.g., Lay et al. 2005).
Like other great earthquakes, the Sumatra event of 2004 ruptured mostly unilaterally. According to the inferred rupture process, the rupture area is divided into three segments (Ammon et al. 2005, Lay et al. 2005). The rupture started at the southeastern edge of the Sumatra segment, with the initial 50 s of rupture charac-terized by low energy release and slow rupture velocity. The rupture front then expanded to the north-northwest, extending up to 1300 km. The next 180 s were characterized by a large rapid slip up to 20 m. The Sumatra segment was the source of the main tsunami excitation. From 230 to 350 s the Nicobar segment ruptured, with a moderate slip of about 5 m. Then, from 350 to 600 s, the Andaman segment ruptured and was characterized by a small rapid slip of less than 2 m. The multiple centroid-moment-tensor (CMT) analysis of Tsai et al. (2005) shows five CMTs in the final model; two of them corresponding to the Sumatra segment and the last two to the Andaman segment.
The 2004 great Sumatra event, one of the most important earthquakes of the century, is extensively studied using modern observations and analysis methods. Different aspects of the rupture process, its extent, speed and duration are studied by a variety of seismic methods (Ammon et al. 2005, Lay et al. 2005, Ni et al. 2005, Stein and Okal 2005, Tsai et al. 2005), including free oscillations of the Earth (Park et al. 2005, Stein and Okal 2005) and teleseismic approach (Ishii et al. 2005, Krüger and Ohrnberger 2005). The relationship between the source and subduction zone structure, different behaviour of the source corresponding to changes in the physical properties of the subducted slab along the Sumatra-Andaman arc, is revealed by seismic tomography (Kennett and Cummins 2005). Additional insight into the source and constraints on the rupture are provided by modern GPS observations (Banerjee et al. 2005, Catherine et al. 2005, Vigny et al. 2005).
In this study, an analysis of seismicity patterns before the 2004 earthquake, between the 2004 and 2005 events, and after the 2005 earthquake is undertaken. The analysis is based on the Harvard CMT catalogue (Dziewonski and Woodhouse 1983, Dziewonski et al. 1981) that contains the CMT solutions for all the earthquakes from 1977 to the present day, with moment magnitude in general greater than about 5. Thus, the analysis is limited to some extent by the size of events. These medium and large earthquakes are, on the other hand, the best elaborated events that form the most uniform set of data, and are responsible for the largest release of seismic moment in the studied area.
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 345
2. DATA
The studied rupture area of the two great earthquakes of 26 December 2004 and 28 March 2005 extends from 3°S to 14°N of latitude and from 91°E to 102°E of longitude and is slightly modified in comparison with that of Lay et al. (2005) to include seismicity to the southeast from the 2005 event. The time interval from 1 January 1977 to 30 November 2005, almost 29 years of duration, was searched for the earthquakes from the studied area. Only shallow events, not deeper than 60 km, were accepted. Before the 2004 great earthquake, 63 events occurred at a depth greater than 60 km and none after its occurrence.
Altogether, 481 earthquakes that fulfill the above criteria are listed in the catalogue. The first listed event occurred on 8 March 1977. The smallest earthquake has moment magnitude 4.8, but the threshold value of magnitude above which the data are complete is about 5.2, and the corresponding number of events is 402.
Fig. 1. Surface distribution of the Harvard CMT locations of 230 earthquakes that occurred be-tween 1 January 1977 and the great earthquake of 26 December 2004 within the studied region. The size of symbols is propor-tional to the earthquake magni-tude. The two great earthquakes of 2004 and 2005 are marked by stars.
S.J. GIBOWICZ and W. DĘBSKI 346
3. SPACE DISTRIBUTION AND FREQUENCY–MAGNITUDE RELATIONS
There are 230 shallow earthquakes listed in the Harvard catalogue, that occurred before the great earthquake of 2004. Their surface location in centroid coordinates is shown in Fig. 1. The earthquake of 26 December 2004, located in centroid coordinates at 3.09°N of latitude and 94.26°E of longitude, and the event of 28 March 2005, located at 1.64°N of latitude and 96.98°E of longitude, are marked by stars. The surface distribution of these earthquakes is not uniform and the source area of the 2004 event appears as an area of distinct quiescence with a radius of about 100 km, where even medium-size earthquakes have not occurred during the last 29 years. From the NEIC earthquake catalogue, Dasgupta et al. (2005) found that during one month preceding the earthquake of 26 December 2004 there was also a clear seismic quiescence in the area on a much lower level of earthquake magnitude.
Fig. 2. Surface distribution of the Harvard CMT locations of 186 earthquakes that occurred be-tween the 26 December 2004 and 28 March 2005 great events, marked by stars.
There are 186 earthquakes that occurred between the two great events of 2004 and 2005. Their surface distribution in centroid coordinates is shown in Fig. 2.
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 347
Virtually all of them, but one, are located to the northwest from the location of the great earthquake of 2005, forming three distinct clusters of aftershocks in Northern Sumatra, around the Nicobars and the Andaman Islands. Little of aftershock activity towards the south appears also on a lower level of earthquake magnitude until the occurrence of the 28 March 2005 earthquake (Ammon et al. 2005). The most notable aftershock feature is a vigorous swarm of events in the Andaman Sea back-arc basin that occurred at the end of January 2005 (Lay et al. 2005).
Because the great earthquake of 2004 ruptured only a segment of the subduction zone, it increased stress on adjacent segments, further south on the Sumatran trench (McCloskey et al. 2005), and a first consequence of that was the earthquake of 28 March 2005 (Vigny et al. 2005). It was followed by 63 events listed in the Harvard catalogue, mostly its aftershocks, that occurred by the end of November 2005. Their surface distribution is shown in Fig. 3.
Fig. 3. Surface distribution of the Harvard CMT locations of 63 earthquakes that occurred by the end of November 2005 after the great event of 28 March 2005. The two great earthquakes are marked by stars.
Consecutive distribution of moment magnitude of all selected 481 earthquakes is shown in Fig. 4. The number of aftershocks with moment magnitude 5 or greater
S.J. GIBOWICZ and W. DĘBSKI 348
following both the great earthquakes is surprisingly small for such gigantic events. Furthermore, the largest aftershocks in both cases are too small to follow Båth’s (1965) law, describing the average magnitude difference between the main shock and its largest aftershock. The largest aftershock of the 2004 event occurred almost immediately, 3 hours and 20 minutes after the main shock, had magnitude 7.2, and the magnitude difference was 2.1. The largest aftershock of the 2005 event occurred on 19 May, over 51 days after the main shock, had magnitude 6.9, and the magnitude difference was 1.7. The largest earthquake of magnitude 7.3 (Fig. 4) following the 2005 event occurred on 24 July in the region of Nicobar Islands and could not be considered as an aftershock.
Fig. 4. Sequential distribution of the Harvard CMT moment magnitude of 481 earthquakes that occurred between 1 January 1977 and 30 November 2005.
The cumulative frequency-magnitude relations are estimated separately for the three data sets related to seismicity before and after the two great earthquakes and are shown in Fig. 5. For earthquakes that occurred before the 2004 event, the threshold value of magnitude is 5.15 and the corresponding number of events is 217. The largest event occurred on 2 November 2002 and had moment magnitude 7.3. The slope coefficient b is practically equal to one, the most often observed and postulated value (e.g., Felzer et al. 2004). Nuannin et al. (2005) found, on the other hand, considerable space and time variations of b values calculated from 624 earthquakes that occurred between 1 January 2000 and 25 December 2004, and considered them as an expression of stress accumulation.
For earthquakes that occurred between the two great events, the magnitude threshold is 5.3 and for those that occurred after the great event of 2005 it is 5.4, and
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 349
Fig. 5. Cumulative frequency-magnitude relations for earthquakes that occurred before the great event of 2004 (open circles), between the two great events (stars) and after the great event of 2005 (crosses). For the sake of clarity, the upper curve (1) and middle curve (2) are moved up by two and one decades, respectively. The total number of events is shown on the left-hand side of each curve. Their approximations are marked by straight lines and the corresponding values of the slope coefficient b are also given.
the corresponding number of events is 147 and 55, respectively. The value of coefficient b from earthquakes that occurred between the two great earthquakes is rather high, about 1.3. This implies that the proportion of smaller events to larger events is higher than that observed before the 2004 event. The value of coefficient b, on the other hand, describing the relation for earthquakes that occurred after the 2005 event is about 0.9, close to the most often observed value of one.
4. EARTHQUAKE DOUBLETS AND MULTIPLETS
Earthquake interaction is a fundamental feature of seismicity, expressed as earthquake sequences and clustering in space and time. The occurrence of one earthquake increases the probability of the occurrence of a second earthquake, leading to seismic doublets and multiplets. Recently Felzer et al. (2004) demonstrated that the statistics of earthquake data in several catalogues are consistent with a single triggering mechanism responsible for the occurrence of aftershocks, foreshocks, and multiplets.
S.J. GIBOWICZ and W. DĘBSKI 350
There is no clear definition of an earthquake doublet or multiplet. In search for earthquake multiplets in the studied region we follow the criteria used before (Gibowicz and Lasocki 2005). We specify a doublet as a pair of earthquakes with a magnitude difference of no more than 0.2 unit, whose centroids are separated by no more than 40 km for events with magnitude from 4.8 to 5.4, 60 km for events with magnitude from 5.5 to 5.9, and 90 km for events with magnitude equal or greater than 6.0, and whose difference in time of occurrence is not longer than 200, 300 and 450 days, respectively.
The doublets and multiplets were selected separately within three time intervals containing earthquakes that occurred before the great event of 2004, between the two great events, and after the great event of 2005. The first time interval is equal to 28 years and 20 days, the second interval corresponds to 93 days, and the third interval is 241 days long. The accepted time criterion therefore is exact for the first interval only and is smaller for the other two, but there are a few pairs with the time separation exceeding 100 days (Fig. 6).
Fig. 6. The distance against the time interval between two events forming a pair for earthquakes that occurred before the great event of 2004 (open circles), between the two great events (stars) and after the great event of 2005 (crosses). Two dashed lines indicate the distance of 20 km and the time interval of 5 days, respectively. The total number N of pairs is indicated.
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 351
In the first time interval we have 21 doublets and 6 triplets, forming 33 pairs of earthquakes out of 60 events associated with doublets and multiplets (26% of all events), whose centroids are located at a distance ranging from 3 to 56 km and whose time separation ranges from 0.00067 to 425 days (exceeding 100 days in 5 pairs). In the second time interval we have 30 doublets, 6 triplets, 5 quadruplets and 1 quintuplet, forming 61 pairs out of 103 associated events (55% of all events), with the distance separation ranging from 1 to 48 km and the time difference ranging from 0.016 to 55 days. In the third interval we have 9 doublets, 2 triplets and 1 quadruplet, forming 16 pairs out of 28 associated events (44% of all events), with the distance interval ranging from 4 to 89 km and the time separation ranging from 0.072 to 205 days (exceeding 100 days in 3 pairs). Thus, about a quarter of earthquakes that occurred before the great event of 2004 and a half of those that occurred after the two great events are associated with doublets and multiplets. Some of these pairs might be connected with aftershocks, though their number is surprisingly small (Figs. 9 and 10).
Fig. 7. Surface distribution of the Harvard CMT locations of 191 earth-quakes associated with doublets and multiplets, that occurred before the great event of 2004 marked by train-gles, between the two great events marked by rhombs and after the great event of 2005 marked by circles. The symbols are proportional to the earth-quake magnitude. The two great earth-quakes are marked by stars.
The distance against the time separation between two events forming a pair is shown on a logarithmic scale in Fig. 6. The distance of 20 km and the time difference of 5 days are marked to underline the pairs with the shortest distance and time
S.J. GIBOWICZ and W. DĘBSKI 352
separation. The distance of 20 km is directly related to the location accuracy of earthquakes, and about two thirds of all pairs have the time separation not greater than 5 days. Neither the time interval, nor the distance appear to be dependent on magnitude of the events forming the pairs. Surface distribution of all the earthquakes associated with doublets and multiplets within the three time intervals is shown in Fig. 7.
The 3D angle of rotation (Kagan 1991, 1992) between focal mechanisms of two earthquakes, that would transform the focal mechanism of one event into that of another event forming a pair, is less than 30o in about 40% of all cases, and thus both events in these pairs have similar focal mechanism (Kagan and Jackson 1999). The focal mechanism of all earthquakes that occurred before the great event of 2004 and those between the two great events of 2004 and 2005 is surprisingly similar and almost equally divided between the strike slip, normal and reverse type of faulting. The earthquakes that occurred after the great event of 2005, on the other hand, are dominated by reverse faulting in over 80% cases.
The degree of fault rupture overlap η in a pair is the sum of the respective rupture lengths of the two earthquakes forming a pair divided by the double distance between their centroids (Kagan and Jackson, 1999). The rupture lengths were estimated using relations given by Wells and Coppersmith (1994). The values of η larger than 1.0 imply that the rupture zones of both earthquakes overlap. Before the occurrence of the great earthquake of 2004 we have 2 pairs (6% of all pairs) with the η values in excess of 1.0 and 5 pairs (15% of all pairs) with the η not smaller than 0.5. After the occurrence of the great earthquake of 2004, by the end of November 2005, we have 12 pairs (16% of all pairs) with the η not smaller than 1.0 and 28 pairs (36% of all pairs) with the η greater or equal to 0.5. Thus, the fault rupture overlap in our pairs of earthquakes appears to be complete about three times more often after the occurrence of the great events than before the occurrence of the first 2004 great earthquake.
5. RELEASE OF SEISMIC MOMENT IN TIME AND SPACE
The release of seismic moment as a function of time for earthquakes that occurred before the great event of 2004 is shown in Fig. 8. The cumulative seismic moment increased rather regularly with time, with two distinct jumps of its value corresponding to the occurrence of two earthquakes in Northern Sumatra with magnitude greater than 7 in November 1984 and in November 2002, some twenty years and two years before the occurrence of the great earthquake, but there are no visible changes immediately before its occurrence. The sum of seismic moment released during 28 years before the 2004 earthquake is equal to 3.61E20 N·m that would correspond to a single earthquake of moment magnitude 7.6, and forms only a small part, 0.3%, of the seismic moment released by the great event.
The cumulative seismic moment as a function of time for earthquakes that occurred between the two great events is shown in Fig. 9. It increased rapidly during the first ten-fifteen days, displaying mostly the release of immediate aftershocks, then
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 353
Fig. 8. Cumulative seismic moment as a function of time for 230 earthquakes that occurred before the great event of 2004.
Fig. 9. Cumulative seismic moment as a function of time for 186 earthquakes that occurred between the 2004 and 2005 great events.
S.J. GIBOWICZ and W. DĘBSKI 354
it flattened out and increased slowly with time. Thus, the largest aftershocks were generated during surprisingly short interval of time. The only rapid increase of seismic moment later on is observed about a month before the major event of 28 March 2005, related to the occurrence of an earthquake of magnitude 6.7 on 26 February 2005. The sum of seismic moment released between the two earthquakes of 2004 and 2005 is equal to 1.67×1020 N·m that is only about twice smaller than that released during 28 years before the 2004 great earthquake and would correspond to a single event of magnitude 7.4.
The release of seismic moment during earthquakes that occurred after the 2005 major event, presented in Fig. 10, shows firstly a quiet increase during some 115 days, corresponding to the release of aftershocks, and then a sudden jump related to the occurrence of an earthquake with moment magnitude 7.3 in the region of Nicobar Islands. After that, very small activity is in progress until the end of our observations.
Fig. 10. Cumulative seismic moment as a function of time for 63 earthquakes that occurred by the end of November 2005 after the great event of 2005.
To investigate the spatial distribution of seismic moment release, the studied region was divided into small squares with an equal area of 0.5×0.5° and the seismic moment of earthquakes within these squares was summed up. The spatial distribution before the great earthquake of 2004, shown in Fig. 11, indicates that the largest release of seismic moment in the region occurred to the southeast of the CMT location of the 2004 great event, around the rupture area of the major earthquake of 2005. This pattern correlates to some extent with that of stress concentration indicated by low
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 355
values of coefficient b calculated for the period from 1 January 2000 to 25 December 2004 by Nuannin et al. (2005). The elongated area of large seismic moment release in the SW-NE direction, nearest to the CMT location of the 2004 event, coincides with a transverse hinge lithospheric fault inferred by Dasgupta et al. (2003), who suggested the presence of several transverse faults in the studied region, dissecting the subducting lithosphere into segments that undergo deformation.
Fig. 11. Spatial distribution of seismic moment summed up within 118 equal area squares of 0.5o×0.5o containing earthquakes that occurred before the great event of 2004. The two great events are marked by stars. The shading of squares is proportional to the corresponding sums of seismic moment ranging from 3.5×1016 to 9.4×1019 N⋅m.
It appears therefore that the spatial distribution of the release of seismic moment between the two great earthquakes of 2004 and 2005, shown in Fig. 12, is affected not only by the occurrence of aftershocks of the 2004 event but also by the large release of seismic moment in the south of the region before the occurrence of the 2004 event. The largest release is now observed in the vicinity of the 2004 event and in the area of
S.J. GIBOWICZ and W. DĘBSKI 356
Nicobar Islands, further up to the north. No earthquakes are practically present in the southern part of the studied region.
Fig. 12. Spatial distribution of seismic moment summed up within 77 equal area squares of 0.5o×0.5o
containing earthquakes that occur-red between the 2004 and 2005 great events marked by stars. The shading of squares is proportional to the corresponding sums of seismic moment ranging from 2.0×1016 to 7.3×1019 N⋅m.
The spatial distribution of seismic moment after the occurrence of the great earthquake of 2005 follows, not surprisingly, the reverse trend (Fig. 13). The release of seismic moment is the largest in the vicinity of the 2005 event and further down to the southeast from its CMT location.
6. DISCUSSION AND CONCLUSIONS
Earthquakes that occurred in the studied region between 1977 and the great earthquake of 26 December 2004 were irregularly distributed in space and the source area of the great event appears as an area of seismic quiescence, where no earthquakes with
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 357
Fig. 13. Spatial distribution of seismic moment summed up within 35 equal area squares of 0.5o×0.5o containing earthquakes that occurred by the end of November 2005 after the great event of 2005. The two great events are marked by stars. The shading of squares is proportional to the corresponding sums of seismic moment ranging from 6.1×1016 to 8.8×1019 N⋅m.
magnitude greater than about 5 occurred in 28 years. There are 60 earthquakes associated with doublets and multiplets (26% of all events), forming 33 pairs; 2 of them (6% of all pairs) with complete fault rupture overlap. The cumulative seismic moment from earthquakes preceding the great event increased regularly with time, with two sudden jumps of its value about twenty years and two years before the occurrence of the great event. The largest amount of seismic moment was released to the southeast of the CMT location of the 2004 event, around the rupture area of the great earthquake of 28 March 2005. Furthermore, the area of large seismic moment release elongated in the SW-NE direction, nearest to the CMT location of the 2004 event, coincides with a transverse hinge lithospheric fault inferred by Dasgupta et al. (2003). This transverse fault seems to divide the studied region into the area of high stress accumulation (low seismic moment release) in the north and the area of low stress accumulation (high seismic moment release) in the south.
S.J. GIBOWICZ and W. DĘBSKI 358
Virtually all earthquakes, but one, with magnitude greater than about 5 that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005 are located to the northwest from the postulated transverse fault in Northern Sumatra and from the CMT location of the great earthquake of 2005. Their frequency–magnitude relation is described by a high value of the coefficient b, equal to 1.3, implying the domination of smaller events over larger events in our set of observations. There are 103 earthquakes (55% of all events) forming 61 pairs; 9 of them (15% of all pairs) with complete fault rupture overlap. The cumulative seismic moment increased rapidly during the first ten-fifteen days, corresponding to the release of immediate aftershocks, then it flattened out and increased slowly with time. The largest aftershocks therefore were generated during surprisingly short time. A distinct increase of seismic moment is observed a month before the occurrence of the 2005 great earthquake. The largest release of seismic moment is observed in the vicinity of the 2004 event and in the area of Nicobar Islands.
Earthquakes that occurred between 28 March and 30 November 2005 are mostly located around the rupture area of the 2005 great event and a few of them are located further north, up to the Nicobar Islands. In the source area of the 2004 event there appears again the area of quiescence, that is also apparent around the postulated transverse lithospheric fault. There are 28 events (44% of all events) forming 16 pairs; 3 of them (19% of all pairs) with complete fault rupture overlap. The cumulative seismic moment increased quietly during the first 115 days and then a sudden jump of its value appeared, followed by very small activity till the end of our observations. The seismic moment was mostly released in the vicinity of the 2005 great event and further down to the south, following the opposite trend than that observed between the occurrence of the two great earthquakes.
Acknowledgemen t s . All figures, except Figs. 5 and 6, are created using the GMT software (Wessel and Smith 1995).
R e f e r e n c e s
Ammon, C.J., C. Ji, H.-K. Thio, D. Robinson, S. Ni, V. Hjorleifsdottir, H. Kanamori, T. Lay, S. Das, D. Helmberger, G. Ichinose, J. Polet, and D. Wald, 2005, Rupture process of the 2004 Sumatra-Andaman earthquake, Science 308, 1133-1139.
Banerjee, P., F. F. Pollitz, and R. Bürgmann, 2005, The size and duration of the Sumatra-Andaman earthquake from far-field static offsets, Science 308, 1769-1772.
Båth, M., 1965, Lateral inhomogeneities in the upper mantle, Tectonophysics 2, 483-514. Catherine, J. K., V. K. Gahalaut, and V. K. Sahu, 2005, Constraints on rupture of the
December 26, 2004, Sumatra earthquake from far-field GPS observations, Earth Planet. Sci. Lett. 237, 673-679.
Dasgupta, S., M. Mukhopadhyay, A. Bhattacharya and T. K. Jana, 2003, The geometry of the Burmese-Andaman subducting lithosphere, J. Seism. 7, 155-174.
SEISMICITY BEFORE AND AFTER TWO GREAT SUMATRA EARTHQUAKES 359
Dasgupta S., B. Mukhopadhyay and A. Acharyya, 2005, Aftershock propagation characteris-tics during the first three hours following the 26 December 2004 Sumatra–Andaman earthquake, Gondwana Res. 8, 585-588.
Dziewonski, A. M., and J.H. Woodhouse, 1983, An experiment in systematic study of global seismicity: Centroid-moment tensor solutions for 201 moderate and large earthquakes of 1981, J. Geophys. Res. 88, 3247-3271.
Dziewonski, A. M., T.-A. Chou, and J.H. Woodhouse, 1981, Determination of earthquake source parameters from waveform data for studies of global and regional seismicity, J. Geophys. Res. 86, 2825-2852.
Felzer, K.R., R.E. Abercrombie and G. Ekström, 2004, A common origin for aftershocks, foreshocks, and multiplets, Bull. Seism. Soc. Am. 94, 88-98.
Gibowicz, S.J., and S. Lasocki, 2005, Earthquake doublets and multiplets in the Fiji-Tonga-Kermadec region, Acta Geophys. Pol. 53, 239-274.
Ishii, M., P.M. Shearer, H. Houston and J. E. Vidale, 2005, Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-Net array, Nature 435, 933-936.
Kagan, Y.Y., 1991, 3-D rotation of double-couple earthquake sources, Geophys. J. Int. 106, 709-716.
Kagan, Y.Y., 1992, Correlations of earthquake focal mechanisms, Geophys. J. Int. 110, 305-320.
Kagan, Y.Y., and D.D. Jackson, 1999, Worldwide doublets of large earthquakes, Bull. Seism. Soc. Am. 89, 1147-1155.
Kennett, B.L.N., and P.R. Cummins, 2005, The relationship of the seismic source and subduction zone structure for the 2004 December 26 Sumatra-Andaman earthquake, Earth Planet. Sci. Lett. 239, 1-8.
Krüger, F., and M. Ohrnberger, 2005, Tracking the rupture of the Mw = 9.3 Sumatra earth-quake over 1,150 km at teleseismic distance, Nature 435, 937-939.
Lay, T., H. Kanamori, C.J. Ammon, M. Nettles, S.N. Ward, R.C. Aster, S.L. Beck, S.L. Bilek, M.R. Brudzinski, R. Butler, H.R. DeShon, G. Ekström, K. Satake and S. Sipkin, 2005, The great Sumatra–Andaman earthquake of 26 December 2004, Science 308, 1127-1133.
McCloskey, J., S.S. Nalbant and S. Steacy, 2005, Earthquake risk from co-seismic stress, Nature 434, 291.
Ni, S., H. Kanamori and D. Helmberger, 2005, Energy radiation from the Sumatra earthquake, Nature 434, 582.
Nuannin, P., O. Kulhanek and L. Persson, 2005, Spatial and temporal b value anomalies preceding the devastating off coast of NW Sumatra earthquake of December 26, 2004, Geophys. Res. Lett. 32, L11307, doi: 10.1029/2005GL022679.
Park, J., T.-R.A. Song, J. Tromp, E. Okal, S. Stein, G. Roult, E. Clevede, G. Laske, H. Kanamori, P. Davis, J. Berger, C. Braitenberg, M. Van Camp, X. Lei, H. Sun, H. Xu and S. Rosat, 2005, Earth’s free oscillations excited by the 26 December 2004 Sumatra-Andaman earthquake, Science 308, 1139-1144.
Stein, S., and E.A. Okal, 2005, Speed and size of the Sumatra earthquake, Nature 434, 581-582.
S.J. GIBOWICZ and W. DĘBSKI 360
Tsai, V.C., M. Nettles, G. Ekström and A.M. Dziewonski, 2005, Multiple CMT source analysis of the 2004 Sumatra earthquake, Geophys. Res. Lett. 32, 17304,doi: 10.1029/2005GL023813.
Vigny, C., W.J.F. Simons, S. Abu, R. Bamphenyu, C. Satirapod, N. Choosakul, C. Subarya, A. Socquet, K. Omar, H.Z. Abidin and B.A.C. Ambrosius, 2005, Insight into the 2004 Sumatra–Andaman earthquake from GPS measurements in southeast Asia, Nature 436, 201-206.
Wells, D.L., and K.J. Coppersmith, 1994, New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement, Bull. Seism. Soc. Am. 84, 974-1002.
Wessel, P., and W.H.F. Smith, 1995, New version of the Generic Mapping Tools released, EOS Trans. AGU 76, 329.
