PRELIMINARY ANALYSIS OF THE EARTHQUAKE (MW 8.1) AND TSUNAMI OF APRIL
1, 2007, IN THE SOLOMON ISLANDS, SOUTHWESTERN PACIFIC OCEAN
Michael A. Fisher, Eric L. Geist, Ray Sliter, Florence L. Wong, Carol Reiss, and Dennis M. Mann
U.S. Geological Survey,
345 Middlefield Rd., MS 999, Menlo Park, California, USA
ABSTRACT
On April 1, 2007, a destructive earthquake (Mw 8.1) and tsunami struck the central Solomon
Islands arc in the southwestern Pacific Ocean. The earthquake had a thrust-fault focal mechanism and
occurred at shallow depth (between 15 km and 25 km) beneath the island arc. The combined effects of
the earthquake and tsunami caused dozens of fatalities and thousands remain without shelter. We
present a preliminary analysis of the Mw-8.1 earthquake and resulting tsunami. Multichannel seismic-
reflection data collected during 1984 show the geologic structure of the arc’s frontal prism within the
earthquake’s rupture zone. Modeling tsunami-wave propagation indicates that some of the islands are
so close to the earthquake epicenter that they were hard hit by tsunami waves as soon as 5 min. after
shaking began, allowing people scant time to react.
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1. INTRODUCTION
The M-8.1 earthquake in the Solomon Islands that occurred at 20:40 on April 1, 2007 (UTC),
struck along a complicated plate boundary in the southwestern Pacific Ocean (Figure 1). Earthquake
shaking and a tsunami caused as many as 52 fatalities and left thousands homeless (Reliefweb,
2007a). These figures remain unconfirmed because the affected area is impoverished and remote from
government resources. Clearly, however, this earthquake’s aftermath includes considerable human
suffering.
Figure 1. Index map of the part of the southwest Pacific Ocean that includes the Solomon Islands arc
and the epicenter of the 2007 Mw-8.1 subduction-zone earthquake. The crosshatched area shows the
rupture zone of the 2007 earthquake. The dotted outline shows the part of the island arc that has been
characterized by a reduced level of historical seismicity (Cooper and Taylor, 1987). The box shows
the area included in Figure 2a. Plate-convergence rates and directions are from Mann et al. (1998).
Science of Tsunami Hazards, Vol. 26, No. 1, page 4 (2007)
Figure 2a. Location of main shock (red circle) and aftershocks of the 2007 Mw-8.1 earthquake. Plate-
convergence rates and directions are from Mann et al. (1998). Black squares and numbers like “1975a
(7.6) ” give year, sequence and magnitude of doublet earthquakes that occurred in the rupture zone of
the 2007 earthquake. Figure area given in Figure 1. GI: Ghizo Island. KI: Kolombangara Island. NBT:
New Britain Trench. NGI: New Georgia Island. RI: Ranongga Island. SCT: San Cristobol Trench. SI:
Simbo Island. VI: Vangunu Island: VLI: Vela Lavella Island.
The Solomon Islands arc lies along the southwestern boundary of the Pacific plate, and the Mw-
8.1 earthquake was a subduction-zone thrust event. Several aspects of geography and geology make
this earthquake and tsunami unique. First, although young oceanic crust is being subducted eastward
at the New Britain Trench, the down going plate bends sharply downward and dips steeply (30˚ to
45˚) into the mantle, and the earthquake’s epicenter is located almost beneath the trench axis (Figure
2a). Second, in the past 30 years, numerous earthquake doublets have struck this island arc (e.g. Lay
and Kanamori, 1980), and the rupture zone of the 2007 earthquake includes the locations of two
doublets, having magnitudes of about M 7 (Figure 2a). To date (9/1/2007), however, the 2007 event
has produced aftershocks as large as Mb 6.6, but no second M-8 earthquake and tsunami have
occurred.
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Third, where the earthquake struck, complex bathymetric and tectonic elements, including an
active spreading ridge and transform fault, are being subducted. The effect of ridge subduction on
seismogenesis is evident from the fact that earthquake slip began southeast of where the spreading
ridge enters the subduction zone; slip was reduced directly over the ridge; and northwest of the ridge,
slip resumed with increased amplitude.
2. GEOLOGIC SETTING OF THE EPICENTRAL REGION
Since the middle Miocene, the Ontong Java Plateau (Figure 1) has been colliding with the trench
along the east side of the Solomon Islands arc (Kroenke, 1972; Mann and Taira, 2004; Phinney et al.,
1999). This collision caused eastward subduction of oceanic crust to commence along the west side of
the arc, forming an exemplar of subduction-polarity reversal (e.g. Karig and Mammerickx, 1972).
Earthquake hypocenters indicate that oceanic crust on both the east and the west sides of the island arc
is being subducted (e.g. Cooper and Taylor, 1985, 1987; Shinohara et al., 2003; Yoneshima et al.,
2005).
The 2007 Mw-8.1 earthquake occurred along the west side of the arc, where the New Britain and
San Cristobal Trenches mark the northeastward subduction of the oceanic plates on the west. This
crust includes the Solomon Sea plate to the north and the Australia plate to the south across the
Woodlark spreading ridge (Figure 1). Plate convergence between the Solomon Sea and Pacific plates,
is rapid, amounting to about 100 mm/yr (Bird, 2003; Tregoning et al., 1998).
The Woodlark spreading ridge extends discontinuously eastward across the Woodlark Basin to
where the ridge is being underthrust at the New Britain Trench, along the west side of the Solomon
Islands arc (Goodliffe, et al., 1999; Martinez, et al., 1999; Taylor, 1999; Taylor and Exon, 1987;
Weissel et al., 1982)(Figure 1). The spreading ridge figures prominently in this study because the
ridge enters the trench only about 50 km northwest of the epicenter for the 2007 earthquake (Figure
2b). North of the Woodlark spreading ridge, the New Britain Trench deepens northwestward, from
about 5 km near the ridge to as deep as 8 km west of Bougainville Island (Figure 1 and 2a). Across
the spreading ridge to the southeast, the San Cristobal trench is not well expressed bathymetrically, at
depths of 4 km to 5 km.
The Woodlark spreading ridge became active about 6 Ma ago (Taylor et al., 1999), and modeling
geodetic data indicates that the current half-spreading rate across the ridge increases progressively
eastward toward the New Britain Trench, where the half-rate may be as much as 40 mm/yr
(Tregoning et al., 1998).
This spreading ridge is segmented by several transform faults (e.g. Martinez et al., 1999; Taylor et
al., 1999). In particular, near the New Britain Trench the Simbo transform fault extends northward
from a spreading-ridge segment (Figure 2b) to obliquely underthrust the arc’s frontal prism. Swath-
bathymetric data indicate that the transform fault widens northeastward, which has been interpreted as
evidence for crustal spreading along this transform fault since about 80 ka (Martinez et al., 1999).
Ghizo Ridge, possibly an extinct segment of the spreading-ridge, is surmounted by seamounts and
extends southeastward along the axis of the San Cristobal Trench (Figure 2b). The epicenter of the
2007 earthquake is located just northeast of Ghizo Ridge and within a re-entrant in the forearc slope.
The Simbo bathymetric ridge, distinct from the transform fault, extends northward across the
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forearc slope and supports Simbo and Ranongga Islands (Figure 2b). These islands are near the trench
axis and were among the areas hardest hit by the 2007 tsunami. Simbo Ridge and its surmounting
islands apparently formed owing to subduction of the Woodlark spreading ridge. In this area,
spreading-ridge subduction mainly controls the location and intensity of near-trench volcanism (e.g.
Johnson et al., 1987; Taylor and Exon, 1987). Near the epicenter of the 2007 earthquake, volcanism is
restricted in occurrence to the area of New Georgia Island, east of where the spreading ridge is being
subducted. Near-trench volcanoes that formed Simbo Island actually lie west of the projected location
of the trench axis, and other volcanoes lie within just 30 km of this axis.
Figure 2b. The areas most severely affected by the tsunami include the near-trench islands of Simbo,
Ghizo and Ranongga and the southwest coast of Choiseul Island. Red circle shows the epicenter of the
2007 Mw-8.1 earthquake. The main fault-slip zones during the 2007 earthquake are separated by the
subducted Simbo transform fault. Figure area given in Figure 2a. Location of MCS section 401 in
Figures 3a and 3b is shown by the heavy part of the black line labeled “401”. The line of section
showing locally recorded hypocenters used in Figures 3b and 3c is shown by the black line labeled
“Y05”. Abbreviations as in Figure 2a except for: BI: Bougainville Island. CI: Choiseul Island. GR:
Ghizo ridge. REI: Rendova Island. TI: Tetepare Island. SLI: Shortland Island. SR: Simbo ridge. TRI:
Treasury Island.
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Another geologic consequence of ridge subduction is vertical tectonic motion of local forearc
areas. For example, Mann et al. (1998) and Taylor et al. (2005) described a high spatial variation in
uplift rates, near New Georgia Island, that the authors attribute to subduction of the irregular lower-
plate bathymetry. The 2007 epicenter is located within a re-entrant in the lower arc slope (Figure 2b).
Similar forearc re-entrants are scars caused by the subduction of high standing bathymetric features
(e.g. Fisher et al., 1991; Geist et al., 1993). How tectonic processes associated with ridge subduction
affected earthquake and tsunami generation are topics for further research.
3. THE 2007 EARTHQUAKE (MW 8.1)
Cooper and Taylor (1987) noted that epicenters of shallow (<70 km) and intermediate (70 km to
130 km) focal-depth earthquakes are uncommon in the central part of the island arc, as outlined in
Figure 1. This central area coincides with the locus of subduction of the Woodlark spreading center
(Cooper and Taylor, 1987). The epicenter for the 2007 earthquake occurred within the central zone of
reduced seismicity (Figure 1), thus filling at least the northwestern half of the seismic gap.
Global CMT Catalog data (CMT, 2007) indicate that the main shock was located at 7.96˚ S and
156.40˚ E at a depth of 23 km, and the nodal plane showing thrust-fault motion strikes 331˚ and dips
northeast at 38˚. Two other estimates of the attitude of the nodal plane yielded broadly similar values.
According to Yagi (2007), the strike is 300˚ and the dip 19˚, whereas Ji (2007) estimated the strike to
be 305˚ and dip 25˚. Fault rupture propagated northwestward from the epicenter at a mean velocity of
1.95 km/s (Yagi, 2007). The rupture zone of the 2007 earthquake extended at least 250 km along the
Solomon Islands arc. Within the two-month period following the main shock, as many as 10
aftershocks with Mb between 6 and 7 had occurred.
The Solomon Islands subduction zone is noted for producing earthquake doublets--two
earthquakes having similar magnitude that occur closely in space and time (Kagan and Jackson, 1999;
Lay and Kanamori, 1980; Schwartz, 1999; Xu and Schwartz, 1993). The mechanism causing
earthquake doublets remains controversial, although stress triggering of the second earthquake by the
first one in the doublet is likely to be a significant factor. Kagan and Jackson (1999) discuss the period
between doublet earthquakes.
The largest historic doublet to strike this island arc occurred 12 days apart during 1971 and
involved a pair of M-8.0 and -8.1 earthquakes north of Bougainville Island (Schwartz et al., 1989).
After the 2007 Mw-8.1 earthquake, despite deep concerns among disaster workers, a follow-on
earthquake and tsunami have not struck.
Most earthquake doublets in the Solomon Islands have occurred north of the 2007 epicenter, in the
vicinity of Bougainville Island and along the northwest-striking part of the New Britain Trench. Two
doublets during 1974 and 1975 were located within the northwestern part of the 2007 rupture zone
(Xu and Schwartz, 1993) (Figure 2a). The four events making up these doublets ranged in Mw from
7.3 to 7.6, and their focal mechanisms were compatible with underthrusting and subduction of the
western oceanic plate. Xu and Schwartz (1993) proposed that the 1974 and 1975 doublets originated
owing to the roughness of the oceanic plate that is being subducted because the Woodlark Rise enters
the New Britain Trench west of the epicenters.
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Subduction of high standing bathymetric features has demonstrably affected fault slip during the
2007 earthquake. According to two finite fault models (Ji, 2007; Yagi, 2007), fault rupture bridged
across the subducted part of the active Woodlark spreading ridge (Figure 2b). The finite fault models
differ in detail, but they agree to the extent that they show two main slip zones and a third small zone
near Vella Lavella Island. However, the slip zones by Yagi (2007) are shifted southwest from, and
indicate a slip magnitude nearly twice as great as, the slip zones and magnitude presented by Ji
(2007). Both models indicate that one of the two main slip zones surrounded the earthquake’s
epicenter and that the zones are separated by an area of slip deficit located where the Woodlark
spreading ridge and the Simbo transform fault are being subducted. In both models, the second or
northwestern main slip zone does not extend northwest of where the Woodlark Rise enters the trench
(Figure 2b), hence this bathymetric feature may have formed a barrier to earthquake rupture.
4. SEISMIC-REFLECTION SECTION THROUGH THE EARTHQUAKE RUPTURE ZONE
During 1984, the U.S. Geological Survey collected multichannel seismic-reflection (MCS) data in
the Solomon Islands arc (e.g. Bruns et al., 1989b). Seismic line 401 (Figs. 3a and 3b) from this survey
crosses the rupture zone of the 2007 earthquake (Figure 2b). Another version of this seismic section is
shown and interpreted in Bruns et al. (1989a). For this report, we reprocessed the seismic section,
migrating these data after stack and using sonobuoy-refraction velocities obtained over the lower
slope and Shortland basin (Cooper et al., 1986a,b, 1989) to produce a depth section without vertical
exaggeration (Figure 3b).
MCS section 401 reveals flat reflections from the interplate decollement that can be followed for
more than 40 km east of the trench (Figure 3a). These events separate discontinuous and weak
reflections from within the superjacent frontal prism of the island arc from more continuous
reflections from lower-plate rocks. The time and the depth-converted MCS sections (Figs. 3a and 3b)
reveal rocks under the decollement that dip consistently southeastward and terminate against the
abrupt seafloor rise that borders the New Britain Trench on the southeast. This rise is located along
the Simbo transform fault. Swath bathymetry shows that this transform fault strikes north, nearly
perpendicular to the seismic section, and the fault widens toward the New Britain Trench (Martinez et
al., 1998) (Figure 2b). Lower-plate rocks that dip southeast and abut the transform fault appear to fill
a half graben (Figs. 3a and 3b). This half graben may have resulted from the crustal spreading along
this transform fault that occurred since about 80 ka (Martinez et al., 1999), but the graben fill may be
too thick (~2 km) to have resulted solely from such a short period of extension. Alternatively, the
velocity used in the depth conversion is wrong and exaggerates the thickness.
To estimate the location of the interplate boundary northwest of where reflections from the
decollement end on MCS section 401, we plotted locally recorded hypocenters, instead of
teleseismically located ones, on the depth section (Figure 3b) and on a regional cross section (Figure
3c). The local hypocenters were determined from data obtained during a deployment of ocean-bottom
seismometers in 1998 (Yoneshima et al. 2005). Yoneshima et al. (2005) used these hypocenters to
show that the seismic front underlies the upper slope, consistently below the 1000 m isobath, and that
the down going plate dips ~30˚ northeast through the zone of highest seismic activity, which is deeper
than about 20 km. The water bottom multiple on MCS section 401 becomes a wide band of persistent
Science of Tsunami Hazards, Vol. 26, No. 1, page 9 (2007)
Figure 3a. Migrated time section of U.S. Geological Survey seismic line. Section location shown in
Figure 2b by the black line annotated “401”.
Science of Tsunami Hazards, Vol. 26, No. 1, page 10 (2007)
noise when migrated (Figure 3a), and it prevents us from making a direct connection between the
decollement indicated by reflections and the interplate boundary indicated by hypocenters.
Three seafloor discontinuities over the frontal prism may signify active thrust faults (Figs. 3a and
3b). The two discontinuities closer to the trench occur where reflections from within the prism are
poor, so the faults are speculative. However, reflections from near the shallowest seafloor
discontinuity yield better evidence for a thrust fault in that rocks at shallow depth on the fault’s
upslope side are more reflective and thicker than are rocks on the down slope side. Recent research
interest has focused on the role in tsunamigenesis played by splay thrust faults that deform a frontal
prism, especially in studies conducted off the Nankai Trough (e.g. Bangs et al., 2004; Kondo et al.,
2005; Park et al., 2000, 2002). Concerning the 2007 earthquake in the Solomon Islands, we currently
lack sufficient information to determine whether thrust faults interpreted from MCS section 401 (Figs.
3a and 3b) were active during the earthquake, but their potential role is a topic for future research.
The shallowest interpreted thrust fault coincides with an abrupt change in the critical taper of the
wedge (Figs. 3a and 3b). Over the lowermost slope, the wedge critical taper is 6˚ whereas at the
shallowest fault, the taper increases to 30˚, and the taper maintains this value eastward to beyond the
shelf break (Figure 3b). At other subduction zones, variations in the critical taper of the frontal prism
provide clues to how and where major earthquakes might nucleate along an interplate decollement
(Wang and Hu, 2006; Kimura et al., 2007). Furthermore, Kimura et al. (2007) discuss the Nankai
accretionary prism and link variations in critical wedge taper to specific structural styles within the
wedge and to mechanical properties along the decollement. In the analysis by Wang and Hu (2006)
the break in slope between a forearc basin and the outboard accretionary prism coincides with the
outward-directed change in frictional properties along the decollement from velocity-weakening to
velocity-strengthening. Hence, in this analysis the slope break is proposed to overlie the updip end of
the seismogenic zone.
These findings are difficult to apply straightforwardly to the case of the Solomon Islands arc near
MCS line 401 because the nearby subduction of the Woodlark spreading ridge, with its irregular
bathymetry and probable high heat flow, injects a strongly three-dimensional aspect into the analysis.
However, the half graben associated with the Simbo transform fault thins northeastward and appears
to die out altogether below the increase in critical taper (Figure 3a). Thus the critical-taper increase
from 6˚ to 30˚ may coincide with a change in frictional properties across the decollement: presumably
northwest of where the graben ends, lower-plate rocks just under the decollement are igneous oceanic
crust instead of sedimentary graben fill. This lithologic change might form the updip limit of the
seismogenic zone.
The seismic section shows what may be pinnacle reefs under shallow water near the shelf break
(Figure 3a). If they are reefs, then their flat upper surfaces indicate previous sea levels and the present
depth of the pinnacles indicates submergence and southeastward tilting of the shelf edge. This may be
evidence for subduction erosion of the upper plate by high standing bathymetric features thrust
beneath the island arc.
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5. THE TSUNAMI
According to news reports, the areas most severely affected by tsunami inundation include the
near-trench islands of Simbo, Ranongga, and especially Ghizo (e.g. Unosat, 2007) as well as the
southwest coast of Choiseul Island, which lies east of the Shortland Basin (Figure 2b). Reportedly, the
tsunami waves were between two and ten meters high and swept inland for almost half a kilometer
(Alertnet, 2007). Thirty-three of the 52 tsunami victims died on the most severely impacted island of
Ghizo, and 21 victims on this island were children (Alertnet, 2007; Reliefweb, 2007b). The
government of the Solomon Islands estimated that 30,000 people were affected by the earthquake and
tsunami. After the tsunami, many villages lacked suitable housing. Homes were swept away because
of the primitive construction techniques traditionally employed on the islands. Most houses have roofs
thatched with Sago palm leaves and supported by wooden poles. Many people remain in makeshift
hilltop camps, too frightened to return to coastal villages. Mental health issues among the affected
populace are of greater concern than is rebuilding, according to a team from the Asian Development
Bank, which is working with the government on an emergency assistance project (Disasternews,
2007). The humanitarian disaster attending the earthquake and tsunami led to a convention of many
government agencies to determine what lessons were learned that would aid recovery in case of a
future disaster (Reliefweb, 2007c).
The 2007 Solomon Islands seism does not appear to have been a "tsunami earthquake," defined as
one that produces a tsunami of far greater intensity than would be expected from the considering the
earthquake's magnitude alone (Kanamori, 1972; Kanamori and Kikuchi, 1993; Polet and Kanamori,
2000). The teleseismically determined location for the epicenter of the 2007 earthquake is close to the
axis of the San Cristobal trench, and a near-trench epicenter characterizes tsunami earthquakes.
However, observations concerning the 2007 earthquake do not accord with the other
characteristics of tsunami earthquakes listed in Polet and Kanamori (2000). Perhaps most significant
is the observed rupture velocity of 1.95 km/s (Yagi, 2007), which is higher than the low (as low as 1
km/s) rupture velocity typical of tsunami earthquakes (e.g., Ihmlé, 1996; López and Okal, 2006).
A more likely cause for the near-trench epicenter is the warm slab, including an active spreading
center, that is being subducted. A warm slab is thought to shift the seismogenic zone up dip along the
plate interface and to widen this zone, relative to the cold-slab case (Kirby, 2000; Peacock and
Hyndman, 1999; Peacock et al., 1999).
An exceptional tsunami could be caused by an earthquake rupturing inside a sedimentary wedge
made up of weak material, which conceptually could lead to enhanced seafloor motion (Fukao, 1979;
Okal, 1988). However, MCS data from the Solomon Island arc (Figure 3b) indicate that at least in the
northwest part of the rupture area of the 2007 earthquake, the frontal prism is narrow, measured
horizontally and perpendicular to the trench, and thin.
Although the 2007 tsunami had dire consequences for the Solomon Islands, the transoceanic
tsunami generated by this earthquake had only low amplitude (NGDC, 2007; NOAA, 2007). For
example, along the northeast coast of Australia, about 1600 km away from the epicenter, the wave
amplitude was about 0.1 m.
To create a preliminary numerical simulation of the April 2007 tsunami, we started with the fault
mechanism determined by the Global CMT Project (CMT 2007). The length of the fault that ruptured
Science of Tsunami Hazards, Vol. 26, No. 1, page 12 (2007)
was determined from the distribution of aftershocks and from seismic inversions (Ji, 2007; Yagi,
2007).The tsunami-source and -propagation model is based on the method in an earlier study (Geist
and Parsons, 2005) that investigated tsunamis from the November 2000 New Ireland earthquake
sequence. Animations showing the propagation of the 2007 Solomon Islands tsunami are available on
the internet (
http://soundwaves.usgs.gov/2007/04/
).
Figure 4. Numerical propagation model of the 2007 tsunami, based on the method in Geist and
Parsons (2005). The geographic area depicted here is the same as in Figure 2a. Colors show the
distribution of maximum calculated tsunami amplitude that occurred during the first 73 min. of
tsunami propagation. Red circle locates the epicenter of the Mw-8.1 earthquake. Dashed red and white
lines show trench axes. Red crosses show the locations of the marigrams in Figure 5. Red letters near
these crosses refer to specific marigrams. B: Bougainville. C1: Choiseul1. C2: Choiseul2. G1:Ghizo1.
G2: Ghizo2. Other abbreviations are as in Figures 2a and 2b.
Coarse-grid propagation modeling is useful for determining the open-ocean beaming pattern for
the tsunami. This modeling indicates that the highest offshore amplitudes occurred near the islands of
Simbo, Ghizo and Ranungga (Figure 4a), which accords with news reports. It is important to note,
Science of Tsunami Hazards, Vol. 26, No. 1, page 13 (2007)
however, that this modeling does not account for propagation near shore, where water is less than 100
m deep. Modeling shallow-water propagation requires high-resolution bathymetry (Titov and
Synolakis, 1998). We await field measurements of tsunami inundation to better constrain the tsunami
modeling. Also, tsunami modeling can be further refined using the specific slip distribution for this
earthquake derived from seismic-waveform analysis (Ji, 2007; Yagi, 2007).
Offshore synthetic marigrams derived from our tsunami modeling indicate that the first tsunami
wave arrived at hard-hit Ghizo Island within just 5 min. after the earthquake, and contrary to common
expectation, the ocean apparently did not withdraw prior to the tsunami's arrival (Figure 5A). The
brief period between the onset of the earthquake and the tsunami's arrival denied people time to
realize the imminent danger and react accordingly. In contrast, at islands like Choiseul that are farther
away from the trench significant wave heights arrived as much as 20 min. after the earthquake (Figure
5B). Local areas along the coast of Bougainville Island that face the New Britain Trench may have
experienced some inundation (Figure 5C).
Figure 5A. Synthetic offshore marigrams from the numerical tsunami model showing the calculated
wave height for at locations near Ghizo Island, which suffered the worst inundation, for 73 min. after
the earthquake. Marigram locations are shown in Figure 4. Water depths at Ghizo1 and Ghizo2 are
142 m and 104 m, respectively.
Figure 5B. Synthetic offshore marigrams near the west coast of Choiseul Island. Marigram locations
are shown in Figure 4. Water depths at Choiseul1 and Choiseul2 are 114 m and 114 m, respectively.
Figure 5C. Synthetic offshore marigrams near the west and southwest coasts of Bougainville Island.
Marigram locations are shown in Figure 4. Water depths at Bougainville and Alu are 155m and 134
m, respectively.
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6. CONCLUSION
The Mw-8.1 earthquake and tsunami that struck the Solomon Islands on April 1, 2007, had
substantial long-term impact on local population centers. This earthquake-driven tsunami revealed
particular challenges for government agencies in trying to warn local population centers, because only
a short time passed between the onset of shaking and arrival of tsunami waves.
The geologic complexity of the plate boundary where the 2007 earthquake struck provides fertile
ground for future research. Reprocessing MCS data from other parts of the earthquake’s rupture zone
will promote better understanding about the origin of this and other tsunamis that originate in
subduction zones. Other research topics include the influence of ridge subduction on seismogenesis
and the role of splay thrust faults deforming the frontal prism in the generation of tsunamis.
Science of Tsunami Hazards, Vol. 26, No. 1, page 15 (2007)
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