Tsunami Source of the 2010 Mentawai, Indonesia Earthquake Inferred from Tsunami Field Survey and Waveform Modeling
- 5k Downloads
- 49 Citations
Abstract
The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 1021 Nm, which corresponded to Mw 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.
Keywords
Tsunami earthquake Mentawai earthquake Indonesia Indian ocean1 Introduction
Tectonics and previous earthquakes off the west Sumatra Island
On 25 October 2010, a large earthquake (M 7.7) occurred off the west coast of the Mentawai Islands. According to the USGS, the origin time was 14:42:22 UTC (or 21:42:22 local time, or WIB), the epicenter was 3.484°S, 100.114°E, and the depth was 20.6 km. Badan Meteorologi Klimatologi Dan Geofisika (BMKG) of Indonesia estimated the magnitude as 7.2 and issued a tsunami warning within 5 min of the earthquake (Badan Meteorologi Klimatologi Dan Geofisika 2010). Without receiving information of tsunami damage, they cleared the tsunami warning 52 min after the earthquake.
Source time functions, or seismic moment release rates, of the 2009 Padang (M 7.6) and 2010 Mentawai (M 7.7) earthquakes, estimated by finite fault modeling of the USGS
In this article, we first report our field survey results (Sect. 2). Sedimentary analysis of tsunami deposits was also carried out in our survey, but will be separately reported by Putra et al. (2012). Our Indonesian-Japanese team conducted the field survey 2 weeks after the earthquake when the sea conditions were very rough. This survey was followed by those of an Indonesian–German team (Kerpen et al., 2011) and an Indonesian–Singaporean–US team (Hill et al., 2012). We also present instrumentally recorded tsunami waveforms (Sect. 3.1) and our modeling results of waveform inversion (Sects. 3.2 and 3.3). Lay et al. (2011) modeled the tsunami waveform recorded at a DART station, ~1,600 km away from the epicenter, but other tsunami waveforms recorded at nearer stations have not been modeled. We further report detailed tsunami computation results from the tsunami source model (Sects. 3.4 and 3.5).
2 Tsunami Survey and Coastal Tsunami Heights
2.1 Method
a Definitions of inundation distance, run-up height, tsunami (inundation) height, and flow depth. b Predicted tide level change at Sikakap during the survey period
Tsunami heights measured by the field survey
Site | Latitude | Longitude | Tsunami height | Run-up height | Flow depth | Inundation distance | Date | Local time | Mark | |
---|---|---|---|---|---|---|---|---|---|---|
(m) | (m) | (m) | (m) | (hours) | ||||||
1 | Asahan | 03°03′18″S | 100°14′13″E | 6.4 | 6.0 | 41 | 06-Nov-2010 | 1424 | BB | |
2 | Asahan | 03°03′18″S | 100°14′13″E | 9.3 | 38 | 06-Nov-2010 | 1424 | BB | ||
3 | Asahan | 03°03′18″S | 100°14′13″E | 6.6 | 6.6 | 9 | 06-Nov-2010 | 1424 | BB | |
4 | Purorougat | 03°02′12″S | 100°13′55″E | 5.5 | 06-Nov-2010 | BB | ||||
5 | Lopon Lakau | 03°12′39″S | 100°21′02″E | 2.5 | 23 | 07-Nov-2010 | 0840 | BB | ||
6 | Maonai | 03°11′31″S | 100°20′41″E | 6.8 | 3.9 | 259 | 07-Nov-2010 | 1130 | BB | |
7 | Maonai | 03°11′33″S | 100°20′38″E | 6.9 | 3.8 | 182 | 07-Nov-2010 | 1130 | RD | |
8 | Maonai | 03°11′34″S | 100°20′39″E | 6.7 | 3.6 | 181 | 07-Nov-2010 | 1130 | BB | |
9 | Maonai | 03°11′36″S | 100°20′39″E | 6.7 | 3.5 | 206 | 07-Nov-2010 | 1130 | BB | |
10 | Maonai | 03°11′30″S | 100°20′42″E | 7.3 | 0.0 | 315 | 07-Nov-2010 | 1130 | ER, EW | |
11 | Sabeu Gunggung | 02°48′59″S | 100°03′29″E | 5.0 | 3.9 | 31 | 08-Nov-2010 | 0900 | BB | |
12 | Sabeu Gunggung | 02°48′57″S | 100°03′28″E | 5.8 | 3.9 | 75 | 08-Nov-2010 | 0900 | BB | |
13 | Sabeu Gunggung | 02°48′57″S | 100°03′28″E | 7.0 | 4.8 | 75 | 08-Nov-2010 | 0900 | BB | |
14 | Sabeu Gunggung | 02°48′52″S | 100°03′28″E | 4.3 | 4.3 | 217 | 08-Nov-2010 | 0900 | BB | |
15 | Muntei | 02°49′46″S | 100°05′46″E | 5.7 | 3.8 | 287 | 08-Nov-2010 | 1411 | BB | |
16 | Muntei | 02°49′46″S | 100°05′46″E | 4.6 | 1.6 | 241 | 08-Nov-2010 | 1411 | BB | |
17 | Muntei | 02°49′53″S | 100°05′41″E | 4.6 | 3.4 | 3 | 08-Nov-2010 | 1411 | BB | |
18 | Muntei | 02°49′46″S | 100°05′46″E | 7.8 | 5.7 | 265 | 08-Nov-2010 | 1411 | BB | |
19 | Muntei | 02°49′53″S | 100°05′44″E | 4.6 | 3.0 | 76 | 08-Nov-2010 | 1411 | BB | |
20 | Muntei | 02°49′53″S | 100°05′44″E | 4.6 | 3.0 | 89 | 08-Nov-2010 | 1411 | RD | |
21 | Muntei | 02°49′53″S | 100°05′47″E | 5.1 | 3.6 | 133 | 08-Nov-2010 | 1411 | BB | |
22 | Muntei | 02°49′42″S | 100°05′48″E | 4.8 | 0.0 | 423 | 08-Nov-2010 | 1411 | SD | |
23 | Muntei | 02°49′50″S | 100°05′32″E | 8.8 | 08-Nov-2010 | 1628 | BB | |||
24 | Muntei | 02°49′56″S | 100°05′30″E | 6.8 | 08-Nov-2010 | 1628 | RD | |||
25 | Muntei | 02°49′57″S | 100°05′29″E | 4.5 | 08-Nov-2010 | 1628 | BB | |||
26 | Macaroni | 02°46′37″S | 99°58′59″E | 4.6 | 3.0 | 20 | 09-Nov-2010 | 0905 | BB | |
27 | Macaroni | 00°46′37″S | 99°58′59″E | 4.9 | 3.8 | 19 | 09-Nov-2010 | 0905 | BB | |
28 | Macaroni | 02°46′40″S | 99°58′57″E | 2.9 | 1.2 | 70 | 09-Nov-2010 | 0905 | MO | |
29 | Macaroni | 02°46′40″S | 99°58′57″E | 2.9 | 1.2 | 77 | 09-Nov-2010 | 0905 | MO | |
30 | Macaroni | 02°46′41″S | 99°58′58″E | 3.0 | 1.2 | 115 | 09-Nov-2010 | 0905 | MO | |
31 | Macaroni | 02°46′41″S | 99°59′01″E | 3.8 | 2.7 | 177 | 09-Nov-2010 | 0905 | BB | |
32 | Macaroni | 02°46′40″S | 99°59′00″E | 4.8 | 3.3 | 160 | 09-Nov-2010 | 0905 | BB | |
33 | Macaroni | 02°46′40″S | 99°59′00″E | 5.4 | 4.0 | 166 | 09-Nov-2010 | 0905 | BB | |
34 | Tumalei | 02°37′27″S | 99°58′48″E | 4.0 | 6 | 09-Nov-2010 | 1339 | BB | ||
35 | Tumalei | 02°37′27″S | 99°58′48″E | 5.2 | 9 | 09-Nov-2010 | 1339 | BB | ||
36 | Tumalei | 02°37′30″S | 99°58′50″E | 4.6 | 0.0 | 136 | 09-Nov-2010 | 1339 | SD, ER | |
37 | Tumalei | 02°37′25″S | 99°58′45″E | 4.7 | 46 | 09-Nov-2010 | 1425 | BB | ||
38 | Tumalei | 02°37′25″S | 99°58′45″E | 5.5 | 36 | 09-Nov-2010 | 1425 | BB | ||
39 | Tumalei | 02°37′26″S | 99°58′46″E | 6.1 | 20 | 09-Nov-2010 | 1444 | BB |
Map showing the location of survey sites (white squares). The average tsunami height at each location is shown by gray bars. For Muntei, two bars (in the village and the outer coasts) are shown. Locations (according to USGS) of the mainshock (black triangle) and aftershocks (gray circles), which occurred within 1 day of the mainshock, are also shown
3 Tsunami Height Distributions
3.1 Asahan and Purorougat
On the Asahan coast, facing the mouth of a ~2-km-wide bay on the west coast of South Pagai Island, a large coral boulder (~1 m diameter) was transported ~70 m beyond a beach ridge of ~3 m altitude. Traces on trees indicated tsunami heights of 6.4–9.3 m, with an average of 7.4 m (Fig. 6a). These were the largest tsunami heights measured by our survey. On the contrary, in Asahan village, located near the head of the bay, no tsunami damage occurred. At Purorougat, facing a smaller (~0.5 km wide), U-shaped bay, the tsunami washed away most houses, and 75 out of 235 residents lost their lives. A trace on a tree indicated a flow depth of ~5.5 m.
3.2 Lopon Lakau
Located in a bay ~2 km wide on the southwest coast of South Pagai Island, Lopon Lakau (a logging port) was damaged by the tsunami. Numerous coral boulders were found on the beach, and a trace on a tree indicated a 2.5-m tsunami height. At Lakau village, an eyewitness recounted that the ground shaking was strong enough for him to be awakened. Having heard an airplane-like loud noise, villagers escaped inland, and all survived.
3.3 Maonai
Topographic profile (thick solid lines) and tsunami heights (gray circles) at five locations. Solid gray lines represent simulated water levels using one-dimensional computation from input waveforms of linear computation, while dashed gray lines represent simulated water levels from input waveforms of nonlinear computation (see Sect. 3.5)
Photographs of the effects of the tsunami at: a Asahan, b Maonai, c Sabeu Gunggung, d Muntei, e Macaroni Resort, and f Tumalei
3.4 Sabeu Gunggung
Located on the end of a U-shaped bay (~3 km wide) on the southwestern coast of North Pagai Island, this village suffered significantly from the tsunami. We surveyed a profile up to ~300 m from the coast, but could not reach the inundation limit because of the river in the back of the village. The tsunami height was 4.3–7.0 m (average of four measurements was 5.5 m) measured on a surface ~2 m above the sea level (Fig. 5b). The flow depth ranged from 3.9 to 4.8 m. There had been 65 houses, but none remained. Of the original population of 260, 120 people lost their lives (Fig. 6c). According to a survivor, ground shaking was not strong, and he escaped after hearing a loud sound ~5 min after the shaking. Some people were watching TV and saw running text of a tsunami warning, but the tsunami was arriving at that time.
3.5 Muntei Barubaru
Located ~5 km SE of Sabeu Gunggung, this village faces into a small V-shaped bay approximately 1 km wide. The inundation distance was ~420 m, with a run-up height of 4.8 m: the tsunami heights ranged from 4.6 to 5.7 m with one exceptional measurement of 7.8 m (Fig. 5c). The average of the eight measurements was 5.2 m. Many large (~2 m diameter) coral boulders were also transported onto land, and the entire village was washed away (Fig. 6d). Of the original population of 310, 149 lost their lives. On the opposite (western) side of the bay, traces on trees indicate tsunami heights ranging from 3.9 to 8.8 m, with an average of 6.0 m of the four measurements.
3.6 Macaronis Resort
Located on a ~2-km-long peninsula, extending in the SW direction, at the western tip of North Pagai Island, this resort consisted of a main hotel tower (Fig. 6e), several single-story buildings, and beach cottages. The main tower was damaged on the ground floor; however, it remained standing while the second and higher floors provided shelter for approximately 20 guests, all of whom survived. The cottages on the beach were all washed away, and the buildings were also damaged. We surveyed across the peninsula (Fig. 5d) and found that the tsunami arrived from both directions. Clear watermarks on the building indicated that the flow depth was ~1.2 m on the peninsula (~2 m above sea level). Higher tsunami traces ranging from 2.9 to 5.4 m were found on trees, with an average tsunami height of 4.0 m based on eight measurements.
3.7 Tumalei
Located on the northwest coast of North Pagai Island, in a small bay facing north, the main village, with a population of approximately 200, was on a flat area ~100 m wide flanked by a steep hill. The tsunami height ranged from 4.0 to 6.1 m, and the average of six measurements was 5.0 m. The inundation distance was ~140 m to the hill slope (Fig. 5e). Most houses were washed to the base of the hill, but some were not completely broken (Fig. 6f). Given the proximity to the hill, the residents spontaneously escaped to high ground. In addition, tsunami education and training had been conducted by national and foreign Non-Governmental Organizations (NGOs), such as TimPB and SurfAID, with four drills since 2008. These factors contributed to the small number of fatalities.
4 Tsunami Modeling
4.1 Observed Tsunami Waveforms
Locations of tide gauge, GPS buoy, and DART stations used for the inversion. Rectangle shows the computation area with a 12″ grid interval for a near-field tsunami propagation. The focal mechanism of the USGS W-phase moment tensor solution is also shown
Tsunami waveforms recorded at the coastal tide gauge, GPS buoy, and DART stations (black solid curves), and computed from our final model (gray dashed curves). The locations of the gauges are shown in Fig. 7. Thick gray bars above the time axis indicate the time range used in the inversions to match the observed and synthetic waveforms. The waveforms at stations without bars (Cilacap, Trinconmalee, Rodrigues, Port Luis and Point La Rue) are not used for inversion
Within 10 min of the earthquake, the Mentawai buoy recorded two pulses of tsunami waves with amplitudes of ~15 cm and a period of a few minutes. At Padang, the nearest tide gauge station, the tsunami started with a small negative pulse at approximately 1 h after the earthquake, followed by a crest of ~0.3 m. The tsunami amplitudes were mostly <0.1 m at other stations in Indonesia, Sri Lanka, and Maldives. Notable exceptions were at Rodrigues and Port Louis (Mauritius) where a second wave with ~0.2 m amplitude arrived ~6 and ~7 h after the earthquake, respectively. The tsunami was also recorded at La Reunion Island with amplitude ~0.2 m (Sahal and Morin 2012). At the DART station, the tsunami arrived at ~2 h after the earthquake with an amplitude of just 0.01 m.
4.2 Tsunami Computation and Bathymetry Data
We carried out three types of tsunami numerical computations. The first one was in the entire Indian Ocean for the inversion of the observed tsunami waveforms to estimate the earthquake slip distribution (Sect. 3.3). The second one was a more detailed computation around the Pagai Islands with tsunami inundation to compare with the measured tsunami heights (Sect. 3.4). The third type involved a one-dimensional computation based on the measured topographic profiles at selected sites (Sect. 3.5).
For the tsunami propagation in the Indian Ocean, we computed tsunami waveforms by using linear computations on a spherical coordinate system (Satake 1995). The computational region is as shown in Fig. 7 with grid interval of 2′ (~3.7 km). Near the tide gauge stations, finer (24″, ~0.74 km) grids were adopted. The bathymetric data was resampled from GEBCO_08 30″ gridded data. Around the Indonesian tide gauge stations (Padang, Enggano, Tanahbalah, and Telukdalam), we made 12″ (~0.37 km) grid data from GEBCO_08 and Indonesian Navy charts.
For the computations around the Pagai Islands, we used a system of nested grids. The largest domain that included the source region had a 27″ (~833 m) grid, while the finest domain had a 1″ (~30 m) grid. For the coarser domains (27″ and 9″), the linear shallow-water equations were used, while at the finer domains (3″ and 1″), both linear computation and nonlinear computation with inundation were made. For these detailed computations, we merged ETOPO1 data with Indonesian Navy chart data at the 200-m contour depth, and modified the coastline and SRTM data, as described below.
For the one-dimensional tsunami inundation simulations along the surveyed transect lines, the nonlinear shallow-water equations were solved using a finite difference scheme in the Cartesian coordinate system (Gusman et al., 2012). For this computation, tsunami waveforms computed in the detailed simulation at points several hundreds meters from the shoreline at a water depth of ~5 m were used as input waveforms. Tsunami inundation along a surveyed topographic profile was computed with a 1-m grid size.
Nearshore bathymetry data around the Pagai Islands. a GEBCO_08 data. b Digitized Navy charts (241, 242, and 277)
For the topography data of the Pagai Islands, we compared the Shuttle Radar Topography Mission (SRTM) data (1″ grid) provided by the US National Aeronautics and Space Administration (NASA) with topographic profile data obtained through a field survey, and found that the SRTM data were consistently higher by several meters, likely because of the vegetation effects. Therefore, we reduced 7 m in elevation from the SRTM data to form the topography data and then merged this with the bathymetry data.
4.3 Tsunami Inversion and Slip Distribution
Fault parameters and slip amounts of subfaults for the inversion
No. | Length (km) | Width (km) | Depth (km) | Strike (deg) | Dip (deg) | Rake (deg) | Slip (m) | Lat (deg) | Long (deg) |
---|---|---|---|---|---|---|---|---|---|
1 | 30 | 30 | 2 | 326 | 7.5 | 101 | 1.83 | −4.34144 | 100.10976 |
2 | 30 | 30 | 2 | 326 | 7.5 | 101 | 0.00 | −4.11777 | 99.95845 |
3 | 30 | 30 | 2 | 326 | 7.5 | 101 | 1.16 | −3.89410 | 99.80719 |
4 | 30 | 30 | 2 | 326 | 7.5 | 101 | 6.10 | −3.67043 | 99.65597 |
5 | 30 | 30 | 2 | 326 | 7.5 | 101 | 0.00 | −3.44675 | 99.50480 |
6 | 30 | 30 | 2 | 326 | 7.5 | 101 | 3.81 | −3.22308 | 99.35366 |
7 | 30 | 30 | 2 | 326 | 7.5 | 101 | 1.02 | −2.99941 | 99.20255 |
8 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 0.14 | −4.19186 | 100.33215 |
9 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 3.25 | −3.96819 | 100.18078 |
10 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 3.06 | −3.74452 | 100.02946 |
11 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 3.01 | −3.52085 | 99.87819 |
12 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 3.79 | −3.29718 | 99.72696 |
13 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 4.96 | −3.07351 | 99.57577 |
14 | 30 | 30 | 5.92 | 326 | 7.5 | 101 | 0.00 | −2.84983 | 99.42461 |
15 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.00 | −4.04228 | 100.55451 |
16 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.00 | −3.81861 | 100.40307 |
17 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.00 | −3.59494 | 100.25170 |
18 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.00 | −3.37127 | 100.10037 |
19 | 30 | 30 | 9.83 | 326 | 12 | 101 | 3.34 | −3.14760 | 99.94908 |
20 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.00 | −2.92393 | 99.79784 |
21 | 30 | 30 | 9.83 | 326 | 12 | 101 | 0.42 | −2.70026 | 99.64665 |
22 | 30 | 30 | 16.07 | 326 | 12 | 101 | 1.97 | −3.89471 | 100.77383 |
23 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.00 | −3.67104 | 100.62234 |
24 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.00 | −3.44737 | 100.47091 |
25 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.12 | −3.22370 | 100.31953 |
26 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.00 | −3.00003 | 100.16820 |
27 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.00 | −2.77636 | 100.01691 |
28 | 30 | 30 | 16.07 | 326 | 12 | 101 | 0.00 | −2.55268 | 99.86567 |
Slip distributions estimated by the inversion a and computed seafloor deformation b. The subfault number (Table 2), the epicenter (blue star), aftershocks (red), and the slip distribution of the 2007 Bengkulu earthquake (Fujii and Satake 2008) are shown in a. Contour interval in (b) is 0.2 m for uplift (red) and 0.1 m for subsidence (dashed blue)
Slip on the shallow subfault ranged from 1 to 6 m, while slip on the deep subfaults was smaller. The maximum computed slip of 6.1 m was somewhat smaller than that estimated from seismic wave analysis (4.5 to 9.6 m; Lay et al., 2011; Bilek et al., 2011; Newman et al., 2011) or from the GPS and tsunami modeling (9.7 m; Hill et al., 2012), although the size of slip patches of the above analyses was smaller. The seismic moment was computed as 1.0 × 1021 Nm, assuming the rigitidy of 3 × 1010 N/m2. The corresponding moment magnitude was Mw = 7.9.
4.4 Detailed Simulations Around Pagai Islands
Computed coastal tsunami heights by using the fine-scale bathymetry (9″) and linear equation. The gray bars and colors show the computed nearshore heights. The red bars show the measured heights. Areas for nested grids (3″ and 1″) with nonlinear computations with inundation are also shown
Comparison of the measured tsunami heights with the computed nearshore heights within 500 m of the measurement points showed that they are similar at most locations. At Maonai, the computed heights ranged from 4.9–8.1 m, while the measured heights ranged from 6.7–7.3 m. On North Pagai Island, the computed heights ranged from 2.8 to 6.5 m at Tumalei (measured heights are 4.0–6.1 m), from 2.2 to 3.8 m at Macaronis resort (measured heights are 2.9–5.4 m), from 2.0–4.0 m at Muntei Barubaru (measured heights are 4.6–5.7 m in the village and 3.9–8.8 m on the western side), and from 3.0–6.8 m in Sabeu Gunggung (measured heights are 4.3–7.0 m). An exception is at Asahan where the computed heights ranging from 1.8 to 3.1 m were much smaller than the measured heights ranging from 6.4 to 9.3 m.
Computed tsunami inundation areas (color) and comparisons of measured and computed tsunami heights (red and blue bars, respectively) at Muntei Barubaru, Sabeu Gunggung, and Macaroni Resort on the finest grid (1″). One-dimensional computations (Sect. 3.6) are made along the dashed lines, using the input waveforms computed at offshore points shown by red squares. White circles show the topographic profiles based on our field measurements (Fig. 5)
4.5 One-dimensional Inundation Computations
The tsunami run-up heights along the measured topography profiles were computed and compared with the measured tsunami heights (Fig. 5). The waveforms calculated at offshore points of Sabeu Gunggung, Muntei, and Macaroni Resort on a 1″ grid with linear and nonlinear computations, at Tumalei on a 3″ grid with linear and nonlinear computations, and at Maonai on a 9″ grid with linear computations were used as input for the 1D computation. When the linear input waveforms were used, the computed tsunami inundation heights were mostly similar or larger than the measured heights projected on the profile, except at Sabeu Gunggung. Considering that not all the measured points were located on the profile, the agreement was rather satisfactory. When the nonlinear input waveforms were used, the computed inundation heights were somewhat smaller than the measured heights. The discrepancy came from the different amplitudes of input waveforms. The amplitudes on the 1″ grid were smaller than those on the 9″ grid by a factor of 1–1.7; the nonlinear computation produced smaller amplitudes than the linear computation.
5 Conclusions
- 1.
Tsunami heights were measured at eight locations on the west coast of North and South Pagai Islands. Thirty-eight measurements ranged from 2.5 to 9.3 m, but mostly 4–7 m. The tsunami inundation distance was more than 300 m at three locations. Our survey was made within 2 weeks of the earthquake, when sea conditions were very rough, making land access difficult. Later surveys (Kerpen et al., 2011; Hill et al., 2012) covered larger areas and reported more extreme tsunami heights.
- 2.
This earthquake was a tsunami earthquake, one that produces weak ground shaking but large tsunamis. Residents reported that the ground shaking was weaker than during the 2007 Bengkulu or the 2009 Padang earthquake.
- 3.
The official tsunami warning from BMKG reached the Mentawai regency office, but did not reach coastal communities because of the lack of communication infrastructure. However, some coastal residents were watching TV and saw running text of a tsunami warning 5–18 min after the earthquake, according to BMKG (2010).
- 4.
Inversion of tsunami waveforms indicated the slip was larger at offshore subfaults, with a maximum of 6.1 m. In particular, the nearby surface GPS buoy recorded two pulses of tsunami waves, probably from two large slip regions at shallower subfaults.
- 5.
The nearshore tsunami heights computed from the above source model using the fine-scale bathymetry (9″) and linear equations were roughly similar to our measured heights. Tsunami inundation heights computed on a 1″ grid using nonlinear equations were smaller than the measured heights, probably because of inaccurate bathymetry and topography. The one-dimensional computations using measured profiles reduced the discrepancy.
Notes
Acknowledgments
This survey was made as a part of the SATREPS “Multi-disciplinary natural hazard reduction from earthquakes and volcanoes in Indonesia” project supported by the JST (Japan Science and Technology Agency) and JICA (Japan International Cooperation Agency), as well as RISTEK and LIPI. Among the authors, KS, YN, PSP, HS, and EY conducted the survey. We thank Pariatmono, Mulyo Harris Pradono, Atsushi Koresawa, and Megumi Sugimoto, who also joined the survey to study the reactions of residents. We thank Jody Bourgeois for reading and commenting on the results of the field survey. The tsunami waveform analysis and simulations were conducted by KS, ARG, HS, TF, HL, and YT. In particular, YF took the lead in tsunami waveform inversion, HS in detailed simulation, and ARG in one-dimensional computation. We respect and appreciate the efforts of the operators of the costal tide gauge stations, DART and GPS buoy stations. The buoy data were provided to us by Wahyu Pandoe of BPPT and Tilo Schoene at GFZ. We also thank Jose Borrero, two anonymous reviewers, and Herman Fritz for their comments on the final manuscript.
Open Access
This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
References
- Badan Meteorologi Klimatologi dan Geofisika (2010), Laporan Gempabumi Mentawai, 25 Oktober 2010, 18 pp.Google Scholar
- Bilek, S.L., Engdahl, E.R., DeShon, E.R., and Hariri, M.E. (2011), The 25 October 2010 Sumatra tsunami earthquake: Slip in a slow patch, Geophys. Res. Lett., 38, L14306, doi: 10.1029/2011GL047864.
- Borrero, J.C., Weiss, R., Okal, E. A., Hidayat, R., Suranto, Arcas, D., and Titov, V. (2009), The tsunami of 2007 September 12, Bengkulu province, Sumatra, Indonesia: post-tsunami field survey and numerical modeling, Geophys. J. Int., 178, 180–194.Google Scholar
- Fritz, H.M., Kongko, W., Moore, A., McAdoo, B., Goff, J., Harbitz, C., Uslu, B., Kalligeris, N., Suteja, D., Kalsum, K., Titov, V., Gusman, A., Latief, H., Santoso, E., Sujoko, S., Djulkarnaen, D., Sunendar, H., and Synolakis, C.E. (2007), Extreme runup from the 17 July 2006 Java tsunami, Geophys. Res. Lett., 34, L12602, doi: 10.1029/2007GL029404.
- Fujii, Y., and Satake, K. (2006), Source of the July 2006 West Java tsunami estimated from tide gauge records, Geophys. Res. Lett., 33, L24317, doi: 10.1029/2006GL028049.
- Fujii, Y., and Satake, K. (2007), Tsunami source of the 2004 Sumatra-Andaman Earthquake inferred from tide gauge and satellite data, Bull. Seism. Soc. Am., 97, S192–S207.Google Scholar
- Fujii, Y., and Satake, K. (2008), Tsunami waveform inversion of the 2007 Bengkulu, southern Sumatra, earthquake, Earth, Planets Space, 60, 993–998.Google Scholar
- Gusman, A. R., Tanioka, Y., and Takahashi, T. (2012), Numerical experiment and a case study of sediment transport simulation of the 2004 Indian Ocean tsunami in Lhok Nga, Banda Aceh, Indonesia, Earth Planets Space, (in press).Google Scholar
- Hill, E.M., Borrero, J.C., Huang, Z., Qiu, Q., Banerjee, P., Natawidjaja, D.H., Elosegui, P., Fritz, H.M., Suwargadi, B.W., Pranantyo, I.R., Li, L.-L., Macpherson, K.A., Skanavis, V., Synolakis, C.E., and Sieh, K. (2012), The 2010 Mw 7.8 Mentawai earthquake: very shallow source of a rare tsunami earthquake determined from tsunami field survey and near-field GPS data, J. Geophys. Res. 117, B06402, doi: 10.1029/2012JB009159.
- Kerpen, N.B., Kongko, W., Kramer, K.D.D., Goseberg, N., and Schlurmann, T. (2011), International post-tsunami survey related to the October 25th, 2010 Mentawai tsunami, GFZ German Research Centre for Geoscience, Report –Nr. 716, 31 pp.Google Scholar
- Lay, T., Ammon, C.J., Kanamori, H., Yamazaki, Y., Cheung, K.F., and Hutko, A.R. (2011), The 25 October 2010 Mentawai tsunami earthquake (M w 7.8) and the tsunami hazard presented by shallow megathrust ruptures, Geophys. Res. Lett., 38, L06302, doi: 10.1029/2010GL046552.
- Natawidjaja, D.H., Sieh, K., Chlieh, M., Galetzka, J., Suwargadi, B.W., Cheng, H., Edwards, R.L., Avouac, J-P., and Ward, S.N. (2006), Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls, J. Geophys. Res., 111. B06403, doi: 10.129/2055JB004025.
- Newman, A.V., Hayes, G., Wei, Y., and Convers, J. (2011), The 25 October 2010 Mentawai tsunami earthquake, from real-time discriminants, finite-fault rupture, and tsunami excitation, Geophys. Res. Lett., 38, L05302, doi: 10.1029/2010GL046498.
- Okada, Y. (1985), Surface deformation due to shear and tensile faults in a half-space, Bull. Seism. Soc. Am., 75, 1135–1154.Google Scholar
- Putra, P. S., Nishimura, Y., and Yulianto, E. (2012), Sedimentary features of tsunami deposits in carbonate-dominated beach environments: a case study from the 25 October 2010 Mentawai Tsunami, Pure Appl. Geophys. (in press).Google Scholar
- Sahal, A. and Morin, J. (2012). Effects of the October 25, 2010, Mentawai tsunami in La Réunion Island (France): observations and crisis management, Nat. Hazards, 62, 1125–1136, doi: 10.1007/s11069-012-0136-2.
- Satake, K. (1995), Linear and nonlinear computations of the 1992 Nicaragua earthquake tsunami, Pure Appl. Geophys., 144, 455–470.Google Scholar
- Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C.-C., Cheng, H., Li, K.-S., Suwargadi, B.W., Galetzka, J., Philibosian, B., and Edwards, R.L. (2008), Earthquake supercycles inferred from sea-level changes recorded in the corals of West Sumatra, Science, 322, 1674–1678.Google Scholar
- Singh, S.C., Hananto, N., Mukti, M., Permana, H., Djajadihardja, Y., and Harjono, H. (2011), Seismic images of the megathrust rupture during the 25th October 2010 Pagai earthquake, SW Sumatra: frontal rupture and large tsunami, Geophys. Res. Lett., 38, L16313. doi: 10.1029/2011GL048935.
- Tanioka, Y. and Satake, K. (1996), Tsunami generation by horizontal displacement of ocean bottom, Geophys. Res. Lett., 23, 861–864.Google Scholar
Copyright information
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.