Descriptive Model of the July 17, 1998 Papua New Guinea Tsunami

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The tsunami that struck New Guinea on July 17, 1998 was the most devastating tsunami since the 1976 Moro Gulf, Philippines, tsunami and may surpass that event (Lockridge and Smith, 1984; Satake and Imamura, 1995). The high reported runups and the tremendous loss of life are of great concern to all, including the international scientific community. Scientists closely examined this event in hopes of mitigating such disasters in the future.

Illustration of coastline where a disturbance has caused the ocean water to begin rippling.

Snapshot from a preliminary simulation of the 1998 New Guinea tsunami.

Simplistic map shows islands and fault lines are drawn on top with a star at the location of a 1998 earthquake.

Star shows the epicenter of the 1998 earthquake. Figure modified from Abers and McCaffrey (1988) 

 

Related Publications

  1. Geist, E. L., 1998, Source characteristics of the July 17, 1998 Papua New Guinea tsunami: EOS, Transactions of the American Geophysical Union, v. 79 (supplement), p. 571.
  2. Geist, E. L., 1999, Local tsunamis and earthquake source parameters, Advances in Geophysics, v. 39, p. 117-209.

Background

The tsunami that struck New Guinea on July 17, 1998 was the most devastating tsunami since the 1976 Moro Gulf, Philippines, tsunami and may surpass that event (Lockridge and Smith, 1984; Satake and Imamura, 1995). The high reported runups and the tremendous loss of life are of great concern to all, including the international scientific community. Scientists closely examined this event in hopes of mitigating such disasters in the future.

New Guinea is a seismically active region, the site of an arc-continent collision, where tectonic plates are converging and sliding past each other. The tectonic boundaries and faulting in this region are very complex.

A comprehensive discussion and listing of historical earthquakes and tsunamis in the region can be found at the Russian Academy of Sciences' Tsunami Laboratory and in an article by Everingham (1974).

Global map showing all the continents with the focus on New Guinea and the 1998 earthquake

Cartoon showing beachballs pointing to locations on a map, balloons represent the mechanics behind an earthquake.

 

The Earthquake

The recorded magnitude of the earthquake was 7.1 (corrected to 7.6), and the epicenter was located in northern New Guinea near the coast. The fault mechanism from the National Earthquake Information Center (NEIC) shown by the red-and-white ball indicates that the earthquake could have occurred as uplift on a vertical fault or sliding on a horizontal fault. The inset in the upper right corner of the figure shows the location of the epicenter.

The source mechanisms for previous shallow earthquakes in the region display a remarkable diversity in the type of faulting. (Read an explanation of "beachball" diagrams.) Near the July 17, 1998 event, however, most of the events are along steeply dipping reverse faults. Note the similarity in mechanism between the 5/14/82 event and the 7/17/98 event. Mechanisms to the south and east are mostly strike-slip events, whereas mechanisms to the west are mostly normal faulting events.

Earthquakes from the Harvard Condensed Matter Theory (CMT) Group (see also, Harvard Seismology) catalog shallower than 30 km in the vicinity of the July 17, 1998 event. Note that the location of the July 17, 1998 event determined by the Harvard CMT group differs from the NEIC location. Earthquakes occurred between 3/4/79 and 7/17/98 and ranged in magnitude between 5.1 and 7.1, the largest being the July 17, 1998 event.

Illustration showing water depth and land height in varying shades of different colors, to simulate a 3-D appearance.

Bathymetry

The bathymetry indicates that just offshore of the northern coast of New Guinea there is very steep and linear slope. It is possible that the relatively deep water near shore contributed to the unusual height of this tsunami. Shown here is the bathymetry in the region contoured at 200 m intervals from the 2-minute bathymetric data of Smith and Sandwell (1997) (Copyright).

In this figure, black circles indicate locations for the earthquake determined by the NEICHarvard, and the Earthquake Research Institute (ERI) at the University of Tokyo.

The Tsunami

At present, too little is known about the July 17, 1998 earthquake and about the distribution of runup to formulate a quantitative model of the tsunami. The reported runups are unusually large for an earthquake of magnitude 7.1 (cf. Geist, 1998). Below, a descriptive or qualitative simulation of the tsunami is computed by making several assumptions about the source parameters of the earthquake. The model is for descriptive purposes only—a quantitative model awaits more information on the exact location of the earthquake and accurate measurements of runup. Of equal importance, the grid size used in this simulation is quite large and does not capture the nearshore behavior of the tsunami (cf. Titov and Synolakis, 1997). A full description of the assumptions and specifications of this model is listed below.

About the Animation

The animation shows how the July 17 tsunami might have looked from a vantage point above Papua New Guinea. The coastline shown in the animation is about 550 kilometers (340 miles) long.

The animation begins with the initial wave—which formed almost simultaneously with the earthquake that triggered the event—and shows how the initial wave was reflected from the island. Note other waves traveling east and west along the coast.

Animated cartoon shows a 3-D representation of tsunami waveforms and how they move around islands and seafloor features.

This animation does not show runup—the maximum elevation the water reached as it rose above the shoreline. Based on very preliminary data, this animation is a "descriptive model" of the tsunami. A more accurate simulation, or "quantitative model", can be developed when accurate measurements of the runup and more information about the earthquake that triggered the tsunami become available.

Please note that for display purposes, the tsunami wave heights in the animation are greatly exaggerated with respect to the bathymetry.

Although this animation graphically indicates the evolution of this tsunami, the simulated offshore wave heights are much less than the reported runups. Among international scientists, more highly refined models will be developed on the basis of higher resolution bathymetry, measured runup and inundation distributions, seismic source models, and more accurate representation of the hydrodynamics. As these models are developed and come online, links will be reported here.

Waveform modeling and comparison with observed records of the tsunami (NOAA)

A man crouches near a small trench dug into sand and he is pointing with a trowel to show the contact with pre-tsunami debris.

More Information About the Papua New Guinea Tsunami

  • Preliminary Analysis of Sedimentary Deposits from the 1998 Papua New Guinea Tsunami (link coming soon)
  • Tide gauge records, simulations, and links to more web sites from NOAA
  • Preliminary report from the 1st International Tsunami Survey Team
  • Earthquake information for this event from USGS

Descriptive Model of the July 17, 1998 Papua New Guinea Tsunami:

Assumptions and Specifications for Animations

Hydrodynamic Model:

  • A linearized form of the shallow-water wave equations was used to simulate the tsunami. Because non-linear terms were not included, the computations are probably only accurate for water depths deeper than 50 m.
  • The computations were performed on a 3.7 km grid at a time interval of 10 seconds. Although the model is stable, the nearshore evolution of the tsunami is not accurately portrayed because of the large grid size.
  • The model does not compute runup or inundation.

Earthquake Source Model:

  • Because only the location, depth, and seismic moment of the event are known at this time, certain assumptions must be made to determine the rupture area and slip.
  • Slip on the vertical plane is assumed.
  • An empirical relationship is used to determine the rupture area from the seismic moment (Wells and Coppersmith, 1994). An assumed 3:2 aspect ratio (length:width) yields the dimensions of the rupture zone.
  • Using the assumed rupture area (above) and a shear modulus of 30 GPa results in an average slip of 2.15 m.
  • Assuming uniform slip typically underestimates the tsunami that is produced (Geist, 1998). Therefore, an arbitrary and symmetric slip distribution is assumed that averages to 2.15 m.
  • Because this was a very shallow event, the rupture extends to the seafloor.
  • A 10 second rise time is assumed, making this a nearly impulsive event with respect to tsunami propagation speeds.
  • Because of the steep bathymetric gradient, errors in the epicenter location result in significant changes to the tsunami time history. The Harvard centroid location is used.

References Cited

Abers, G., and R. McCaffrey, 1988. Active deformation in the New Guinea fold-and-thrust belt: Seismological evidence for strike-slip faulting and basement-involved thrusting, J. Geophys. Res., v. 93, p. 13,332-13,354.

Everingham, I.B., 1974. Large earthquakes in the New Guinea-Solomon Islands area, 1873-1972, Tectonophysics, v. 23, p. 322-338.

Geist, E. L., 1998. Local tsunamis and earthquake source parameters, Advances in Geophysics, v. 39, p. 117-209.

Lockridge, P. A., and R. H. Smith, 1984. Tsunamis in the Pacific Basin, 1900-1983. National Geophysical Data Center, Boulder, Colorado. Scale 1:17,000,000.

Smith, W. H. F., and Sandwell, D. T., Science, v. 277, p. 1956.

Satake, K., and F. Imamura, 1995. Tsunamis 1992-1994. Pure and Applied Geophysics, v. 144, p. 373-379.

Titov, V. V., and C. E. Synolakis, 1997. Extreme inundation flows during the Hokkaido-Nansei-Oki tsunami, Geophys. Res. Lett, v. 24, p. 1315-1318.

Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.

Smith and Sandwell 1997 Copyright

Walter H. F. Smith and David T. Sandwell, Copyright 1997

Please copy and use these digital topography files for your applications. We are not responsible for errors in the depths. The depths have limited accuracy and should not be used for navigation.

The data contained in this digital file should not be used in any product sold for profit without the written consent of the authors.

Consent is not required for non-profit research use or for creating graphics for oral or poster presentations.

The appropriate reference for these data is: Smith, W. H. F. and Sandwell, D. T., Global Seafloor Topography from Satellite Altimetry and Ship Depth Soundings, submitted to Science, April 7, 1997.

This copyright text must be copied and placed in the same directory as the digital data file. In addition, the copyright must be attached to any derivative digital topography grids that are intended for re-distribution. Our objective is to have the data distributed as widely as possible, but not sold.

This copyright also applies to the Land Elevation data.

Metadata for bathymetry
Originator: United States Geological Survey (USGS), Coastal and Marine Geology (CMG), Primary

Investigator (Eric L. Geist)
Publication_Date: 19990729
Title: Bathymetry, offshore of the northern coast of New Guinea

Description:
Abstract: Figure displays earthquake locations plotted on ETOPO bathymetric data of the northern coast of New Guinea contoured with GMT software.

Purpose: These data and information are intended for science researchers, students from elementary through college, policy makers, and general public. Figure intended both to illustrate bathymetric relief just offshore of the northern coast of New Guinea and to supplement discussion of the 1998 New Guinea tsunami.

Supplemental_Information: Figure created using a UNIX C Shell script to run GMT V3.3.1 on a SUNW,Ultra-2 platform with a sparc processor running the SunOS operating system release 5.7. Final PostScript to GIF work done using Adobe Illustrator 8.0.1 on a Power Macintosh G3 running Mac OS 8.1.

Information from GMT grdinfo report:

Title - Data from Altimetry

Remark: Spherical Mercator Projected with -Jm1 -R140/145/-4.03000629166/0

Pixel node registation used
grdfile format # 0
x_min: 0.00000 x_max: 5.00000 x_inc: 0.03333
units: Spherical Mercator projected Longitude, -Jm1, length from West Edge. nx: 150
y_min: 0.00000 y_max: 4.03333 y_inc: 0.03333
units: Spherical Mercator projected Latitude, -Jm1, length from South Edge. ny: 121
z_min: -4588.00000 z_max: 1996.00000
units: meters, mGal, Eotvos, or micro-radians, depending on img file and -S.
scale_factor: 1.00000 add_offset: 0.00000

Reference for ETOPO DATA
Smith, W. H. F., and Sandwell, D. T., 1997, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1956-1962.
Data link found at http://topex.ucsd.edu/sandwell/sandwell.html#Sandwell
Data info found at http://topex.ucsd.edu/marine_topo/mar_topo.html

Reference for GMT SOFTWARE
Wessel, P., and Smith, W. H. F., 1998, New, improved version of Generic Mapping Tools released, EOS Trans. Amer. Geophys. U., v. 79 (47), p. 579.
Software citation found at http://imina.soest.hawaii.edu:80/wessel/wessel_pubs.html
Software info found at http://imina.soest.hawaii.edu/gmt/

Time_Period_of_Content: Calendar_Date: 19990729
Spatial_Domain: Bounding_Coordinates:
West_Bounding_Coordinate: 140.00000
East_Bounding_Coordinate: 145.00000
North_Bounding_Coordinate: 0.00000
South_Bounding_Coordinate: -4.00000

Place_Keyword: New Guinea
Place_Keyword: Pacific Ocean

Use_Constraints: Please recognize the U.S. Geological Survey (USGS) as the source of this information. Some USGS information accessed through this means may be preliminary in nature and presented without the approval of the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the responsibility of the user. This information is not intended for navigational purposes. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Point_of_Contact:
Contact_Organization: United States Geological Survey (USGS), Coastal and Marine Geology (CMG)
Contact_Person: Eric L. Geist
Contact_Position: Geophysicist
Address: USGS, MailStop 999, 345 Middlefield Road, Menlo Park, CA 94025-3561 USA
Contact_Voice_Telephone: (650) 329-5457
Contact_Facsimile_Telephone: (650) 329-5411
Contact_Electronic_Mail_Address: egeist@usgs.gov