Hawaii (HAW)

Authors:

F. W. Klein, A.D. Frankel, C.S. Mueller, R.L. Wesson, P.G. Okubo

Summary

The Global Hazard Mosaic coverage of Hawaii is based on the 1998 United States Geological Survey (USGS) model of Klein et al., (2001). The GEM implementation relies on the best judgement of the Secretariat in converting the documented model into the OpenQuake (OQ) engine format from the NSHMP input files provided by the USGS.

Information about the OQ model versions and input files can be found on the Results and Dissemination page.

Interactive Viewer

The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.

viewer_legend

Regional Tectonics

Most of the seismicity in Hawaii is associated with active rifting and volcanism. The largest earthquakes occur as the result of compressive stresses along sub-horizontal flank faults (basal decollments) along the volcanoes Mauna Loa, Kilauea, and Hualalai, posing the highest hazard to the southernmost Big Island of Hawaii. The most active flanks are those that are seaward and unbuttressed. Seismicity also occurs within the rift zones bounding the flanks, and in the Kilauea Caldera. Throughout the entire island chain, seismicity occurs due to flexural loading of the crust, and rates diminish with volcanic activity to the northwest. Deeper seismicity also occurs within the magma chambers.

Basic Datasets

Please refer to Klein et al., 2001 for an explanation of the datasets and methodology used to build the model.

Seismic Source Characterisation

The source model utilizes five groups, which include sub-models based on magnitude (Table 1 of Klein et al., (2001)). We summarize these here.

  • Flank zones (complex faults and point sources) that can presumably rupture in a single earthquake
  • Uniform seismicity (area sources) in the rift zones and Kilauea Caldera
  • Smoothed shallow seismicity (point sources) in other areas of Hawaii Island
  • Smoothed deep seismicity (point sources) beneath Hawaii Island
  • Smoothed shallow seismicity (point sources) that ramps downward away from the active volcanism (to the northwest)

All source groups model earthquakes with Mmin 5.0 and a variable Mmax, using different source types for different magnitude ranges. For each group and magnitude range, occurrence rates are derived using the truncated Gutenberg-Richter approach. This methodology extends to the flank zones in Group 1, despite the authors' recognition that the driving stresses are not spatially or temporally constant.

All sources are given full weighting in a single logic tree branch.

Flank zones

The flank zone group includes five perimeters (HLE, HUA, KAO, KON, SFL) that bound the supposed rupture areas of historic earthquakes (see Klein et al., (2001), Figures 1, 2). The rupture areas are subhorizontal at a depth of ~10 km. The source model uses the perimeters as area sources for M<6.5, and complex faults for M6.5-7.0. Additionally, the three nearly continuous flanks in the southeastern Hawaii Island are linked together to form a single complex fault capable of earthquakes M7.0-8.2. For area sources, hypocenters were fixed at 10 km depth. All sources use a purely reverse mechanism. The occurrence rate properties are listed in Table 1, which is a summary of source properties from Table 3 in Klein et al., (2001). Flank zones modelled individually are assigned the tectonic region of "Volcanic", while the combined source is called "Volcanic Large".

Flank zone a-Value b-Value M range
HLE 1.7255 0.5713 5.0-7.0
HUA 2.6318 0.7306 5.0-7.0
KAO 1.8810 0.5713 5.0-7.0
KON 0.3413 0.3100 5.0-7.0
SFL 2.1720 0.5700 5.0-7.0
HLE-KAO-SFL 2.4329 0.5713 7.0-8.2

Kilauea Caldera and rift zones

The three area sources of the Kilauea Caldera and rift zones (CAL, SWR, ERZ) are modeled as grids of point sources with 0.02°-spacing and magnitudes up to M6.5. Table 2 lists the occurrence rate properties, and is based on Table 3 in Klein et al. (2001). a-Values are for the entire area source, and thus in the source model, the available moment is divided among the point sources. The tectonic region type is volcanic.

Area source a-Value (zonal) b-Value
CAL 4.1307 1.13
SWR 6.0750 1.58
ERZ 4.4646 1.48

Smoothed shallow seismicity

These point sources account for distributed seismicity not attributable to a specific feature. Occurrence rates for earthquakes M5.0-7.0 were derived for seven source zones (S1-7) with earthquakes <20 km depth (see Figure 2, Klein et al., 2001) across a 0.02° grid. Nodal planes are reverse focal mecahnisms with rotating strike and hypocentral depth fixed at 10 km. b-values are held constant across the grids, while a-values are adjusted according to the locally observed moment rates. Table 3 reports the GR-parameters, listing the a-value for the source zone (based on Table 3 in Klein et al., 2001). The tectonic region type is volcanic.

Source zone a-Value (zonal) b-Value
S1 5.2389 1.21
S2 3.1918 0.97
S3 4.1301 1.23
S4 2.7498 0.81
S5 4.2144 1.13
S6 3.7492 1.23
S7 4.8209 1.36

Deep shallow seismicity

These point sources are modelled the same as the shallow smoothed seismicity, varying only in their fixed hypocentral depth of 30 km. The six source groups (D1-6) are listed in Table 4 (based on Table 3 in Klein et al., 2001). The tectonic region type is deep seismicity.

Source zone a-Value (zonal) b-Value
D1 7.2195 1.71
D2 7.0389 2.03
D3 3.0028 0.93
D4 2.9083 0.90
D5 4.0666 1.07
D6 3.2977 0.91

Smoothed shallow seismicity, ramped

These point sources are modelled with the same focal mechanism and hypocentral depth as the smoothed shallow seismicity sources, but use only one source zone to resolve the GR b-value of 0.67. a-values are scaled not only by moment rate, but according to a ramping function that diminishes the modelled occurrence rates to the northwest; see the Appendix of Klein et al. (2001). The tectonic region type is volcanic.

Ground Motion Characterisation

As one of the oldest models implemented into the Global Hazard Mosaic, the Hawaii model relies on attenuation relationships developed in the 1990s. At the time, only a single model (Munson and Thurber, 1997) had been developed explicitly for Hawaii, and few accelerograms existed for testing. Thus, the model relies on a weighting of several GMPEs in order to account for trade offs between distance and magnitude in the relationships available at the time. The ground motion model uses different models for the different intensity metrics, and for different source groups. Here, source groups are divided partly by magnitude, rather than exclusively by tectonic region. Deep seismicity is modelled using intraslab equations.

A modified version of Munson and Thurber, 1997 was produced by the authors (Klein et al., 2001) for use in this model, and is documented therein.

Deep Seismicity Weight
Youngs et. al. 1997 1.0
Volcanic (M<7.0) Weight (PGA) Weight (SA T=0.2-0.3s) Weight (SA T>0.3s)
Boore et. al, 1997 0.25 0.33 0.5
Sadigh et. al, 1997 0.25 0.33 0.5
Munson and Thurber, 1997 0.25 0.34 -
Campbell, 1997 0.25 - -
Volcanic large (M>7.0) Weight (PGA) Weight (SA T=0.2-0.3s) Weight (SA T>0.3s)
Sadigh et. al, 1997 0.50 0.50 1.0
Munson and Thurber, 1997 0.50 0.50 -

Results

Hazard curves were computed with the OQ engine for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s. The computation was performed on a grid of 2081 sites (spaced at approximately 10 km) with reference soil conditions corresponding to a shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s.

The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.

References

Klein, F. W., Frankel, A. D., Mueller, C. S., Wesson, R. L., & Okubo, P. G. (2001). Seismic hazard in Hawaii: High rate of large earthquakes and probabilistic ground-motion maps. Bulletin of the Seismological Society of America, 91(3), 479-498.