Paleoseismic Analysis of the South Flank of Kilauea Volcano, Hawaii

Eric Cannon

1. Summary

A detailed paleoseismic analysis of the Hilina Fault System (HFS) on the south flank of Kilauea Volcano, Hawaii, will improve geologic hazard assessment in the region. Geologic hazards of the south flank region include large seismic events, volcanic activity, and tsunami waves resulting from seismic or volcanic events. This paleoseismic study focuses on paleoseismology correlating historical surface faulting with previous seismic events. The initial investigation will focus on fault displacement analysis of the 1975 Kalapana earthquake. One product of this study will be a detailed fault rupture map of the south flank, consisting of rupture traces and displacement measurements associated with the 1975 Kalapana earthquake. Further paleoseismic investigations will establish recurrence intervals for major south flank earthquakes, map and quantify earthquake displacements previous to the 1975 Kalapana event, and estimate displacement rates for the south flank region.

2. Motivation

Presently two active volcanoes exist on Hawaii, Mauna Loa and Kilauea. Major geologic features of the south flank of Kilauea Volcano include Kilauea caldera, and the Southwest and East Rift Zones (Figure 1). A decollement surface (Figure 3) is interpreted at depths of 5-10 km, representing an interface between the Pacific oceanic lithosphere and Hawaiian volcanic edifice (Ando, 1979). The south flank region exhibits concentrated active seismicity and volcanic activity. South flank geologic hazards include seismic and volcanic events, associated tsunamis, and mass movements. Two major normal fault systems, the Koae and Hilina Faults Systems (HFS), trend approximately northeast-southwest across the south flank. Significant earthquakes have occurred on the south flank in 1823, 1868, 1975, and 1989. Only two historic earthquakes produced displacement along the HFS (Figure 1), 1868 M 7.9 Kau (Clague & Denlinger, 1993) and 1975 M 7.2 Kalapana earthquakes (Tilling et al., 1975; Lipman et al., 1985). On November 29, 1975, the M 7.2 Kalapana earthquake produced maximum south flank displacements of 8 meters seaward and 3 meters vertical subsidence (Lipman et al., 1985). Displacement of the south flank locally generated a 14 meter high tsunami detected in the western Pacific, Alaska, and California. Total damages in Hawaii from the earthquake and resulting tsunami exceeded $ 4 million (Tilling et al., 1975).

Figure 1. Location map of south flank of Kilauea Volcano, Hawaii. Black triangles represent earthquake epicenters. Line of section plotted for Figure 4.

Earthquakes may trigger mass movements of coastal areas on oceanic volcanic islands. Hummocky terrain offshore of the Hawaiian islands (Figure 2) has been interpreted as catastrophic mass movement landslides of the volcanic edifice (Denlinger & Okubo, 1995). Normal faults, such as the HFS, may represent the surface expression of mass movement slump headscarps.

Figure 2. Several submarine landslides have been identified offshore of Hawaii (modified from Moore et al., 1995)

To begin a paleoseismic analysis of the south flank, this project will focus on surface deformation associated with the 1975 Kalapana earthquake. The 1975 earthquake is the only major Hawaiian historical earthquake where geodetic surveys were conducted before and after the earthquake. A detailed rupture and fault displacement map of the Kalapana earthquake will be constructed, as no detailed map has yet been produced. Spatial variability of magnitude and orientation of offsets will be analyzed from the fault displacement map to better understand the kinematics of the south flank. In addition to the Kalapana event, earthquake displacements prior to 1975 will be analyzed and dated. Recurrence intervals of south flank earthquakes will be calculated.

3. Previous Research

Geodetic surveys of the south flank consist of trilateration and precise leveling line data, and GPS campaigns. Hawaii Volcano Observatory (HVO) scientists resurveyed precise leveling lines and trilateration networks in early 1976 following the 1975 Kalapana earthquake (Lipman et al., 1985). Strain accumulation on the HFS was noted prior to the Kalapana earthquake (Swanson et al., 1976) from geodetic measurements. This strain accumulation produced contraction of the south flank which possibly triggered the 1975 Kalapana earthquake (Swanson et al., 1976). Owen et al. (1995) modeled the south flank with GPS survey data collected from 1992-1996. During these 5 years, the south flank has not displayed a significant strain accumulation (Owen et al.,1995), suggesting that the south flank has not post-seismically recovered from the 1975 Kalapana earthquake. Owen et al. (1995) associates 1990's deformation with aseismic slip of the volcanic edifice.

Kinematics of the south flank can be addressed by modeling of geodetic data. A controversy exists regarding the depth of faulting in the HFS; faulting could be either shallow or deep. In addition to surface displacement along the HFS, the 1975 Kalapana earthquake hypocenter occurred at 10 km depth and produced a thrust focal mechanism (southeast transport direction) on a sub-horizontal fault plane dipping ~6 degrees to the north (Ando, 1979). The 1975 Kalapana earthquake is interpreted as a detachment event occurring along the interface between the Pacific oceanic lithosphere and Hawaiian volcanic edifice (see Lipman et al., 1985).

Inferring the HFS as shallow faults (Hill & Zucca, 1987), normal faults with dips of 60-70 at the surface shallow into listric normal faults at depths of 2-3 km (Figure 3a). Headscarps of the HFS represent shallow slump blocks, and surface faults do not directly link with the deeper decollement surface. Listric faults would produce a northward back-rotation of hangingwall blocks in the HFS. Riley (1996) concludes from paleomagnetic analysis that Puu Kapukapu has been down-faulted and northward back-rotated on a 5 km deep listric normal fault with respect to the Hilina Pali. Seismicity may trigger landslides on shallow HFS normal faults.

Figure 3a. HFS interpreted with shallow listric normal faults (modified from Hill & Zucca, 1987). Figure 3b. HFS connects to decollement surface at depth (modified from Lipman et al., 1985)

The HFS may be interpreted as surface normal faults descending to 5-10 km depths and forming a splay with the decollement surface (Figure 3b). Seismic slip on the decollement may induce surface displacements on the HFS. P-wave tomographic studies indicate an anomalous velocity gradient at depth in the HFS region (Okubo et al., 1997). They also identify a concentration of microseismicity at the proposed splay junction of the HFS and decollement faults (Figure 4). These two conclusions provide evidence for the linkage between HFS surface normal faults and the decollement.

Figure 4. Cross-section interpretation of HFS deep normal faults from P-wave tomographic studies (from Okubo et al., 1997). Line of section on Figure 1.

HVO scientists produced summary maps of 1975 Kalapana earthquake contoured vertical and horizontal displacements (Tilling et al., 1975) on a 1:500 000 scale map. These maps are based on geodetic station displacements, not data from individual total displacement measurements along the earthquake rupture of the HFS. Kellogg & Chadwick (1985) measured fault displacements in the western HFS by traversing fault scarps (Figure 5). Their measurements indicate varied magnitude and direction of total fault displacements from the Kalapana earthquake.

Figure 5. Displacement map for western HFS from 1975 Kalapana earthquake (Kellogg & Chadwick, 1985).

Lava flows originating from Kilauea caldera and rift zones flow over HFS fault scarps. Stratigraphic and 14C methods provide dates for these flows. Stratigraphy of south flank lava flows has been constructed back to approximately 50-100 ka (Easton, 1987; Holcomb et al., 1987), relative to seven age-dated major ash members. Estimates on the age of the HFS vary, from 23 ka (Pahala Ash) on Puu Kapukapu (Easton, 1978), to 35.8 ka (Pohakaa Ash) on Puu Kapukapu and Hilina Pali (Riley, 1996). Organic material and charcoal originating from plants such as tree ferns and ohia trees can be dated using 14C dating techniques (see Wolfe & Morris, 1996). Assuming these plants were killed by an advancing lava flow, 14C dates can provide an estimated age of the lava flow.

4. Methods

Preliminary field investigations of the HFS in June 1995 and March 1998 identified practical field techniques required to achieve the goals of this project. A combination of office research and fieldwork will be applied in this project.

One goal of this project is to produce a detailed fault displacement map of the 1975 Kalapana earthquake. Aerial photographs from 1965 (1:24 000 scale) will be scanned into a computer system and used to identify fault ruptures prior to the 1975 Kalapana earthquake. Several series of aerial photos (1:12 000 - 1985, 1:5 000 & 1:10 000 - 1975, 1:24 000 orthophotoquad-1977) clearly display Kalapana earthquake displacements in pahoehoe and aa lava flows. These post-earthquake aerial photographs will be interpreted and used to produce an initial Kalapana earthquake trace map.

Field mapping of the Kalapana displacements during Summer 1998 will utilize GPS surveying equipment to produce a detailed fault displacement map. In the east-central region of the HFS, pahoehoe lava flows and proximity to the Chain of Craters Road will allow the use of GPS Real-Time Kinematic (RTK) survey-grade technology. Surface features can be surveyed with an accuracy of ~1 cm, thus piercing points and surface rupture geometry can be mapped in great detail. In remote regions of the field area, where RTK technology will be difficult to use or create a safety hazard, aerial photos will be used to identify the location of fault displacements, and a mapping-grade GPS receiver (1-5 meter location accuracy) will be used to map locations of fault displacements. Displacements will be measured with nylon tape measures, and attitude of piercing points will be measured with a compass.

As part of the paleoseismic analysis of the HFS, cross-cutting relationships in the lava flows can be used to determine displacements and maximum ages of displacement for previous earthquake events. Lava flows with ages previously determined will be visited and examined for earthquake displacement. If an earthquake fissure displaces a dated lava flow, a maximum age can be associated with the earthquake event. Lava flow outcrops with organic matter or charcoal will be sampled for later 14 C dating, or possibly uranium-series dating.

5.Discussion of Possible Results

Geologic hazard assessment of the south flank region will benefit from this paleoseismic analysis. This project calls for the production of the first ever detailed fault displacement map of the 1975 Kalapana earthquake. Detailed fieldwork will identify displacements from other earthquake events, such as 1868 M 7.9 Kau earthquake. Recurrence intervals for major seismic events will be estimated. Estimates of the age of the HFS and amount of extension across the HFS will be calculated. Displacement data can be used to better constrain boundary conditions in kinematic models of the HFS, and aid in distinguishing whether the HFS is a deep or shallow fault system.

6. References

Ando, M., 1979, The Hawaii earthquake of November 29, 1975: Low dip angle faulting due to forceful injection of magma: J. Geophys. Res., v. 84, p. 7616-7626.

Clague, D. A., and Denlinger, R. P., 1993, The M 7.9 1868 earthquake: Hawaii's active landslides [abs.], Eos, Transactions, American Geophysical Union supp., v. 74 (no. 43), p. 635.

Denlinger, R. P., and Okubo, P., 1995, Structure of the mobile south flank of Kilauea Volcano, Hawaii: J. Geophys. Res., v. 100, p. 24499-24507.

Easton, R. M., 1978, The stratigraphy and petrology of the Hilina Formation: the oldest exposed lavas of Kilauea Volcano, Hawaii [M.S. thesis]: University of Hawaii.

Easton, R. M., 1987, Stratigraphy of Kilauea Volcano. In: Decker, R. W., Wright, T. L., and Stauffer, P. H., 1987,Volcanism in Hawaii, v. 1, U. S. Geol. Surv. Prof. Pap. 1350, p. 243-260.

Hill, D. P., and Zucca, J. J., 1987, Geophysical constraints on the structure of Kilauea and Mauna Loa Volcanoes and some implications for seismomagmatic processes: U. S. Geol. Surv. Prof. Pap., v. 1350, p. 903-917.

Holcomb, R. T., 1987, Eruptive History And Long-Term Behavior Of Kilauea Volcano: U. S. Geol. Surv. Prof. Pap., v. 1350, p. 261-350.

Kellogg, J. N., and Chadwick, W., 1987, Neotectonic study of the Hilina Fault System, Kilauea, Hawaii: Geol. Soc. Am. Abstr. w. Program., v. 19, no. 6., p. 394.

Lipman, P. W., Lockwood, J. P., Okamura, R. T., Swanson, D. A., and Yamashita, K. M., 1985, Ground Deformation Associated With The 1975 Magnitude-7.2 Earthquake And Resulting Changes In Activity Of Kilauea Volcano 1975-1977, Hawaii: U. S. Geol. Surv. Prof. Pap., v. 1276, p. 1-45.

Moore, J. G., Bryan, W. B., Beeson, M. H. and Normark, W. R., 1995, Giant blocks in the South Kona landslide, Hawaii: Geology, v. 23, p. 125-128.

Okubo, P. G., Benz, H. M., and Chouet, B. A., 1997, Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii: Geology, v. 25, n. 10, p. 867-870.

Owen, S., Segall, P., Freymueller, J., Miklius, A., Denlinger, R., Arnadottir, T., Sako, M., and Bürgmann, R., 1995, Rapid deformation of the south flank of Kilauea Volcano, Hawaii: Science, v. 267, p. 1328-1332.

Riley, C. 1996, A Paleomagnetic Study of Movement in the Hilina Fault System, South Flank of Kilauea Volcano, Hawaii [M. S. thesis]: Michigan Technology University.

Swanson, D. A., Duffield, W. A., and Fiske, R. S., 1976, Displacement of the south flank of Kilauea Volcano: the result of forceful intrusion of magma into the rift zones: U. S. Geol. Surv. Prof. Pap., v. 963, p. 1-37.

Tilling, R. I., Koyanagi, R. Y., Lipman, P. W., Lockwood, J. P., Moore, J. G., and Swanson, D.W., 1976, Earthquake and Related Catastrophic Events Island of Hawaii, November 29, 1975: A preliminary report: U. S. Geol. Surv. Circ. 740., p. 1-33.