Fred W. Klein

Deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of Kilauea

Dense microearthquake swarms occur in the upper south flank of Kilauea, providing multiplets composed of hundreds of events. The similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters. A simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically. Relocation of these events greatly improves the definition of the seismic image of the fault that generates them. Indeed, relative relocations define a plane dipping about 6° northward, although corresponding absolute locations are widely dispersed in the swarm. A composite focal mechanism, built from events providing a correct spatial sampling of the multiplet, also gives a well-constrained northward dip of about 5° to the near-horizontal plane. This technique thus collapses the clouds of hypocenters of single-event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies. We cannot conclude that all south flank earthquakes collapse to a single plane. There may locally be several planes, perhaps with different dips and depths throughout the south flank volume. The 6° northward-dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of Hawaii. This plane is probably an important feature that characterizes the basal slip layer below the upper south flank of Kilauea volcano. Differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane. The present work illustrates how high precision relative relocations of similar events in dense swarms, combined with the analysis of geodetic measurements, can help to describe deep fault plane geometry. Systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well-instrumented, highly seismic areas to provide reliable basic information, especially useful for understanding of earthquake generation processes.

Patterns of historical eruptions at Hawaiian volcanoes

Abstract Hawaiian eruptions are largely random phenomena displaying no periodicity; that is, future eruptions are relatively independent of the date of the last eruption. Several simultaneous processes probably govern eruption timing so that it appears random. I have performed statistical tests for nonrandomness on the repose times between eruptions and on the sequence of event types. Statistical differences that have physical consequences exist between large and small eruptions, summit and flank eruptions, and intrusive and extrusive events. Thus, large-volume eruptions tend to be followed by longer reposes as shallow magma reservoirs refill. On Kilauea, both summit eruptions and rapid intrusions tend to cluster at times associated with other physical events on the volcano. The longest recorded reposes of both Kilauea and Mauna Loa apparently are not random phenomena, for they appear to be associated with increased activity at the other volcano. Both eruption rates and volumes are consistent with a constant but alternating magma supply to the two volcanoes and an approximately five-fold larger magma reservoir at Mauna Loa than at Kilauea.

Seismic Hazard in Hawaii: High Rate of Large Earthquakes and Probabilistic Ground-Motion Maps

The seismic hazard and earthquake occurrence rates in Hawaii are locally as high as that near the most hazardous faults elsewhere in the United States. We have generated maps of peak ground acceleration (PGA) and spectral acceleration (SA) (at 0.2, 0.3 and 1.0 sec, 5% critical damping) at 2% and 10% exceedance probabilities in 50 years. The highest hazard is on the south side of Hawaii Island, as indicated by the M I 7.0, M S 7.2, and M I 7.9 earthquakes, which occurred there since 1868. Probabilistic values of horizontal PGA (2% in 50 years) on Hawaiis south coast exceed 1.75 g . Because some large earthquake aftershock zones and the geometry of flank blocks slipping on subhorizontal decollement faults are known, we use a combination of spatially uniform sources in active flank blocks and smoothed seismicity in other areas to model seismicity. Rates of earthquakes are derived from magnitude distributions of the modern (1959–1997) catalog of the Hawaiian Volcano Observatorys seismic network supplemented by the historic (1868–1959) catalog. Modern magnitudes are M L measured on a Wood-Anderson seismograph or M S. Historic magnitudes may add M L measured on a Milne-Shaw or Bosch-Omori seismograph or M I derived from calibrated areas of MM intensities. Active flank areas, which by far account for the highest hazard, are characterized by distributions with b slopes of about 1.0 below M 5.0 and about 0.6 above M 5.0. The kinked distribution means that large earthquake rates would be grossly underestimated by extrapolating small earthquake rates, and that longer catalogs are essential for estimating or verifying the rates of large earthquakes. Flank earthquakes thus follow a semicharacteristic model, which is a combination of background seismicity and an excess number of large earthquakes. Flank earthquakes are geometrically confined to rupture zones on the volcano flanks by barriers such as rift zones and the seaward edge of the volcano, which may be expressed by a magnitude distribution similar to that including characteristic earthquakes. The island chain northwest of Hawaii Island is seismically and volcanically much less active. We model its seismic hazard with a combination of a linearly decaying ramp fit to the cataloged seismicity and spatially smoothed seismicity with a smoothing half-width of 10 km. We use a combination of up to four attenuation relations for each map because for either PGA or SA, there is no single relation that represents ground motion for all distance and magnitude ranges. Great slumps and landslides visible on the ocean floor correspond to catastrophes with effective energy magnitudes M E above 8.0. A crude estimate of their frequency suggests that the probabilistic earthquake hazard is at least an order of magnitude higher for flank earthquakes than that from submarine slumps.

Case 23 nomination of precursory seismic quiescence as a significant precursor

ConclusionsSeveral cases of extremely strong quiescences have been investigated in great detail, and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity. Several additional cases of quantitatively measured quiescence have been documented. The method of measuring quiescence has progressed from using visual means to using a quantitative approach, and the understanding of the noise sources has significantly advanced during the last few years. Therefore I feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the List of Significant Precursors, although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process.

Relaxation of the south flank after the 7.2-magnitude Kalapana earthquake, Kilauea Volcano, Hawaii

An M = 7.2 earthquake on 29 November 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward several meters: a catastrophic release of compression of the south flank caused by earlier injections of magma into the adjacent segment of a rift zone. The focal mechanisms of the mainshock, the largest foreshock, and the largest aftershock suggest seaward movement of the upper block. The rate of aftershocks decreased in a familiar hyperbolic decay, reaching the pre-1975 rate of seismicity by the mid-1980s. Repeated rift-zone intrusions and eruptions after 1975, which occurred within 25 km of the summit area, compressed the adjacent portion of the south flank, apparently masking continued seaward displacement of the south flank. This is evident along a trilateration line that continued to extend, suggesting seaward displacement, immediately after the M = 7.2 earthquake, but then was compressed during a series of intrusions and eruptions that began in September 1977. Farther to the east, trilateration measurements show that the portion of the south flank above the aftershock zone, but beyond the area of compression caused by the rift-zone intrusions and eruptions, continued to move seaward at a decreasing rate until the mid-1980s, mimicking the decay in aftershock rate. Along the same portion of the south flank, the pattern of vertical surface displacements can be explained by continued seaward movement of the south flank and development of two eruptive fissures along the east rift zone, each of which extended from a depth of ∼3 km to the surface. The aftershock rate and continued seaward movement of the south flank are reminiscent of crustal response to other large earthquakes, such as the 1966 M = 6 Parkfield earthquake and the 1983 M = 6.5 Coalinga earthquake.

85.8 – The HYPOINVERSE2000 Earthquake Location Program

This chapter focuses on the HYPOINVERSE2000 Earthquake Location Program. The general features of HYPOINVERSE include command environment, file formats, crustal models, magnitudes, station gain history, station weighting, inversion, and output results. HYPOINVERSE2000 is command driven. Commands can be entered from the keyboard at the prompt or from a file. Models are in a flat Earth. Stations are at the surface but can have delays. Earthquake depths are thus below the local surface, but they are only an approximation if there is steep terrain like a conical volcano. Crustal models may either have homogeneous layers (with a model specified only by a table of velocities and depths), or have linear gradients within layers. Two different amplitude magnitudes based on a local magnitude formula from a variety of analog and digital, displacement or velocity stations may be computed for each event. Files with time-varying station gains and magnitude corrections are supported. Phases and stations may be individually weighted. Residual and distance weighting can suppress high-residual or distant stations. The program uses singular-value decomposition for the least-squares inversion that permits a variety of controls such as eigenvalue cutoff and damping. HYPOINVERSE2000 is written in Fortran 77 with (minor) extensions that compiles on UNIX (Sunos or Solaris), VMS (VAX or ALPHA), and PC OS2. The UNIX executable does not require that Fortran libraries be on the computer because it is compiled with the -Bstatic option. The UNIX executable is about 2 megabytes in size, which includes a station table of 4000 stations, earthquakes of 1000 phases, and 36 crustal models.

Dynamics of magma supply to Kīlauea volcano, Hawai‘i: integrating seismic, geodetic and eruption data

Abstract We focus on movement of magma beneath Kīlauea from the long summit eruption in 1967–1968 through the first historical sustained eruption on the east rift zone (Mauna Ulu 1969–1974), ending with the occurrence of a magnitude 7.2 earthquake beneath Kīlaueas eastern south flank. Magma from the Hawai‘iian hot spot continuously moves upward to summit storage and drives seaward spreading of Kīlaueas south flank on a 10–12 km deep décollement. Spreading creates dilation in Kīlaueas rift zones and provides room to store magma at depths extending to the décollement surface. During the period of study three types of eruptions – normal (short-lived), episodic and sustained – and three types of intrusions – traditional (summit to rift), inflationary and slow – are classified. Rates of sustained eruption are governed by the geometry of the magmatic plumbing. Swarms of earthquakes beneath the south flank signal increased pressure from magma entering Kīlaueas adjacent rift zone. Magma supply rates are obtained by combining the volume of magma transferred to sites of eruption or intrusion with the volume opened by seaward spreading over the same increment of time. In our interpretation the varying character of eruptions and intrusions requires a gradual increase in magma supply rate throughout the period augmented by incremental increases in spreading rate. The three types of eruptions result from different combinations of magma supply and spreading rate.

Lithospheric flexure under the Hawaiian volcanic load: internal stresses and a broken plate revealed by earthquakes

Several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilaueas deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.

New earthquake catalog reexamines Hawaii's seismic history

On April 2,1868, an earthquake of magnitude 7.9 occurred beneath the southern part of the island of Hawaii. The quake, which was felt throughout all of the Hawaiian Islands, had a Modified Mercalli (MM) intensity of XII near its source.The destruction caused by a quake that large is nearly complete. A landslide triggered by the quake buried a small village, killing 31 people, and a tsunami that swept over coastal settlements added to the death toll. We know as much as we do about this and other early earthquakes thanks to detailed records kept by Hawaiian missionaries, including the remarkable diary maintained by the Lyman family that documented every earthquake felt at their home in Hilo between 1833 and 1917 [Wyss et al., 1992].Our analysis of these and other historical records indicates that Hawaii was at least as intensely seismic in the 19th century and first half of the 20th century as in its more recent past, with 26 M ≥6.0 earthquakes occurring from 1823 to 1903 and 20 M ≥6.0 earthquakes from 1904 to 1959. Just five M ≥6.0 earthquakes occurred from 1960 to 1999. The potential damage caused by a repeat of some of the larger historic events could be catastrophic today