Do flexural stresses explain the mantle fault zone beneath Kilauea volcano? (original) (raw)
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Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes
Nature, 2008
Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate 1,2 . Despite the apparent simplicity of the parent processemission of magma onto the oceanic crust-the resulting edifices display some topographic complexity . Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown 6,7 . Here we use seismological investigations and finiteelement mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities . Further studies are needed to determine whether such processes occur in other active intraplate volcanoes.
LETTERS Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes
Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate 1,2 . Despite the apparent simplicity of the parent processemission of magma onto the oceanic crust-the resulting edifices display some topographic complexity . Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown 6,7 . Here we use seismological investigations and finiteelement mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities . Further studies are needed to determine whether such processes occur in other active intraplate volcanoes.
An estimate of the absolute stress tensor in Kaoiki, Hawaii
Journal of Geophysical Research, 1992
The stress tensor orientation was calculated by inversion of 81 fault plane solutions of M = 3.5 +_ 0.6 earthquakes located in an area 6 by 16 km at depths of 7 +_ 2 km. This crustal volume is situated on a straight line between the summits of the active volcanoes Kilauea and Mauna Loa. The orientation of the greatest principal stress was found to be near horizontal and in the line connecting the two volcanoes. This is further evidence supporting the model that magmatic expansion within the feeding conduits of these volcanoes is the source of stress that causes earthquakes in southern Hawaii. These earthquakes are tectonic earthquakes in the sense that they occur in a brittle elastic crust at distances of a few to several tens of kilometers from the volcanoes, and that they are not directly associated with the opening of cracks by intrusions. We propose that this model leads to the corollary that the shear stresses (x) responsible for earthquake failure in the shallow Hawaiian crust are approximately 3 +_ 2 MPa, and that the pore pressure of ground-water (p) in the hypocentral volume must be under near lithostafic pressure. This result is obtained by arguing that the greatest principal stress (o•) is equal to the magma pressure in the volcanic feeder pipe, but cannot exceed the least principal stress (ø3) by more than the tensile strength of the crust, because otherwise hydrofracture would occur, opening a crack against the least principal stress. Given the difference between the greatest and least principal stress, the fact that the overburden at the 7 km hypocentral depth equals the intermediate principal stress and the ratio R = (ol -•2 )/( ol -•3)= 0.4, which is obtained in the inversion of fault plane solutions, we estimate that ol = 202 MPa, •2 = 200 MPa, •3 = 196 MPa, x = 3 MPa, and o n = 199 MPa, with uncertainties on the order of several MPa. It follows that for any coefficients of friction larger than 0.15, the pore fluid pressure necessary for faulting on the observed fault planes has to be larger than 90% of the lithostafic pressure. These considerations suggest that many eanhquakes represent fault ruptures under low ambient shear stresses in the order of the average observed stress drop of 3 MPa. INTRODUCFION The Hawaiian islands have a high seismicity rate with an average return time for earthquakes M > 6 of 5.5 years [Wyss and Koyanagi, 1991]. The source of stress that causes these earthquakes is not thought to be connected with the movements of the Pacific plate because the plate boundaries are remote from Hawaii. Instead the stress is due to the volcanic activity, with the highest seismicity rate in southern Hawaii at and near Kilauea and Mauna Loa [e.g., Klein et al., 1987; Koyanagi et al., 1988]. We are aware of four different ways in which the active volcanoes can cause earthquakes: (1) volcanic earthquakes associated directly with the opening of cracks by magmatic intrusions, (2) tectonic earthquakes due to the stress exerted on the crust by intrusions, (3) faulting due to the edifice load on the oceanic crust, and (4) landsliding. In this paper we attempt to estimate the absolute values of the stress tensor for the type 2 earthquakes mentioned above. Wood [1914] used the term "tectonic" to distinguish the earthquakes which occur at several kilometers to several tens of kilometers distance from the "volcanic" seismic activity of thousands of earthquakes which occur in swarms along cracks that are opened by magma intrusions. Geodetic measurements show that the crust surrounding the volcano summits and the rift zones is compressed during intrusions [e.g., Swanson et al., 1976; Dvorak et al., 1983, 1986; Dzurisin et al., 1984]. In some cases aftershock sequences without a mainshock are induced in Kilauea's south flank by the Paper number 91JB01455. 0148-0227/92/91J B-01455 $ 05.00 intrusions. For several weeks during and following an intrusion in one of Kilauea's rifts the adjacent crustal volumes at several to 10 km distance in the south flank produce seismicity that has all the attributes of an aftershock sequence [e.g., Koyanagi et al., 1972; Wyss and Kisslinger, 1989]. Thus there is no doubt that in southern Hawaii stress is introduced into the crust by hydraulic pumping much as in a rock mechanics laboratory, and that brittle failure of the crust ultimately leads to earthquakes, some of which can reach magnitude 8 [Wyss, 1988]. The bending of the crust and lithosphere due to the load of the volcanic edifice that is deposited upon the plate as it passes over the Hawaiian plume may also contribute to the seismicity of Hawaii [Johnson and Koyanagi, 1986]. However, based on our surveys of fault plane solutions we conclude that few normal faults with approximate 45 ø dipping planes are observed, and hence this activity is probably playing a minor role. Large landslides have occurred on all Haiian islands [e.g., Lipman et al., 1988; Moore et al., 1989], a landslide type normal fault has been activated in a large earthquake [Tilling et al., 1976], and there is a question of how much landsliding activity may have occurred in that earthquake [Eissler and Kanamori, 1987, 1988; Wyss and Kovach, 1988]. However, landslide events occur on the fringes of the island and they are relatively rare. We will constrain our observations to an area away from the outer slopes of the island. The area of study is the Kaoiki area located between the volcano summits of Kilauea and Mauna Loa (Figure 1). After Kilauea's south flank this is the most active area for tectonic earthquakes in Hawaii. Magnitude 6 _.+ 0.5 mainshocks occur in this crustal volume at approximately regular intervals of 10.4 + 1.5 years [Wyss, 1986]. Based on inversions of 238 focal mechanisms we found that the stress tensor directions were different in the NW and SE of this 10 km radius area, and that they also were different above and below 9 km depth [Wyss et al., 1992]. The crustal volume for which we have the most 4763 4764 WYSS ET AL.: ABSOLLrrE STRESS TENSOR IN KAOIKI, HAWAII ,• LOA /! , O '7/ 02 ß 01 291-298, 1989.
Journal of Geophysical Research: Solid Earth, 1979
The mechanism of the Hawaii earthquake of November 29, 1975 (Ms = 7.1), which took place on the south flank of Kilauea Volcano, is discussed on the basis of a comprehensive set of body wave and surface wave data, the aftershock distribution, and tsunami and crustal deformation data. The aftershock distribution defines a gently dipping plane at about 10-km depth beneath the south flank of Kilauea. This suggests that the shallowly dipping P wave nodal plane fits the fault of the Hawaii earthquake better than the nodal plane that has a nearly vertical dip angle. The fault length is fixed well by the aftershock distribution, which is also consistent with the tsunami and crustal deformation data. The fault width which is obtained from tsunami and crustal deformation data is, however, significantly greater than that obtained from the aftershock distribution. This discrepancy implies that about half of the main shock fault plane was not associated with aftershock activity. The source parameters are strike N70øE; dip angle 20øSSE; fault length 40 km; seismic moment 1.8 x l0 27 dyne-cm; fault width 20-30 km; fault movement is pure normal dip slip of 3.7-5.5 m, and stress drop is 43-93 bars. Results of geodetic surveys throughout the twentieth century and a history of volcanic activity on Kilauea imply that a north-south compression due to magma injected into rift zones may have steadily increased on the south flank of Kilauea since the 1868 earthquake, an event comparable to the 1975 shock. This compressional stress was possibly released by the 1975 Hawaii earthquake. The long-term eruptive activity of Kilauea may be affected by large earthquakes like the 1868 and 1975 events and may also have a similar 100-yr recurrence interval. INTRODUCTION Kilauea Volcano on the island of Hawaii currently erupts at an average rate of 0.1 km3/yr [Swanson, 1972; Shaw, 1973], a volume approximately equal to all the volcanoes in Japan. Straining caused by intrusions into magma chambers and rift zones is larger than in any other tectonic area. During the last 80 yr, the horizontal strain on the south flank of Kilauea has amounted to 2 x 10-4, SO that the strain rate is 5 x 10-6/yr. This strain rate is 1 order of magnitude higher than the average secular rates in California [Prescott et al., 1979] and Japan [Nakane, 1973]. Kilauea Volcano thus is remarkable in terms of strain accumulation. Recently, volcanologists have studied this volcano with a view toward earthquake prediction, because eruptions have significantly increased and the horizontal strains accumulated on the southern flank may have reached a critical level [Swanson et al., 1976]. Swanson et al. anticipated a large earthquake similar to the 1868 event with large crustal deformation and tsunami on the southern coast [Hitchcock, 1912; Wood, 1914]. On November 29, 1975, a large earthquake (Ms-7.1) struck the southern part of the island of Hawaii after a sequence of foreshocks. The focal coordinate, depth, and origin time were subsequently reported at 19ø20'N, 155ø02'W, 5 kin, and 1447:40.4 UT, respectively, by the U.S. Geological Survey (USGS). Earthquake phenomena associated with this earthquake are quite similar to those of the 1868 earthquake. During the 1975 earthquake, the south coast of Kilauea subsided, an extensive tsunami occurred, Kilauea erupted a small volume of lava, and the summit area of the volcano collapsed [Tilling et al.,
Journal of Geophysical Research, 1994
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 theft 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 ø 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 ø 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 ø 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. introduction Kilauea Volcano has many geological features of major interest. Indeed, Kilauea Volcano, built on the southeast flank of Mauna Loa Volcano, exhibits beside the caldera, two large rift zones delimiting the south flank, which slides seaward. Other volcanoes (Piton de la Fournaise, Etna, Mount St. Helens) present more or less similar sliding structures. But only at Kilauea Volcano is there almost continuous seismic and eruptive activity, as well as a high horizontal strain rate, related to this movement. Tectonics and seismicity of the south flank of Kilauea have been extensively studied [Swanson et al.Paper number 94JB00577. 0148-0227/94/94JB-00577505.00 at the base of the volcanic pile on the oceanic crust at a depth of about 9 km to explain the seaward movement of the south flank. This fault plane has been inferred from geodetic measurements [Swanson et al., 1976; Arnadottir et al., 1991], from focal mechanisms, surface wave analysis and tsunami records after the Kalapana (1975, M s = 7.2) earthquake [Ando, 1979] but never directly de-termined from simple earthquake hypocenter locations. Indeed earthquake locations are distributed in ellipsoidal volumes, whose major axis is roughly vertical, ranging from 5-to 10-kin depth [Klein et al., 1987]. This distribution does not define a fault plane [Arnadottir et al., 1991 ]. Crosson and Endo [1982] hypothesize that most of the vertical scatter was due to location errors and supported the idea of a sub-horizontal fault plane. Klein et al. [1987] and Thurber and Gripp [1988] show hypocentral cross-sections and use the base of the seismic zone to define the decollement plane. The use of microearthquake. focal mechanisms leads to numerous partial results, but also different interpretations [Crosson and Endo, 1982; Thurber and Gripp, 1988; Bryan and Johnson, 1991; Bryan, 1992]. Added to the 15,375 15,376 GOT ET AL.: DEEP FAULT PLANE GEO•Y ß co
Ground ruptures of the 1974 and 1983 Kaoiki earthquakes, Mauna Loa volcano, Hawaii
Journal of Geophysical …, 1992
The November 30, 1974, Mt• = 5.5 and November 16, 1983, Mt• = 6.6 earthquakes generated left-stepping, en echelon ground cracks within the Kaoiki seismic zone, on the southeast flank of Mauna Loa volcano, Hawaii. The general trend of the ruptures, N48ø-55øE, parallels a nodal plane of the main shocks' focal mechanisms. The ruptures themselves consist of short, predominantly extension cracks, which are up to 20 m long and strike roughly E-W, 300-50 ø clockwise from the overall trend of the zones. Some of the cracks are linked by secondary fractures and rubble breccia to form left-stepping crack arrays, which are themselves linked to form longer en echelon systems of ground rupture. Geologic maps and field observations indicate that these features emerge from an underlying strike-slip fault, and they form a "fracture-process zone" above its tip. The maximum displacement measured across cracks in the 1983 rupture zone is 0.5 m. Trilateration data, however, suggests that the overall shear displacement was about 1.5 m at depth. Elastic solutions indicate that a region of significant tensile stress can exist above buried strike-slip faults. We suggest that these stresses generated the extensional ground cracks and that shear displacements were transmitted to the Earth's surface by subsequent growth and linkage of these cracks into the observed arrays. We infer that the crack arrays accommodate increased displacement with depth and they merge downward into the "parent" strike-slip fault at an estimated 1-2 km depth, where strike-slip displacement was probably more or less continuous along the -•7 km length of the rupture. In the Kaoiki region, only three major ground ruptures traverse a series of basaltic lava flows that date back 1500 years. This suggests that the recent -• 10-year periodicity of moderate-magnitude Kaoiki strike-slip events may not have extended far into the past. The tectonic significance of strike-slip faulting on Mauna Loa volcano remains enigmatic. Allen et al., 1991]. Low-angle thrust faulting at depths of 6 to 12 km [e.g., Bryan and Johnson, 1991], gravity-controlled normal faulting [e.g., Moore and Krivoy, 1964; Moore eta!., 1989], and magma migration in rift-zone dikes [e.g., Swanson eta!., 1976] dominate the tectonic interpretation of Hawaiian volcanoes and their unstable seaward-facing flanks. The 1983 and 1974 Kaoiki earthquake focal mechanisms, however,
Geophysical Journal International, 2020
SUMMARY The May 2018 activity at Kīlauea Volcano, Hawaii involved magma transport and dyke intrusion along the East Rift Zone (ERZ) and nucleation of the 4 May 2018 M 6.9 earthquake along the basal décollement of Kīlauea's mobile south flank. Combined Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) measurements captured the deformation sequence associated with the dyke intrusion, main shock and eruption episode along the ERZ. The earthquake was encouraged by static stress changes from the preceding magma reservoir inflation, ERZ expansion and fault creep on the décollement downdip of the rupture. Slip models derived from the inversion of GPS displacements indicate peak coseismic slip of 2–3 m. Our model analyses, including of the pre-May 2018 deformation, suggest that prior to this event there was no slip on the section of the décollement that ruptured in the earthquake. The observed magma inflation, rapid fault creep on the décollement and ...
Journal of Geophysical Research, 1998
In January 1983, a dike intrusion/fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16-km segment of Kilauea' s Middle East Rift Zone. We searched the Hawaiian Volcano Observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation. Over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation. Some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm, consistent with generation near the propagating dike tip, while others were active for several days. The two multiplets nearest the origin of the seismic swarm include events from the preceding days and months. Most multiplets span only 50 to 100 m following relocation, are located at about 3 to 4 km depth, and appear to deepen downrift. The catalog depths of those earthquakes in multiplets and those not in multiplets are similar, suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface. By analogy with a mechanical model used to explain a similar clustering of background seismicity in the Upper East Rift in 1991, we infer that the earthquakes are generated in regions of high stress concentration immediately above Kilauea's deforming deep rift body. This conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1.
Geology, 2014
An anomalous body with low Vp (compressional wave velocity), low Vs (shear wave velocity), and high Vp/Vs anomalies is observed at 8-11 km depth beneath the upper east rift zone of Kilauea volcano in Hawaii by simultaneous inversion of seismic velocity structure and earthquake locations. We interpret this body to be a crustal magma reservoir beneath the volcanic pile, similar to those widely recognized beneath mid-ocean ridge volcanoes. Combined seismic velocity and petrophysical models suggest the presence of 10% melt in a cumulate magma mush. This reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 M7.2 Kalapana earthquake.