High stress drop events in the Victoria, Baja California earthquake swarm of 1978 March

Munguía, Luis; Brune, James N.

doi:10.1111/j.1365-246x.1984.tb01919.x

Cited by 25 publications

(12 citation statements)

References 28 publications

(33 reference statements)

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“…In addition to the RANM strong-motion data, weak-and strong-motion records collected during the occurrence of the 1978 Victoria earthquake swarm were included in our shear-wave splitting analysis. This earthquake series was studied in detail by MUNGUI´A and BRUNE (1984). The swarm activity began on March 10, 1978 and continued for about 12 days, with some earthquakes reaching local magnitudes as high as 4.8.…”

Section: Instruments and Datamentioning

confidence: 99%

“…Each recorder was combined with velocity sensors of 5-or 1-sec natural periods. The seismic signals detected by these instruments were sampled at 100 sps on each channel (MUNGUI´A and BRUNE, 1984). Although such network recorded many events with magnitudes between 2.0 and 4.1, only records with reliable signal-to-noise ratios were included in the study.…”

Section: Instruments and Datamentioning

confidence: 99%

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Seismic Anisotropy Observations in the Mexicali Valley, Baja California, M�xico

González

Munguía

2003

Pure and Applied Geophysics

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A study of seismic anisotropy was performed using data from earthquakes of the Mexicali Valley. The investigated region encompasses the Cerro Prieto Geothermal Field (CPGF), one of the most important fields in the world. The results showed that at most of our stations the average polarization directions of the fast S waves range from N14°W to N17°E. A N-S polarization direction was obtained for the whole area by averaging the polarization directions from all stations used. In terms of the EDA hypothesis, this average trend agrees with the postulated state of stress for southern California, and with fault plane solutions for events of the Mexicali Valley. Notorious deviations from the N-S global trend were found southeast of the CPGF, with polarization trends between N25°E and N67°E, and in the geothermal field, with polarization directions between N7°W and N14°W. The polarization results for these zones indicated stress conditions that are different from the more regional stress pattern.The delay times that were measured between the fast and slow shear waves reached values of up to 0.6 sec, with a mean value of 0.35 sec. Consistent with our polarization results, the larger delay times (0.2-0.6 sec) were found in the CPGF. Smaller or null values were observed at the periphery of the study area. No temporal trends in the delay times were apparent, as shown by data from the two stations that recorded the larger number of events.Overall, we conclude that the splitting effects of this study result from a shallow anisotropy volume. The splitting results are thus interpreted as caused by the preferred orientation of vertical fluid-filled microcracks aligned in a direction that is parallel to the regional stress field. The stronger splitting effects that were observed in the area of the CPGF were found consistent with the geothermal reservoir that is embedded in the sedimentary cover of the zone, at depths of 1 to 4-5 km from the surface. We thus believe that such marked splitting effects have a direct relation with the reservoir of the CPGF.

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Section: Instruments and Datamentioning

confidence: 99%

Section: Instruments and Datamentioning

confidence: 99%

Seismic Anisotropy Observations in the Mexicali Valley, Baja California, M�xico

González

Munguía

2003

Pure and Applied Geophysics

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“…In addition, stress drops on the order of hundreds of MPa appear to be rare but have been observed. Munguia and Brune (1984) calculated stress drops in excess of 200 MPa for events in the 1978 Victoria, Baja California, earthquake swarm. Kanamori et al (1990Kanamori et al ( , 1993 estimated stress drops for a small earthquake in Pasadena, California, between 30 and 200 MPa.…”

Section: Evidences Of High Stress Drop For Small Eventsmentioning

confidence: 99%

Stress Drop during Earthquakes: Effect of Fault Roughness Scaling

Candela

Renard

Bouchon

et al. 2011

Bulletin of the Seismological Society of America

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We propose that a controlling parameter of static stress drop during an earthquake is related to the scaling properties of the fault-surface topography. Using high resolution laser distance meters, we have accurately measured the roughness scaling properties of two fault surfaces in different geological settings (the French Alps and Nevada). The data show that fault-surface topography is scale dependent and may be accurately described by a self-affine geometry with a slight anisotropy characterized by two extreme roughness exponents (H R ), H jj 0:6 in the direction of slip and H ⊥ 0:8 perpendicular to slip.Disregarding plastic processes like rock fragmentation and focusing on elastic deformation of the topography, which is the dominant mode at large scales, the stress drop is proportional to the deformation, which is a spatial derivative of the slip. The evolution of stress-drop fluctuations on the fault plane can be derived directly from the self-affine property of the fault surface, with the length scale (λ) as std Δσ λ ∝ λ H R 1 . Assuming no characteristic length scale in fault roughness and a rupture cascade model, we show that as the rupture grows, the average stress drop, and its variability should decrease with increasing source dimension. That is for the average stress drop Δσr ∝ r H R 1 , where r is the radius of a circular rupture. This result is a direct consequence of the elastic squeeze of fault asperities that induces the largest spatial fluctuations of the shear strength before and after the earthquake at local (small) scales with peculiar spatial correlations.

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“…Therefore, it is necessary to elaborate a methodology that allows minimizing the errors in the fitting. Different authors have proposed various methodologies: a simple choice of the better fitting for both asymptotes (Munguía & Brune 1984); the constructing of a low‐frequency line at the level of 66–70 per cent of the maximum peaks of the spectrum and picking of fc at the intersection with the last oscillation at low‐frequency level (Aptekman et al 1989; Zobin & Havskov 1995) or a spectra fitting using model reconstructions (Abercrombie 1995). These methodologies give the errors in S o and fc of about a factor of 2 (Abercrombie 1995; Zobin & Havskov 1995).…”

Section: Development Of Earthquake Swarmmentioning

confidence: 99%

“…The only historic summit eruption occurred in 1977-1978(Yokoyama et al 1981 within the 600-m contour of the volcanic edifice ( Fig. 2).…”

Section: Gene R a L C H A R A C T E R I S T I C S O F V O L C A N I Cmentioning

confidence: 99%

The nature of volcanic earthquake swarm preceding the 2000 flank eruption at Usu volcano, Hokkaido, Japan

Zobin

Nishimura

Miyamura³

2005

Geophysical Journal International

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S U M M A R YThe 2000 eruption of Usu volcano, Hokkaido, occurred on the northwestern flank of volcano on March 31 at 13:07 (Local time), after about 4 days of intensive seismic activity. We study the seismic process prior to the eruption using the routine earthquake catalogue of the Japan Meteorological Agency (JMA) and the digital seismograms of the short-period station NBBT (JMA). Earthquakes began beneath the summit and southern slope of the volcano. Then seismic foci clustered along two linear zones intersecting to the south of the initial epicentral zone. The majority of earthquakes occurred at depth within the range between 4 and 7 km. The magnitude range of located earthquakes varied between 0.8 and 4.4. The earthquake epicentres did not reach the sites of the forthcoming eruption; they stopped at a distance of about 1-3 km. The eruption began during the ceasing of seismic activity. A study of the nature of the swarm was performed for a sample of 303 earthquakes with a magnitude interval from 2.5 to 3.4 that were representative of the swarm. Visual analysis allowed separating the earthquakes into two groups: 286 volcano-tectonic (VT) earthquakes and 17 long-period (LP) earthquakes. The spectral analysis of S waves of 274 VT earthquakes in the frame of Brune's model showed that the VT earthquakes may be separated into two groups as characterized by high stress drops (HSD) and low stress drops (LSD). The swarm began with HSD earthquakes. The LSD and LP earthquakes were recorded about 30-40 hr later, simultaneously with the beginning of deformation of volcanic edifice, and accompanied the HSD earthquakes up to the beginning of eruption. We attribute the HSD earthquakes to the probable product of magmatic thermal fracturing of host rocks. The relatively long LSD ruptures may be attributed to the slips along the pre-existing fractures during magma movement.

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High stress drop events in the Victoria, Baja California earthquake swarm of 1978 March

Cited by 25 publications

References 28 publications

Seismic Anisotropy Observations in the Mexicali Valley, Baja California, M�xico

Seismic Anisotropy Observations in the Mexicali Valley, Baja California, M�xico

Stress Drop during Earthquakes: Effect of Fault Roughness Scaling

The nature of volcanic earthquake swarm preceding the 2000 flank eruption at Usu volcano, Hokkaido, Japan

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