Short-period nonseismic tilt perturbations and their relation to episodic slip on the San Andreas Fault in central California

McHugh, Stuart; Johnston, M. J. S.

doi:10.1029/jb081i035p06341

Cited by 33 publications

(10 citation statements)

References 16 publications

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“…The episodic character probably results from the failure characteristics of near-surface materials (such as soils) and does not reflect the general fault behavior. Similar conclusions are also indicated in surface tilt measurements around the fault during creep events McHugh and Johnston, 1976;Mortensen et al, 1977]. It is possible that this conclusion will be modified if the fault zone rigidity is substantially less than that of the surrounding material and strain and tilt fields attenuate more rapidly as a function of distance from the fault than might be expected on the basis of dislocation modeling in an elastic half space.…”

Section: Resultssupporting

confidence: 62%

Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Johnston¹,

Jones²,

Daul³

1977

J. Geophys. Res.

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Continuous strain measurements from 3 three-component invar wire strainmeters installed 1200, 1500, and 1700 m from the San Andreas fault indicate no observable strain change at the instrument resolution (< 10 -8) during 10 episodic creep events on the fault. These strain observations indicate that the slip area responsible for the creep observations is near surface and of quite limited extent. The episodic creep character probably results from the failure properties of near-surface materials rather than general fault behavior, which is better indicated perhaps by averaged creep. Deeper slower slip apparently loads the surface material. Longer-term strain changes (410-*) do occur, but the form of the signal is not what would be expected from simple models, nor is it consistent, for successive events. The amplitude does not increase with creep event amplitude, and similar changes occur without creep events. Deeper slip on the San Andreas fault apparently is smoother than would be inferred from the duration of episodic creep observations. Unfortunately, signal discrimination capability gets worse at longer periods and needs improvements if slow deformation waves are to be detected at strain levels below 10 -7.

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Section: Resultssupporting

confidence: 62%

Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Johnston¹,

Jones²,

Daul³

1977

J. Geophys. Res.

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“…Tectonically induced creep events in tilt data have repeatedly been observed near major faults in California (Johnston et al . 1976; McHugh & Johnston 1976; Mortensen et al . 1977; Wesson 1988 and references therein).…”

Section: Various Types Of Tilt Signalsmentioning

confidence: 99%

Point stability at shallow depths: experience from tilt measurements in the Lower Rhine Embayment, Germany, and implications for high-resolution GPS and gravity recordings

Kümpel

Lehmann

Fabian

et al. 2001

Geophysical Journal International

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Summary From 1996 to 1999, we have studied ground tilts at depths of between 2 m and 5 m at three sites in the Lower Rhine Embayment (LRE), western Germany. The LRE is a tectonically active extensional sedimentary basin roughly 50 km × 100 km. The purpose of the tilt measurements was (a) to provide insight into the magnitude, nature and variability of background tilts and (b) to assess possible limitations of high‐resolution GPS campaigns and microgravity surveys due to natural ground deformation. The tilt readings, sensed by biaxial borehole tiltmeters of baselength 0.85 m, cover a frequency range from 10−8 Hz to 10−2 Hz (periods from minutes to years). Assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters' baselength, and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity, we try to estimate the magnitude level of point movements and corresponding Bouguer gravity effects that is generally not surpassed. The largest tilt signals observed were some ± 50 µrad yr−1. If they were observable over a ground section of extension, e.g. 10 m, the converted rates may correspond to about ± 0.5 mm per 10 m yr−1 in vertical ground displacement, and ± 0.1 µgal yr−1 in Bouguer gravity effect, respectively. Large signals are mostly related to seasonal effects, probably linked to thermomechanical strain. Other causes of ground deformation identified include seepage effects after rainfalls (order of ± 10 µrad) and diurnal strains due to thermal heating and/or fluctuations in the water consumption of nearby trees (order of ± 1 µrad). Episodic step‐like tilt anomalies with amplitudes up to 22 µrad at one of the observation sites might reflect creep events associated to a nearby active fault. Except for short‐term ground deformation caused by the passage of seismic waves from distant earthquakes, amplitudes of non‐identified tilt signals in the studied frequency range seem not to exceed ± 2 µrad. As the larger tilt signals are close to the precision achieved with modern GPS systems and superconducting gravimeters when converted into height and gravity changes, further enhancement in resolution of these techniques may require simultaneous recording of local ground deformation at the observation sites.

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“…Berger and Levine's data are substantially quieter than data obtained from a 10-m wire strainmeter operated at the earth's surface [Sinvhal, 1973]. Further evidence for the existence of small-scale surface noise is implied by the general lack of coherence of the data from small borehole tiltmeters installed in near-surface arrays (see, for example, McHugh and Johnston [1976]).…”

Section: Introductionmentioning

confidence: 99%

Thermally induced errors in fluid tube tiltmeters

Beavan¹,

Bilham²

1977

J. Geophys. Res.

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The effects of temperature variations on the tilt measured by long fluid tube tiltmeters are examined in detail. Temperature effects are important both in instruments which measure tilt as changes in fluid level between the ends of a fluid-filled tube and in instruments which measure tilt as changes in fluid pressure. Methods are outlined for reducing temperature effects in both types of tiltmeters. A new temperaturecompensating method for fluid pressure tiltmeters is demonstrated both in theory and in practice. The method requires that the fluid-filled tube(s) connecting the pressure transducer to the end reservoir(s) be laid at a constant small angle to the horizontal. Tiltmeters which use a horizontal half-filled fluid tube are recommended on the grounds of long-term stability and freedom from temperature effects.

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Short-period nonseismic tilt perturbations and their relation to episodic slip on the San Andreas Fault in central California

Cited by 33 publications

References 16 publications

Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Point stability at shallow depths: experience from tilt measurements in the Lower Rhine Embayment, Germany, and implications for high-resolution GPS and gravity recordings

Thermally induced errors in fluid tube tiltmeters

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