Coseismic Surface Displacements Research Articles

Source parameters of the 1908 Messina Straits, Italy, earthquake from geodetic and seismic data

We carry out a nonlinear joint inversion of P wave first‐motion polarities and coseismic surface displacement data of the 1908 Messina earthquake. We model the earthquake using a single planar fault: Slip is at first assumed to be uniform across the whole fault, then independent in a small set of coplanar subfaults, and finally smoothly variable across the fault. The first two steps are accomplished using a global minimization technique. The main features of the retrieved model are very robust and independent of the seismic velocity profile, of the presence of questionable bench marks, and of the assumed residual distribution. The along‐strike component of slip is about half the along‐dip component, in agreement with the direction of the extensional stress axis retrieved from geological observations. Surface vertical displacement is consistent with tsunami data and with the morphology of the Messina Straits.

The Mw 7.1, Hector Mine, California earthquake: surface rupture, surface displacement field, and fault slip solution from ERS SAR data

Abstract The Mw7.1, Hector Mine, California earthquake of October 16, 1999 produced a 50 km-long surface rupture, ∼20 km east of the surface rupture of the 1992 Landers earthquake. ERS2 radar data acquired before and after the event provide geodetic measurements of two components of the co-seismic surface displacement field. (1) Interferometric processing of the data provides the range (radar line of sight) component of the displacement field with a precision of a few millimeters. (2) The sub-pixel correlation of the before and after amplitude images provides a second component of the surface displacement field, parallel to the satellite track, with a precision of ∼20 cm. The azimuth offset map reveals a ∼50 km long, NNW surface rupture formed of three sections: a N40°W southern section following the Bullion fault, a N10°W central section cutting through the Bullion Mountains, and a northern N40°W section extending up to the Lavic Lake. A north–south-trending, localized gradient in the azimuth offset field suggests that the central section of the fault extends to the north at depth over a distance of ∼10 km. The slip distribution curve constructed using the azimuth offsets has a bell shape, with a maximum of 6.5 m at the north end of the central fault section. The fault slip model derived from the inversion of the azimuth and from range displacement data indicates that 3–5.8 m of right-lateral slip occurred between the depths of 0 and 8 km along the northern and the central sections of the fault. The solution bears a down-dip component of slip of ∼2 m, west side down, along the southern part of the northern fault section. The down-dip component of slip is consistent with compression on a northeast dipping fault.

The complete (3‐D) surface displacement field in the epicentral area of the 1999 MW7.1 Hector Mine Earthquake, California, from space geodetic observations

We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co‐seismic surface displacement field due to the 1999 Mw7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike‐slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry.

First study of fault trench stratigraphy at Mt. Etna volcano, Southern Italy: understanding Holocene surface faulting along the Moscarello fault

Paleoseismology, the study of past earthquakes based on their geological record in the stratigraphy and landscape, is a successful newly developing field of research. The application of fault trench studies in volcanic environments is one of the youngest branches of paleoseismology. In this paper, we present the results of the first exploratory trenches excavated at Mt. Etna in Sicily, the largest European volcano. Modern surface faulting at Etna is a very well known feature, which poses significant hazard to the local community, both in terms of ground displacement of essential lifelines and ground shacking from frequent damaging earthquakes. However, while the geomorphology and the seismicity of the active fault in the Etna region consistently show very high rates of tectonic activity, the Holocene cumulative throw and slip-rates, along with the nature (coseismic vs. creeping fault slip), dimension and timing of the displacement events, are still poorly constrained. For this purpose, we selected as a sample area the Moscarello fault, one of the most outstanding segment of the Timpe system of active normal faults in the volcano’s lower eastern flank. Displaced landforms and volcanic units at the Fondo Macchia basin, in the central sector of this fault, indicate some hundreds of meters of vertical offset in the last ca. 80 kyr, with a long-term slip-rate substantially higher than 1.5–2.0 mm/yr. According to the historical sources and instrumental observations, the Moscarello fault ruptured four times in the last 150 years during shallow ( H < 5 km) and moderate magnitude ( M < 4.8) earthquakes. These events were associated with severe damage in a narrow epicentral area (macroseismic intensities up to the IX–X grade of the MSK scale) and extensive surface faulting (end-to-end rupture length up to 6 km, vertical offsets up to 90 cm). This clearly indicates very high modern rates of deformation along this fault. We conducted trench investigations at the Fondo Macchia site, in a point where eyewitnesses observed ca. 20 cm of coseismic vertical displacement after the April 21, 1971, M s =3.7 , earthquake. The excavated sections provided direct stratigraphic evidence for a vertical slip-rate of 1.4–2.7 mm/yr in the last ca. 6 kyr. This should be regarded as a minimum slip-rate for the central section of the fault. We explored a single scarp at a single site, while we know from recent historical observations that several parallel scarps may rupture coseismically at Fondo Macchia. Thus, the relevant deformation rate documented for the modern period might be likely extended back in the past to a time-span of some thousands of years at least. As expected, for such a volcanic environment, the activity rates of the Moscarello fault are also significantly higher than for the Apennines normal faults, typically showing slip-rates lower than 1 mm/yr. The agriculturally reworked trench hangingwall stratigraphy did not allow to recognize individual displacement events. Nevertheless, the sedimentary structures observed in the trench footwall strongly suggest that, as for the last 150–200 years of detailed historical record, fault behavior at Fondo Macchia is governed by coseismic surface displacement rather than fault creep. This research confirms that paleoseismology techniques can be effectively applied also in active volcanic environments, typically characterized by rheology and, consequently, seismicity and fault dynamics very different from those of other tectonic environments in which paleoseismology has been firstly developed and is today extensively applied.

The September 26, 1997 Colfiorito, Italy, earthquakes: Modeled coseismic surface displacement from SAR interferometry and GPS

The largest events of the 1997 Umbria‐Marche seismic sequence were the two September 26 earthquakes of Mw = 5.7 (00:33 GMT) and Mw = 6.0 (09:40 GMT), which caused severe damage and ground cracks in a wide area around the epicenters. We created an ERS‐SAR differential interferogram, where nine fringes are visible in and around the Colfiorito basin, corresponding to 25 cm of coseismic surface displacement. GPS data show a maximum horizontal displacement of (14±1.8) cm and a maximum subsidence of (24±3) cm. We used these geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes. Modeled fault depths and maximum slip amplitudes are 6.5 km and 47 cm for the first event and 7 km and 72 cm for the second one, in good agreement with those derived from the seismological data.

The 1997 May 10 Zirkuh (Qa'enat) earthquake (Mw 7.2): faulting along the Sistan suture zone of eastern Iran

Summary The destructive Zirkuh-e-Qa’enat earthquake of 1997 May 10 (Mw 7.2, Ms 7.3, mb 6.3) produced 125 km of NNW–SSE right-lateral strike-slip surface faulting on the Abiz fault in the Sistan suture zone of eastern Iran: the longest known surface rupture associated with an Iranian earthquake. Analysis of the body-wave seismograms from the main shock shows that rupture occurred in four main subevents, propagating in a sequence from north to south. Although predominantly strike-slip, the orientation of the faulting in each subevent varies, with appreciable reverse components in the north-central part and at the southern end of the Abiz fault. This change in fault style along the Abiz fault inferred from the seismograms is also seen in the coseismic surface ruptures and the geomorphology. Average coseismic surface displacements were approximately 2 m, implying a static stress drop of only 5 bar (0.5 MPa). The 1997 surface ruptures followed clear traces of late Quaternary slip on the Abiz fault, and for its northern 50 km re-ruptured fault segments that had slipped in previous earthquakes of Ms 6.0–6.6 in 1936 and 1979. The 1997 earthquake ruptured the northern end of the N–S right-lateral strike-slip system of the Sistan suture zone, ending where it abuts a system of E–W left-lateral strike-slip faults which have also slipped in large earthquakes during the last 30 years. The earthquakes on this conjugate system of strike-slip faults form a sequence that may have been triggered by the enhancement of stress on one fault as a result of slip on a neighbouring fault. Together, these faults achieve N–S right-lateral shear of deforming Iran against stable western Afghanistan by N–S slip on the right-lateral faults and clockwise rotation of the E–W left-lateral faults.

Surface displacement of the March 26, 1997 Kagoshima‐Ken‐Hokuseibu Earthquake in Japan from synthetic aperture radar interferometry

A JERS 1 differential L‐band synthetic aperture radar (SAR) interferogram of the March 26,1997 Kagoshima‐ken‐hokuseibu earthquake (Mw=6.1) in southwestern Japan shows about 9 cm peak‐to‐peak coseismic surface displacement in the radar line‐of‐sight (LOS) direction. A permanent GPS array detected 1 to 2 cm horizontal displacements from this earthquake. By inverting the SAR and GPS data together, we estimated a fault mechanism without any seismological data. A theoretical radar LOS displacement pattern from a single fault model of the earthquake motion matches the SAR and GPS observations closely. The model assumes left lateral slip of 0.46 cm with rake angle of 19° on a rectangular fault plane of dimensions 11 km (width) by 12 km (length). We demonstrate that L‐band SAR interferometry can describe several cm surface displacement in detail and construct a fault model. However, despite the acquisitions being during the cold season, there are apparent water vapor signatures in the interferogram with equivalent path delays of up to 1.5 cm.

Paleoseismic indications along ‘aseismic’ fault segments in the guadalentín depression (SE Spain)

The Guadalentín Depression, located in SE Spain (Murcia Region), is bounded by two of the main NE-SW master faults of the Eastern Betics Cordilleras: The Lorca-Alhama and the Palomares left-lateral strike-slip faults. Available earthquake data indicate that, in the last 600 years, some sectors of the Lorca-Alhama Fault and the entire sector of the Palomares Fault have not been associated with significant historical seismicity. However, they show a wide range of diagnostic features of earthquake surface displacements on late Pleistocene and Holocene alluvial and colluvial surfaces. Aside from the left-lateral offsets recorded along 045–050 ° master fault strands of the Lorca-Alhama Fault, major paleoseismic surface displacements show different kinematics in relation to the broad orientation of the fault strands: (1) vertical normal displacements along 010–020 ° trending faults mainly preserved as degraded fault scarps of 2.5-1.8 m high (Aljibejo site); and (2) vertical reverse displacements, with average offsets of 0.2 – 1 m, along 065–080 ° subsidiary faults. In this last group, the younger one (Carraclaca Baths site) remains as a fault scarp of 0.8 m height affecting a cascade tufa which was active until the Spanish Roman Period (2nd Century B.C. to 6th Century A.D.). In other cases, reverse offsets resulted in smaller displacements (0.26 m) of paleosols, but show a recurrent behaviour (La Escarihuela site). The strongest earthquakes recorded in the study area did not exceed more than Mb 4.5 or MSK Intensity VIII (historical) with no evidence of coseismic rupture. Therefore, the preliminary data presented here seem to indicate that the paleoseismic activity on both faults is capable of producing coseismic surface displacements, probably reaching magnitudes of at least 6.5. These data show that paleoseismic studies based on geomorphological analyses are a useful tool in the assessment of the relative degree of activity of apparently ‘aseismic’ fault traces.

Effective relaxation time and viscosity of the earth inferred from the postseismic vertical deformations of the 1990 M S=7.0 Gonghe earthquake

The postseismic vertical deformation rates of the 1990 Gonghe M S=7.0 earthquake appears to have decreased exponentially. Based on Okada’s coseismic surface displacement solution caused by a uniform fault slip in an elastic homogeneous half space, we derived its postseismic surface displacement by using a single-layer standard linear solid model, and further derived a simplified formula for determining the effective relaxation time and viscosity of the earth, which is independent of the dislocation parameters of the causative fault. From the postseismic vertical deformation of the 1990 Gonghe earthquake, we inferred that the effective relaxation time defined by τ=η/μ is 2.6 years, and the effective viscosity η is about 1018 Pa · s.

Fault propagation fold growth during the 1994 Northridge, California, earthquake?

Geological models of buried thrust faults indicate that fault propagation folds (FPF) form and grow with a geometry that depends on that of the fault (Suppe, 1985; Suppe and Medwedeff, 1990). The displacement gradient fields for faults and kink folds are very similar, and both can be modeled using dislocations. In this paper we test a geological model of the FPF associated with the January 17, 1994 Northridge, California, earthquake to determine whether folding along axial planes inferred from geologic models accounts in part for the coseismic surface displacements measured with Global Positioning System (GPS). We test for coseismic deformation on both the main rupture plane and active axial planes of related folds by inverting for the displacements on dislocation planes in an elastic half‐space. A model incorporating two axial planes is preferred to a model with a single rupture plane in a normalized root mean square (NRMS) sense; however, the distribution of axial plane displacements does not correlate with the displacements on the main rupture plane in the way expected for a fault propagation fold. Our results indicate that the deformation associated with folding is too distributed to be resolved on a discrete plane, that the deformation occurs interseismically, or that one or both of the kink bands does not exist. A model of a single elevated plane, which is parallel to, but not coplanar with, the aftershocks, is better in a NRMS sense than the FPF model, indicating that anelastic deformation in the hanging wall may be distributed.

Static stress changes and earthquake triggering during the 1954 Fairview Peak and Dixie Valley earthquakes, central Nevada

AbstractThe 16 December 1954 Dixie Valley (MS 6.8) earthquake followed the Fairview Peak (MS 7.2) earthquake by only 4 min and 20 sec. A three-dimensional model of the two dip-slip fault systems based on recent detailed field studies shows the ruptures were separated by a 6-km step in surface trace. A boundary-element approach shows that the static stress changes imposed by rupture of the Fairview Peak earthquake are in the correct sense to explain the northward propagation of faulting along four distinct faults that comprise the Fairview Peak earthquake and the subsequent triggering of the Dixie Valley earthquake. The location of rupture end points at sites where static stresses change sign is also used to suggest that static stress changes may play a role in controlling the extent of fault ruptures. We also observe that the largest coseismic surface displacements tend to correlate with those sections of the faults showing the largest positive stress change from preceding ruptures.

The 1992 M = 7 Cape Mendocino, California, earthquake: Coseismic deformation at the south end of the Cascadia megathrust

We invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the April 25, 1992, M = 7 Cape Mendocino, California, earthquake. The orientation of the model slip vector, which nearly parallels North America‐Juan de Fuca relative plate convergence, and the location and orientation of the model fault relative to the offshore Cascadia megathrust, suggest that the 1992 Cape Mendocino earthquake is the first well‐recorded event to relieve strain associated with the Cascadia subduction zone. We use data from three geodetic techniques: (1) the horizontal and vertical displacements of 13 monuments surveyed with the Global Positioning System, corrected for observed horizontal interseismic strain accumulation, (2) 88 section‐elevation differences between leveling monuments, and (3) the uplift of 12 coastal sites observed from the die‐off of intertidal marine organisms. Maximum observed displacements are 0.4 m of horizontal movement and 1.5 m of uplift along the coast. We use Monte Carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties. The optimal model using all the data resolves 4.9 m of slip on a 14 by 15 km fault that dips 28° SE. The fault extends from 1.5 to 8.7 km in depth and the main‐shock hypocenter is close to the downdip projection of the fault. The shallowly dipping fault plane is consistent with the observed aftershock locations, and the estimated geodetic moment is 3.1 × 1019 N m, 70% of the seismic moment. Other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry. If the earthquake is characteristic for this segment, the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years, with a 95% confidence range of 100–670 years. The coseismic uplift occurred in a region that also has high Quaternary uplift rates determined from marine terrace studies. If repeated ruptures of this southernmost segment of the Cascadia megathrust are responsible for the Quaternary uplift, a comparison of the coseismic uplift with coastal uplift rates suggests a recurrence interval of 200–400 years. Thus comparing horizontal and vertical coseismic to long‐term deformation suggests a recurrence interval of about 100–300 years for M = 7 events at the south end of the Cascadia megathrust.

95/04436 Properties and structure of hard coals from the borehole Niedobezyce IG-1 in the Rybnik Coal District, Upper Silesian Coal Basin, their petrog

On 20 July 2017 (22:31:10 UTC), an Mw6.6 earthquake took place offshore Kos Island, in the southeastern (SE) Aegean Sea, producing severe damage and loss of life in the city of Kos and several smaller cities and villages both in Kos Island (Greece) and in the Bodrum peninsula (Turkey). All available seismological data until the end of October 2017 were gathered from seismological stations located in Greece and Turkey for the relocation process. The relocated aftershocks are clustered at least in three distinctive patches, creating a zone reaching a total length of about 40 km, elongated in a nearly east-west direction, and are mainly concentrated at depths 8–15 km, with the main shock hypocenter placed at ~13 km, implying a seismogenic layer of 7 km thickness, indicative for normal faulting earthquakes with Mmax ~ 6.5. The aftershock fault plane solutions are predominantly normal faulting in response to the north–south extension of the back arc Aegean area and consistent with the broader regional stress field. We also applied the satellite radar interferometry (InSAR) technique to define the coseismic surface displacements, revealing the range of deformation on the Island and the surrounding mainland. We combined this deformation field along with the available vectors of displacement measured by the Global Navigation Satellite System (GNSS) technique with the seismological data to determine the fault geometry and rupture process. The resulted variable slip model indicates a rather elliptical rupture area of 306 km2, with the coseismic slip ranging between 0.5 and 2.3 m. The peak moment release occurred in the depth interval of 9–11 km, consistent with the depth distribution of seismicity in the study area. We used the variable slip model to calculate Coulomb stress changes and investigate possible triggering due to stress transfer to the nearby fault segments.

Analysis of coseismic surface displacement gradients using radar interferometry: new insights into the Landers earthquake: G. Peltzer, K. W. Hudnut & K. L. Feigl, Journal of Geophysical Research, 99(B11), 1994, pp 21,971–21,981

Analysis of coseismic surface displacement gradients using radar interferometry: new insights into the Landers earthquake: G. Peltzer, K. W. Hudnut & K. L. Feigl, Journal of Geophysical Research, 99(B11), 1994, pp 21,971–21,981

Geodetic data inversion using a Bayesian information criterion for spatial distribution of fault slip

SUMMARY We developed a new inversion method to reconstruct static images of seismic sources from geodetic data, using Akaike’s Bayesian Information Criterion (ABIC). Coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations. Parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form. Incorporating prior constraints on the smoothness of slip distribution with the observation equations, we construct a Bayesian model with unknown hyperparameters. The optimal values of the hyperparameters, which control the structure of the Bayesian model, are objectively determined from observed data by using ABIC. Once the values of hyperparameters are determined, we can use the maximum likelihood method to find the optimal distribution of fault slip. We examined the validity of this method through a numerical experiment using theoretical data with random noise. We analysed geodetic data associated with the 1946 Nankaido earthquake (Ms = 8.2) by using this method. The result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m, located off Kii Peninsula and Muroto Promontory. These two high-slip areas are clearly separated by a low-slip zone extending along Kii Strait. Such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part.

Rupture of the 4 February 1976 Guatemalan earthquake

Abstract An expanded body-wave data set for the 4 February 1976 Guatemalan earthquake is analyzed by iterative, multiple-station inversion to provide enhanced resolution of the rupture process of this important strike-slip event. The body-wave data set used in an earlier study of this event, in which a predominantly unilateral, westward-propagating rupture was proposed, actually does not have sufficient resolution to reliably map the spatial heterogeneity for the source process. The expanded azimuthal coverage of the new data set provides better spatial resolution of the primary rupture characteristics. The Guatemalan earthquake can be modeled as an asymmetric bilateral rupture extending eastward and westward along the Motagua fault, with the largest episode of moment release occurring ≈90 km west of the epicenter, near a change in strike in the surface faulting. The overall rupture velocity is about 3.5 km/sec, and the total moment is 3.7 × 10 27 dyne cm. Inversions with composite fault models having a second focal mechanism appropriate for the western end of the fault are consistent with the data, but are not clearly required. The characterization of the Guatemalan earthquake as an irregular bilateral rupture agrees with the variable co-seismic surface displacements measured along the fault outcrop as well as with an earlier surface-wave investigation, and is consistent, in a general sense, with previous characterizations of the irregular rupture processes of other large strike-slip earthquakes such as the 1972 Sitka, Alaska and the 1980 Eureka, California events.

Rupture process of theMs6.6 Superstition Hills, California, earthquake determined from strong-motion recordings: Application of tomographic source inversion

AbstractWe analyze strong-motion recordings of the Ms 6.6 Superstition Hills earthquake to determine the timing, location, spatial extent, and rupture velocity of the subevents that produced the bulk of the high-frequency (0.5 to 4 Hz) seismic energy radiated by this shock. The earthquake can be characterized by three principal subevents, the largest ones occurring about 3 and 10 sec after initiation of rupture. Timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the Superstition Hills fault. The two largest subevents display different directivity effects. We apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance, based on a one-dimensional fault model. The azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the Superstition Hills fault at a velocity about equal to the P-wave velocity. An alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent, but it is not supported by the aftershock distribution. The third subevent ruptured to the southeast along an 8-km long portion of the Superstition Hills fault at about the shear-wave velocity. This rupture propagation caused the relatively large accelerations and velocities observed in strong-motion records for stations southeast of the hypocenter. The long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development. The southern half of the Superstition Hills fault did not generate significant high-frequency strong ground motion, although it showed substantial co-seismic surface displacement. The subevents are situated along the same northern portion of the fault where most of the aftershocks are located. The locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth.