Nicaragua Earthquake Research Articles

Near-real time tsunami inundation forecast for Central America : case study of the 1992 Nicaragua tsunami earthquake

ABSTRACT A near-field tsunami inundation forecast method (NearTIF) for the Pacific coast of Central America is developed and tested on the basis of the 1992 Nicaragua tsunami earthquake case. The appropriate source model of the 1992 Nicaragua earthquake, estimated using the W-phase inversion with a depth dependent rigidity curve from a previous study, is used as a reference model to test the proposed NearTIF method. The tsunami inundation along the Pacific coast of Nicaragua is computed from the reference model of the 1992 Nicaragua earthquake. The tsunami inundation obtained using the NearTIF method matches the tsunami inundations computed from the reference model. The tsunami heights and the tsunami inundation of the 1992 Nicaragua tsunami surveyed by a previous study are roughly matched by the tsunami inundations obtained using the NearTIF method in this study. Although the computational time for the tsunami inundation from the reference source model is about 95 min, the computational time plus the database search time for the NearTIF method is approximately 2–4 min. The method presented in this study can be used as a near-real time tsunami inundation forecast method for the Pacific coast of Central America.

Simulation of a Dispersive Tsunami due to the 2016 El Salvador\u2013Nicaragua Outer-Rise Earthquake (Mw 6.9)

The 2016 El Salvador–Nicaragua outer-rise earthquake (Mw 6.9) generated a small tsunami observed at the ocean bottom pressure sensor, DART 32411, in the Pacific Ocean off Central America. The dispersive observed tsunami is well simulated using the linear Boussinesq equations. From the dispersive character of tsunami waveform, the fault length and width of the outer-rise event is estimated to be 30 and 15 km, respectively. The estimated seismic moment of 3.16 × 1019 Nm is the same as the estimation in the Global CMT catalog. The dispersive character of the tsunami in the deep ocean caused by the 2016 outer-rise El Salvador–Nicaragua earthquake could constrain the fault size and the slip amount or the seismic moment of the event.

Method to Determine Appropriate Source Models of Large Earthquakes Including Tsunami Earthquakes for Tsunami Early Warning in Central America

Large earthquakes, such as the Mw 7.7 1992 Nicaragua earthquake, have occurred off the Pacific coasts of El Salvador and Nicaragua in Central America and have generated distractive tsunamis along these coasts. It is necessary to determine appropriate fault models before large tsunamis hit the coast. In this study, first, fault parameters were estimated from the W-phase inversion, and then an appropriate fault model was determined from the fault parameters and scaling relationships with a depth dependent rigidity. The method was tested for four large earthquakes, the 1992 Nicaragua tsunami earthquake (Mw7.7), the 2001 El Salvador earthquake (Mw7.7), the 2004 El Astillero earthquake (Mw7.0), and the 2012 El Salvador–Nicaragua earthquake (Mw7.3), which occurred off El Salvador and Nicaragua in Central America. The tsunami numerical simulations were carried out from the determined fault models. We found that the observed tsunami heights, run-up heights, and inundation areas were reasonably well explained by the computed ones. Therefore, our method for tsunami early warning purpose should work to estimate a fault model which reproduces tsunami heights near the coast of El Salvador and Nicaragua due to large earthquakes in the subduction zone.

A rapid estimation of near‐field tsunami runup

AbstractMany efforts have been made to quickly estimate the maximum runup height of tsunamis associated with large earthquakes. This is a difficult task because of the time it takes to construct an accurate tsunami model using real‐time data from the source. It is possible to construct a database of potential seismic sources and their corresponding tsunami a priori. However, such models are generally based on uniform slip distributions and thus oversimplify the knowledge of the earthquake source. Here we show how to predict tsunami runup from any seismic source model using an analytic solution that is specifically designed for subduction zones with a well‐defined geometry, i.e., Chile, Japan, Nicaragua, and Alaska. The main idea of this work is to provide a tool for emergency response, trading off accuracy for speed. The solutions we present for large earthquakes appear promising. Here runup models are computed for the following: the 1992 Mw 7.7 Nicaragua earthquake, the 2001 Mw 8.4 Perú earthquake, the 2003 Mw 8.3 Hokkaido earthquake, the 2007 Mw 8.1 Perú earthquake, the 2010 Mw 8.8 Maule earthquake, the 2011 Mw 9.0 Tohoku earthquake, and the recent 2014 Mw 8.2 Iquique earthquake. The maximum runup estimations are consistent with measurements made inland after each event, with a peak of 9 m for Nicaragua, 8 m for Perú (2001), 32 m for Maule, 41 m for Tohoku, and 4.1 m for Iquique. Considering recent advances made in the analysis of real‐time GPS data and the ability to rapidly resolve the finiteness of a large earthquake close to existing GPS networks, it will be possible in the near future to perform these calculations within the first minutes after the occurrence of similar events. Thus, such calculations will provide faster runup information than is available from existing uniform‐slip seismic source databases or past events of premodeled seismic sources.

Thermal constraints on the frictional conditions of the nucleation and rupture area of the 1992 Nicaragua tsunami earthquake

SUMMARY The 1992 Nicaragua earthquake was a ‘tsunami earthquake’, which generated tsunamis disproportionately large for its surface wave magnitude Ms = 7.2. Seismological studies and tsunami simulation indicated that the event was a slow earthquake, which occurred on the plate boundary between the subducting Cocos plate and the overriding Caribbean plate. We present a finite element model that enables us to estimate for the first time the temperature and inferred frictional conditions in the rupture area of a tsunami earthquake. Direct and indirect observations are used to constrain all model parameters, and surface heat-flux measurements provide independent information to verify the model results. Furthermore, we used a genetic algorithm to perform a sensitivity analysis of all model parameters and to define the spatial range of thermally defined updip limit of the seismogenic zone. The earthquake nucleated in the seismogenic zone at temperatures of ∼150 ◦ C and propagated updip towards the trench axis. The centroid or centre of mass of moment release was located in a region characterized by temperatures of ∼50 ◦ C. Thus, the rupture propagated through a region where plate motion is normally accommodated by aseismic creep. Our observations support a model in which tsunami earthquakes nucleate in the seismogenic zone near its updip limit. However, in such an environment coupled asperities are perhaps too small to cause large earthquakes. Seamounts, however, are abundant on the incoming Cocos plate. Therefore, in addition to temperature-dependent metamorphic induration of sediments, increased normal stress by seamount subduction may contribute to accumulate stress sufficiently large to release enough energy near the updip limit of the seismogenic zone to promote dynamic slip along a )

The 1994 Java tsunami earthquake: Slip over a subducting seamount

On June 2, 1994, a large subduction thrust earthquake (Ms 7.2) produced a devastating tsunami on the island of Java. This earthquake had a number of unusual characteristics. It was the first recorded large thrust earthquake on the Java subduction zone. All of the aftershock mechanisms exhibit normal faulting; no mechanisms are similar to the main shock. Also, the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow, shallow rupture near the trench, similar to the 1992 Nicaragua earthquake. We first relocate the main shock and the aftershocks. We then invert long‐period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip. A dip of 12°, hypocenter depth of 16 km and moment of 3.5×l020 N m (Mw 7.6) give the best fit to the combined seismic data and are consistent with the plate interface geometry. The source spectrum obtained from both body and surface waves has a single corner frequency (between 10 and 20 mHz) implying a stress drop of ∼0.3 MPa. The main energy release was preceded by a small subevent lasting ∼12 s. The main slip occurred at ∼20 km depth, downdip and to the NW of the hypocenter. This area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount. We interpret the Java earthquake as slip over this subducting seamount, which is a locked patch in an otherwise decoupled subduction zone. We find no evidence for slow, shallow rupture. No thrust aftershocks are expected if the entire locked zone slipped during the main shock, but extension of the subducting plate behind the seamount would promote normal faulting as observed. It seems probable that such a source model could also explain the size and timing of the observed tsunami.

Application of Mwp to tsunami earthquake

Tsunami earthquake produces anomalously strong tsunamis for their surface wave magnitude. To issue accurate early tsunami warnings for tsunami earthquakes, it is critical to identify them as tsunamigenic events as early as possible. Here we show that a pulse width of P‐wave, which we use to calculate broadband moment magnitude Mwp, gives accurate estimates of source duration time. We find that we may identify 1992 Nicaragua earthquake as a possible tsunamigenic earthquake by using a combination of both Mwp and the source duration. Our result suggests that the combination of Mwp and the source duration will provide an effective tool to issue early tsunami warnings even for tsunami earthquakes which have anomalously long source duration.

Frequency-dependent relocation of the 1992 Nicaragua slow earthquake: an empirical Green's function approach

We present a two-step empirical Green's function analysis of the slow 1992 Nicaragua earthquake (Mw= 7.7). In the first step, a narrow-band cross-correlation method recovers (he relative source amplitude and phase-delay spectra between the main shock and a suitable empirical Green's function (EGF). The analysis is performed at 2mHz intervals from 4 to 44mHz, using first- and second-orbit fundamental-mode Rayleigh waves. From the low-frequency relative amplitudes, we obtain the differences in mechanism and depth between the main shock and the EGF, and we present a method to correct for such differences. In the second step, we use the relative spectra to relocate the main shock relative to the EGF position al a set of discrete frequencies. In addition, we invert the relative spectra for the relative source time functions, using both a positivity and a smoothing constraint. Unlike standard EGF deconvolution, the spectral resolution achieved in our cross-correlation method allows us to determine the conditions of validity of the EGF approach. From our analysis, it appears that the centre of low-frequency radiation (4-10 mHz) during the slow 1 992 Nicaragua earthquake is situated about 40 km trenchwards of the epicentre. Between 20 and 44 mHz, centroids occupy intermediate positions between the low-frequency points and the epicentre. Relative source time functions have an average duration of about 120 s. They reveal a slow (∼ 1 km s1-), smooth component of rupture with unilateral directivity towards the SE along the trench axis. A large amount of slip occurred at shallow depths at the interface between the subducted Cocos plate and the Caribbean plate, in agreement with tsunami models of the event. The low-frequency radiation appears to originate from a zone devoid of teleseismic aftershocks. This suggests that unusual frictional properties at the plate interface, perhaps related to subducted sediments, are responsible for the slow and smooth nature of the 1992 Nicaragua earthquake.

Detecting slow, long-duration slip of large earthquakes using very long-period orbital surface waves

SUMMARY In this paper, we present a simple yet effective technique for measuring the source time-delay spectrum from very long-period world-circling surface waves without relying on assumed earth models or calculation of synthetic seismograms. By using autocorrelation and self-convolution functions derived from whole seismograms of large earthquakes recorded at a seismic station it is possible to isolate the source effects and precisely (5 5 s) determine the source delay spectrum at periods as long as 600 s. Measurements at such long periods are necessary for detecting slow precursory slip and slow creep after the main ‘fast’ seismic phase of large earthquakes. We apply this technique to five recent large earthquakes: the 1989 Macquarie Ridge (M, 8.2), the 1992 Nicaragua (M, 7.6), the 1993 Mariana Islands (M, 7.8), and the 1994 deep events in Fiji (M, 7.6) and Bolivia (M, 8.3). Our results are largely in agreement with the results obtained by other investigators. The Mariana Islands, Fiji, and Bolivia earthquakes had a normal rupture duration. The Nicaragua earthquake exhibits a source time-delay spectrum with the delay increasing from 31 s at the 100 s period to 50 s at the 600 s period, indicating an unusually slow rupture process. The Macquarie Ridge earthquake is anomalous by the discrepancy between the Love-wave and Rayleighwave estimates. Love waves, in the period band of 150 to 600 s, show a normal, flat source-delay spectrum with a delay of about 28 s. The Rayleigh-wave spectrum agrees with the Love-wave spectrum for periods smaller than 200 s and greater than 400 s; however, it shows a significantly shorter source delay (about 15 s) in the 250 to 350 s period range. The unusual nature of the Macquarie Ridge earthquake’s surface wave spectrum was pointed out by Ihmli, Harabaglia & Jordan (1993) who also provided an explanation in terms of a slow, precursory moment release. This explanation is not consistent with the flat Love-wave spectrum determined here.

The slip distribution of the 1992 Nicaragua Earthquake from tsunami run‐up data

The 2 September 1992 Nicaragua tsunami was induced by an MS≃ 7–7.3 earthquake and caused about 170 victims and significant damage to the coastal areas. The aim of this work is to infer the slip distribution along the causative seismic fault from the available tsunami run‐up field data. We have subdivided the fault plane into five slip‐independent subfaults and computed the corresponding numerical Green's functions by integrating shallow‐water equations via a finite‐element technique. The slip distribution on the fault has been determined by applying a least‐squares procedure to the differences between the observed run‐up values and the computed maximum water levels along the coast. The main result is that the best fit is found for a nonuniform coseismic slip, with the highest displacement taking place in the southernmost part of the fault. The measure of the improvement is given by the global rms residual of the heterogeneous‐slip case being circa 25% smaller than that of the uniform case. An ancillary outcome of the analysis is the evaluation of the mean amplification factor of the tsunami wave investing the Nicaraguan coast, that, on assuming a rigidity of 1×1010 N/m², results to be 3.45.

Linear and nonlinear computations of the 1992 Nicaragua earthquake tsunami

Numerical computations of tsunamis are made for the 1992 Nicaragua earthquake using different governing equations, bottom frictional values and bathymetry data. The results are compared with each other as well as with the observations, both tide gauge records and runup heights. Comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a smalI grid size is more effective than to include nonlinear terms in tsunami computation. Linear computation overestimates the amplitude for the later phase than the first arrival, particularly when the amplitude becomes large. The computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights; the average ratio, or the amplification factor, is estimated to be 3 in the present case when the grid size of 1 minute is used. The factor however may depend on the grid size for the computation.

Damage, conditions of East Java Tsunami of 1994 analyzed

On June 3, 1994, an Ms = 7.2 earthquake occured at a depth of 15 km near the east end of the Java trench in the Indian Ocean. The earthquake generated a large tsunami that violently struck southeast Java and extended to southwest Bali (Figures 1 and 2). Approximately 200 people were killed, 400 were injured, and 1000 houses were destroyed. Runup heights (Figure 2) ranged from 0–5 m in west Bali to 1–14 m in southeast Java.This unusual tsunami was generated about 250 km from the hardest hit area. Surprisingly, strong earthquake‐induced ground shaking was not a precursor so local residents had no warning of the impending catastrophe. The long‐period characteristics of the earthquake were incommensurate with the relatively weak high‐frequency magnitude Mb=5.5, and the rate of seismic moment release grew monotonically up to at least 270s. The pattern resembled that of the Nicaragua earthquake of September 2, 1992, in which strong ground shaking did not occur. Most of the damage was concentrated in villages located in pocket beaches, unlike previous tsunami damage in west Nicaragua, Flores, Indonesia [Yeh et al., 1993], and Okushiri, Japan.

Source characteristics of the 1992 Nicaragua tsunami earthquake inferred from teleseismic body waves

We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment is M o = 3.4 × 1020 Nm, which is consistent with the value determined from long-period surface waves, M o = 3.7 × 1020 Nm. The average rise time of dislocation is determined to be τ ≈ 10s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault width W = 50 km, we obtained the dislocation D = 1.3 m. From τ and D the dislocation velocity is D = D/τ ≈ 0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop Δσ = 1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2μE s /M o , where μ and E s are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than Δσ. The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion.

Magnitude scale for the Central American tsunamis

Based on the tsunami data in the Central American region, the regional characteristic of tsunami magnitude scales is discussed in relation to earthquake magnitudes during the period from 1900 to 1993. Tsunami magnitudes on the Imamura-Iida scale of the 1985 Mexico and 1992 Nicaragua tsunamis are determined to be m = 2.5, judging from the tsunami height-distance diagram. The magnitude values of the Central American tsunamis are relatively small compared to earthquakes with similar size in other regions. However, there are a few large tsunamis generated by low-frequency earthquakes such as the 1992 Nicaragua earthquake. Inundation heights of these unusual tsunamis are about 10 times higher than those of normal tsunamis for the same earthquake magnitude (M s = 6.9–7.2). The Central American tsunamis having magnitude m > 1 have been observed by the Japanese tide stations, but the effect of directivity toward Japan is very small compared to that of the South American tsunamis.

Near‐field deformation seen on distant broadband seismograms

Although far‐field body waves and surface waves are widely recognized, the improvements in broadband networks now allow the measurement of “near‐field” deformation of large earthquakes at great distances. Near‐field motions have been recognized previously only in theory and in close‐in recordings of earthquakes. We show examples from two recent events. For the large deep event on June 9, 1994 in Bolivia, there is a clear offset after the arrival of the P wave that has the amplitude expected for the near‐field term. In the shallow September 2, 1992 Nicaragua earthquake, the very long‐period motion observed between the P and S waves has roughly the amplitude expected from near‐field terms. Such near‐field terms are insensitive to earth structure, but supply information on long‐period source processes, and their observation begins to close the gap between long‐period seismology and geodesy.

Mechanism of the 1992 Nicaragua Tsunami Earthquake

The 1992 Nicaragua earthquake generated larger tsunamis than expected from its surface wave magnitude (Ms 7.2) and is known as a ‘tsunami earthquake’. Seismological studies showed that the duration was very long for its size, about 100 s. Other studies have shown that the seismic moment estimated from tsunamis is an order of magnitude larger than that from seismic waves, even after the long duration is accounted for. Numerical computations of tsunamis from various fault models are made to reconcile this discrepancy. Comparison of calculated waveforms with tide gauge records shows that the fault width is 40 km, much narrower than the aftershock area, and extends only into the upper 10 km of the ocean bottom. Slip amount on the fault is estimated to be 3 m from amplitude comparisons. The fault length is estimated to be 250 km, slightly longer than the aftershock area, from comparison of the tsunami height distribution. The rigidity around the shallow fault may be smaller than that of a standard underthrust fault, and the seismic moment is estimated as 3×1020 Nm, consistent with the seismic observations. A slow rupture on the shallow fault, presumably in the subducted sediments, is responsible to the unusually large tsunami excitation.

Tsunami field survey of the 1992 Nicaragua earthquake

An earthquake with surface magnitude (Ms ) 7.0 occurred 100 km off the Nicaraguan coast on September 2, 1992 (GMT). Despite its moderate size, this earthquake generated a sizable tsunami, which caused extensive damage along the coast of Nicaragua. In late September, about 170 people, mostly children, were listed dead or missing; 500 were listed injured; and over 13,000 were listed homeless, with more than 1500 homes destroyed. Damage was the most significant since the 1983 Japan Sea earthquake tsunami, which killed 100 people in Japan. The Flores (Indonesia) earthquake and tsunami of December 12, 1992, were more destructive than the Nicaragua or Japan Sea events.

The 1992 Nicaragua earthquake: a slow tsunami earthquake associated with subducted sediments

The 1992 Nicaragua earthquake was a ‘tsunami earthquake‘; that is, it generated tsunamis disproportionately large for its surface-wave magnitude, M_s. The moment magnitude, M_w, determined from long-period (~250-s) surface waves, was 7.6, significantly larger than the 20-s M_s of 7; this M_s–M_w disparity is also characteristic of tsunami earthquakes. The Nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks, allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms. We conclude that the Nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the Cocos and North American plates, and because of the absence of sediments on the trench floor offshore of Nicaragua, the slip propagated up-dip all the way to the ocean bottom, exciting large tsunamis. The occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction-zone thrust earthquakes. Our results reinforce the idea that tsunami warning systems using long-period (≥100-s) waves are necessary to reduce the hazard from this type of earthquake.

Determination of local magnitude, ML, from seismoscope records

A method is presented for determining the local magnitude, M_L, from records from seismoscopes and similar instruments. The technique extrapolates the maximum response of the standard Wood-Anderson seismograph, which determines M_L, from the maximum response of the seismoscope. The standard deviation of the steady-state response of an oscillator subjected to white noise excitation is used to derive a relation correcting for the different periods, dampings, and gains of the two instruments. The accuracy of the method is verified by application to data from the San Fernando and Parkfield earthquakes wherein both accelerograph and seismoscope records are available from the same sites. The accelerograms are used to synthesize Wood-Anderson responses whose maxima are compared to those extrapolated from the seismoscope data. In both earthquakes, the average magnitudes and standard deviations determined by the two approaches are very nearly equal. The method is then applied to the strong-motion data from the Managua, Nicaragua earthquake of December 23, 1972 (M_S = 6.2, mb = 5.6). A value of M_L = 6.2 is indicated from the seismoscope and accelerograph data. The next application is to the Guatemala earthquake of February 4, 1976 (M_S = 7.5, mb = 5.8). The only seismic instrumentation available for determining M_L is a seismoscope record from Guatemala City, which indicates M_L = 6.9 when a representative distance of about 35 km is used. As a final example, the records obtained during the 1906 San Francisco earthquake Formula from the Ewing duplex pendulum seismograph at Carson City, Nevada and the simple pendulum at Yountville, California are analyzed. After restoring the Carson City instrument, its period and damping were determined experimentally as were the period and damping of a similar instrument in the London Science Museum. On the basis of the strong-motion records from Carson City and Yountville, it is estimated that the local magnitude of the 1906 earthquake lies in the range Formula to 7. The use of seismoscope data further extends the instrumental base from which M_L can be determined and allows the rapid determination of M_L in earthquakes where seismoscope data are available. The applications in this study provide further instrumental evidence for the saturation of M_L in the 7 to Formula range, with the value of 7.2 for the Kern County earthquake of 1952, the largest so far determined.

Response of a reinforced concrete shear wall structure during the 1972 Managua earthquake

The 1972 Managua, Nicaragua earthquake was a severe test of modern earthquake resistant design and construction procedures. This paper examines the behaviour of the 18-story reinforced concrete Banco de America building which performed exceptionally well during the earthquake. Although the building suffered some structural and non-structural damage, its large, symmetrically located, coupled shear walls limited this damage to levels significantly below those observed in more flexible structures. Several linear elastic and nonlinear analyses were conducted to evaluate the building's behaviour and determine the probable cause of the observed damage. Both static and dynamic elastic analyses were used to determine the members that would have failed and the consequence of these failures on the subsequent dynamic response. The effects of biaxial ground motions, foundation flexibility and ground motion characteristics were considered in the elastic investigations. To get a better idea of the dynamic behaviour of the principal lateral force resisting system considered in the design, nonlinear analyses were performed for the coupled shear wall cores as constructed and for the idealized case where the coupling girders were assumed to have unlimited ductility. Even code type static analyses satisfactorily identified the damaged regions. The principal design deficiency was the low shear strength of the coupling girders. However, the nonlinear results indicated that had these girders been able to develop their flexural capacity they would have suffered substantial numbers of reversals and the shear walls would have been subjected to undesirable states of stress. The analytical results as well as the building’s performance demonstrated that buildings with coupled shear walls combined with moment resisting frames offer excellent protection against seismic excitations, minimizing nonstructural damage while providing several lines of defense in the event of localized failure. Design and repair recommendations are offered.