F. Ramón Zúñiga | Universidad Nacional Autónoma de México (original) (raw)

Papers by F. Ramón Zúñiga

Solid Earth, 2024

We derived scaling relationships for different seismic energy metrics for earthquakes around the ... more We derived scaling relationships for different seismic energy metrics for earthquakes around the globe with MW > 6.0 from 1990 to 2022. The seismic energy estimations were derived with two methodologies, the first based on the velocity flux integration and the second based on finite-fault models. In the first case, we analyzed 3331 reported seismic energies derived by integrating far-field waveforms. In the latter methodology, we used the total moment rate functions and the approximation of the overdamped dynamics to quantify seismic energy from 231 finite-fault models (Emrt and EO, EU, respectively). Both methodologies provide compatible energy estimates. The radiated seismic energies estimated from the slip models and integration of velocity records are also compared for different types of focal mechanisms (R, reverse; R-SS, reverse–strike-slip; SS, strike-slip; SS-R, strike-slip–reverse; SS-N, strike-slip–normal; N, normal; and N-SS, normal–strike-slip), and then used to derive converting scaling relations among the different energy types. Additionally, the behavior of radiated seismic energy (ER), energy-to-moment ratio (), and apparent stress (τα) for different rupture types at a global scale is examined by considering depth variations in mechanical properties, such as seismic velocities, rock densities, and rigidities. For this purpose, we used a 1-D global velocity model. The ratio is, based on statistical t tests, largest for strike-slip earthquakes, followed by normal-faulting events, with the lowest values for reverse earthquakes for hypocentral depths < 90 km. Not enough data are available for statistical tests at deeper intervals except for the 90 to 120 km range, where we can satisfactorily conclude that for R-SS and SS-R types is larger than for N-type faulting, which also conforms to the previous assumption. In agreement with previous studies, our results exhibit a robust variation in τα with the focal mechanism. Regarding the behavior of τα with depth, our results agree with the existence of a bimodal distribution with two depth intervals where the apparent stress is maximum for normal-faulting earthquakes. At depths in the range of 180–240 km, τα for reverse earthquakes is higher than for normal-faulting events. We find the trend EU > Emrt > EO for all mechanism types based on statistical t tests. Finite-fault energy estimations also support focal mechanism dependence of apparent stress but only for shallow earthquakes (Z < 30 km). The slip distribution population used was too small to conclude that finite-fault energy estimations support the dependence of average apparent stress on rupture type at different depth intervals.

Earth System Science Data, 2023

We present a focal mechanism catalog for earthquakes that occurred in Mexico and surrounding area... more We present a focal mechanism catalog for earthquakes that occurred in Mexico and surrounding areas reported from February 1928 to July 2022. The magnitude of the events varies from −0.9 to 8.2. The hypocentral depth is in the range of 0 < Z < 270 km. Focal mechanisms in this catalog are associated with tectonic, geothermal, and volcanic environments. Reported focal mechanisms were derived using different types of data at local, regional, and teleseismic distances and different methods such as first motions, composite solutions, waveform analysis, and moment tensor inversion. So far, focal mechanism data for earthquakes in Mexico are dispersed over many publications without any link among them. For this reason, we collect and revise focal mechanism solutions previously reported by different agencies and studies from published sources. Our catalog consists of 7664 focal mechanism solutions for a total of 5701 events since we report all the available focal mechanisms obtained by different authors and seismological agencies for each seismic event. Additionally, we classify the focal mechanisms according to their fault types using the ternary diagrams of Kaverina-type classification. We also rank the quality of the focal mechanism data into three categories: A, B, and C. A represents good/reliable data, B represents satisfactory data, and C represents poor/questionable data according to well-defined criteria. The main goal of this study is to provide a comprehensive compilation of focal mechanism data that can help in future source and tectonic studies in Mexico.

Geophysical Research Letters, 2003

Earth Surface Processes and Landforms, 2010

... Recent tectonic activity within the central-eastern TMVB is represented by east-west (EW) str... more ... Recent tectonic activity within the central-eastern TMVB is represented by east-west (EW) strikingnormal and trans-tensional faults that define a 50 ... Suter et al., 1992, 1995a, 1995b, 1996, 2001; Ramírez-Herrera, 1998; Langridge et al., 2000; Szynkaruk et al., 2004; Norini et al ...

Bulletin of the New Zealand Society for Earthquake Engineering, 2005

The authors have analyzed the main temporal characteristics of the earthquake data in the catalog... more The authors have analyzed the main temporal characteristics of the earthquake data in the catalogue of seismicity of New Zealand with the objective of providing a general overview of its content and limitations. To this end we have employed different statistical tools which allow for the objective estimate of times of changes in the seismicity rates as well as providing the main reasons for those changes. We have found that the seismicity record of the largest events (M > 4.0) is bracketed by significant changes which occurred during 1940, 1965-1968, and 1987 with other less significant changes taking place during 1960, 1983 and 1992. By comparing the rates obtained for intervals bounded by the aforementioned dates we were able to determine that a linear correction to the magnitudes in the period 1968 to 1987 for the whole depth range of events may be useful in order to match the frequency-magnitude distribution which is obtained using the current data in the interval 1987 - 2004...

This study focuses on the identification and seismic characterization of the San Mateo fault, her... more This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1–6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 5.32 ky. A slip rate of 0.085 0.025 mm / year and a magnitude (Mw) of 6.43 to 6.76 is estimated from the maximum coseismic dis...

Bulletin of the Seismological Society of America, 2001

Bulletin of the Seismological Society of America, 2012

ABSTRACT The problem of converting from one magnitude scale to another is revisited in light of a... more ABSTRACT The problem of converting from one magnitude scale to another is revisited in light of a method that preserves the b‐value of the Gutenberg–Richter (GR) law of one of the two magnitude distributions. This methodology allows for the use of all reliable magnitude data rather than data of only those events for which paired magnitudes are available. Our method avoids resolving incompatible magnitude ranges. The temporal stability of a‐and b‐values and of the resulting linear relation coefficients is considered as a basis for selecting an ...

We have looked into the interevent time distribution of aftershock sequences from different tecto... more We have looked into the interevent time distribution of aftershock sequences from different tectonic regimes with the aim of gaining information on the aftershock process. To this end we looked at some well defined aftershock sequences from Alaska, New Zealand and Mexico and proceeded to identify the distribution patterns of interevent times (also called waiting times) in both time and space. Several results emanate from this exercise. In most cases, more than one coherent process can be discerned with those acting following the main process, occurring surprisingly not in the volume surrounding the main rupture volume but rather within it.

vi 4.1. Gráficas de la variabilidad temporal de los valores b, a y M c para la región SUB1. a) Es... more vi 4.1. Gráficas de la variabilidad temporal de los valores b, a y M c para la región SUB1. a) Estimación de M c mediante el método MAXC. b) Estimación de M c mediante el método MC. La línea continua roja representa el periodo estable del valor b.

The b value of the Gutenberg-Richter relationship is at the center of most seismic risk estimates... more The b value of the Gutenberg-Richter relationship is at the center of most seismic risk estimates, and has demonstrated its value in research focusing on seismicity or stress conditions. The estimate of this value depends on several factors, among which we can mention the homogeneity of magnitudes, the correct quantification of the minimum magnitude of completeness, the accuracy of the locations (especially in the case of local studies), the rate of seismicity, the installation and density of monitoring stations, etc.. However, a factor that has not been taken into account with the importance it deserves is the temporal stability of the estimation of b-values. A common procedure to obtain a b-value estimate is by compiling all available seismicity which is deemed suitable for an area of interest and calculate an estimate normalized per unit time. Clearly, if there are no anomalous siesmicity outbursts, as we progress in time, the b-value should remain stable even if we add more data...

The spatial distribution of the b value under volcanoes and other tectonic environments is not un... more The spatial distribution of the b value under volcanoes and other tectonic environments is not uniform but it rather shows pockets of anomalies related to different phenomena. We analyzed the frequency-magnitude distribution of the 2191 best located volcano-tectonic events with MD ≥ 2.1 under the Popocatepetl volcano and performed 2D and 3D maps using a griding technique. For the 3D mapping we used samples of 100 events within spherical volumes with radii ≤ 3 km. Also, only volumes with σ ≤ 0.3 were taken into account. Three main anomalies with b ≥ 2.2 were detected within a normal crust (b ≤ 1.6). The first anomaly is observed north of the crater summit at depths 4-8 km and comprises a volume of approximately 15 km3. The second lies slightly to the E and SE of the crater at depths between 2 and 5 km, and the third and latter anomaly is located SE of the summit at depths of 6-12 km and spans over a volume of 40 km3 (or greater). In any case, we interpret our high b values anomalies ...

Solid Earth, 2024

We derived scaling relationships for different seismic energy metrics for earthquakes around the ... more We derived scaling relationships for different seismic energy metrics for earthquakes around the globe with MW > 6.0 from 1990 to 2022. The seismic energy estimations were derived with two methodologies, the first based on the velocity flux integration and the second based on finite-fault models. In the first case, we analyzed 3331 reported seismic energies derived by integrating far-field waveforms. In the latter methodology, we used the total moment rate functions and the approximation of the overdamped dynamics to quantify seismic energy from 231 finite-fault models (Emrt and EO, EU, respectively). Both methodologies provide compatible energy estimates. The radiated seismic energies estimated from the slip models and integration of velocity records are also compared for different types of focal mechanisms (R, reverse; R-SS, reverse–strike-slip; SS, strike-slip; SS-R, strike-slip–reverse; SS-N, strike-slip–normal; N, normal; and N-SS, normal–strike-slip), and then used to derive converting scaling relations among the different energy types. Additionally, the behavior of radiated seismic energy (ER), energy-to-moment ratio (), and apparent stress (τα) for different rupture types at a global scale is examined by considering depth variations in mechanical properties, such as seismic velocities, rock densities, and rigidities. For this purpose, we used a 1-D global velocity model. The ratio is, based on statistical t tests, largest for strike-slip earthquakes, followed by normal-faulting events, with the lowest values for reverse earthquakes for hypocentral depths < 90 km. Not enough data are available for statistical tests at deeper intervals except for the 90 to 120 km range, where we can satisfactorily conclude that for R-SS and SS-R types is larger than for N-type faulting, which also conforms to the previous assumption. In agreement with previous studies, our results exhibit a robust variation in τα with the focal mechanism. Regarding the behavior of τα with depth, our results agree with the existence of a bimodal distribution with two depth intervals where the apparent stress is maximum for normal-faulting earthquakes. At depths in the range of 180–240 km, τα for reverse earthquakes is higher than for normal-faulting events. We find the trend EU > Emrt > EO for all mechanism types based on statistical t tests. Finite-fault energy estimations also support focal mechanism dependence of apparent stress but only for shallow earthquakes (Z < 30 km). The slip distribution population used was too small to conclude that finite-fault energy estimations support the dependence of average apparent stress on rupture type at different depth intervals.

Earth System Science Data, 2023

We present a focal mechanism catalog for earthquakes that occurred in Mexico and surrounding area... more We present a focal mechanism catalog for earthquakes that occurred in Mexico and surrounding areas reported from February 1928 to July 2022. The magnitude of the events varies from −0.9 to 8.2. The hypocentral depth is in the range of 0 < Z < 270 km. Focal mechanisms in this catalog are associated with tectonic, geothermal, and volcanic environments. Reported focal mechanisms were derived using different types of data at local, regional, and teleseismic distances and different methods such as first motions, composite solutions, waveform analysis, and moment tensor inversion. So far, focal mechanism data for earthquakes in Mexico are dispersed over many publications without any link among them. For this reason, we collect and revise focal mechanism solutions previously reported by different agencies and studies from published sources. Our catalog consists of 7664 focal mechanism solutions for a total of 5701 events since we report all the available focal mechanisms obtained by different authors and seismological agencies for each seismic event. Additionally, we classify the focal mechanisms according to their fault types using the ternary diagrams of Kaverina-type classification. We also rank the quality of the focal mechanism data into three categories: A, B, and C. A represents good/reliable data, B represents satisfactory data, and C represents poor/questionable data according to well-defined criteria. The main goal of this study is to provide a comprehensive compilation of focal mechanism data that can help in future source and tectonic studies in Mexico.

Geophysical Research Letters, 2003

Earth Surface Processes and Landforms, 2010

... Recent tectonic activity within the central-eastern TMVB is represented by east-west (EW) str... more ... Recent tectonic activity within the central-eastern TMVB is represented by east-west (EW) strikingnormal and trans-tensional faults that define a 50 ... Suter et al., 1992, 1995a, 1995b, 1996, 2001; Ramírez-Herrera, 1998; Langridge et al., 2000; Szynkaruk et al., 2004; Norini et al ...

Bulletin of the New Zealand Society for Earthquake Engineering, 2005

The authors have analyzed the main temporal characteristics of the earthquake data in the catalog... more The authors have analyzed the main temporal characteristics of the earthquake data in the catalogue of seismicity of New Zealand with the objective of providing a general overview of its content and limitations. To this end we have employed different statistical tools which allow for the objective estimate of times of changes in the seismicity rates as well as providing the main reasons for those changes. We have found that the seismicity record of the largest events (M > 4.0) is bracketed by significant changes which occurred during 1940, 1965-1968, and 1987 with other less significant changes taking place during 1960, 1983 and 1992. By comparing the rates obtained for intervals bounded by the aforementioned dates we were able to determine that a linear correction to the magnitudes in the period 1968 to 1987 for the whole depth range of events may be useful in order to match the frequency-magnitude distribution which is obtained using the current data in the interval 1987 - 2004...

This study focuses on the identification and seismic characterization of the San Mateo fault, her... more This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1–6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 5.32 ky. A slip rate of 0.085 0.025 mm / year and a magnitude (Mw) of 6.43 to 6.76 is estimated from the maximum coseismic dis...

Bulletin of the Seismological Society of America, 2001

Bulletin of the Seismological Society of America, 2012

ABSTRACT The problem of converting from one magnitude scale to another is revisited in light of a... more ABSTRACT The problem of converting from one magnitude scale to another is revisited in light of a method that preserves the b‐value of the Gutenberg–Richter (GR) law of one of the two magnitude distributions. This methodology allows for the use of all reliable magnitude data rather than data of only those events for which paired magnitudes are available. Our method avoids resolving incompatible magnitude ranges. The temporal stability of a‐and b‐values and of the resulting linear relation coefficients is considered as a basis for selecting an ...

We have looked into the interevent time distribution of aftershock sequences from different tecto... more We have looked into the interevent time distribution of aftershock sequences from different tectonic regimes with the aim of gaining information on the aftershock process. To this end we looked at some well defined aftershock sequences from Alaska, New Zealand and Mexico and proceeded to identify the distribution patterns of interevent times (also called waiting times) in both time and space. Several results emanate from this exercise. In most cases, more than one coherent process can be discerned with those acting following the main process, occurring surprisingly not in the volume surrounding the main rupture volume but rather within it.

vi 4.1. Gráficas de la variabilidad temporal de los valores b, a y M c para la región SUB1. a) Es... more vi 4.1. Gráficas de la variabilidad temporal de los valores b, a y M c para la región SUB1. a) Estimación de M c mediante el método MAXC. b) Estimación de M c mediante el método MC. La línea continua roja representa el periodo estable del valor b.

The b value of the Gutenberg-Richter relationship is at the center of most seismic risk estimates... more The b value of the Gutenberg-Richter relationship is at the center of most seismic risk estimates, and has demonstrated its value in research focusing on seismicity or stress conditions. The estimate of this value depends on several factors, among which we can mention the homogeneity of magnitudes, the correct quantification of the minimum magnitude of completeness, the accuracy of the locations (especially in the case of local studies), the rate of seismicity, the installation and density of monitoring stations, etc.. However, a factor that has not been taken into account with the importance it deserves is the temporal stability of the estimation of b-values. A common procedure to obtain a b-value estimate is by compiling all available seismicity which is deemed suitable for an area of interest and calculate an estimate normalized per unit time. Clearly, if there are no anomalous siesmicity outbursts, as we progress in time, the b-value should remain stable even if we add more data...

The spatial distribution of the b value under volcanoes and other tectonic environments is not un... more The spatial distribution of the b value under volcanoes and other tectonic environments is not uniform but it rather shows pockets of anomalies related to different phenomena. We analyzed the frequency-magnitude distribution of the 2191 best located volcano-tectonic events with MD ≥ 2.1 under the Popocatepetl volcano and performed 2D and 3D maps using a griding technique. For the 3D mapping we used samples of 100 events within spherical volumes with radii ≤ 3 km. Also, only volumes with σ ≤ 0.3 were taken into account. Three main anomalies with b ≥ 2.2 were detected within a normal crust (b ≤ 1.6). The first anomaly is observed north of the crater summit at depths 4-8 km and comprises a volume of approximately 15 km3. The second lies slightly to the E and SE of the crater at depths between 2 and 5 km, and the third and latter anomaly is located SE of the summit at depths of 6-12 km and spans over a volume of 40 km3 (or greater). In any case, we interpret our high b values anomalies ...

TESIS Maestría. Posgrado en Ciencias de la Tierra UNAM, 2013

La posibilidad de pronosticar la ocurrencia de eventos s smicos es sin duda uno de los más grande... more La posibilidad de pronosticar la ocurrencia de eventos s smicos es sin duda uno de los más grandes retos de la sismología, pero por la limitada cantidad de información resulta difícil lograr este cometido.
La mayor a de los estudios de sismología se han enfocado en el conocimiento y comprensión del mecanismo físico que genera los terremotos, para posteriormente evaluar el daño que podría ocasionar cada evento en zonas particulares. Sin embargo, conforme aumenta el conocimiento, se ha observado que existen procesos que no pueden ser
explicados de forma determinista mediante un teoría física, como lo es la recurrencia sísmica. El hecho de contar con poco tiempo de información y no comprender con certeza el comportamiento e interacción de todas las variables involucradas en el fenómeno, conlleva a proponer que éstas se rigen por medio de un proceso desconocido y por lo tanto aleatorio. En este caso, se plantea tratar el proceso mediante un modelo estocástico.
La idea de modelar fenómenos naturales mediantes procesos aleatorios no significa que se trata al problema de forma azarosa. De hecho, la principal razón de considerar modelos estocásticos es hacer explícitas las incertidumbres, información de la cual carecen los modelos deterministas.
Los avances en el procesamiento computacional son una poderosa herramienta para tratar fenómenos mediante procesos aleatorios. Se ha demostrado que los problemas complejos que no pueden ser resueltos de forma determinista, como por ejemplo una optimización global de alguna función no lineal, puede ser tratada mediante procesos aleatorios. El método Montecarlo fue el primero en ser utilizado para solucionar
problemas de esta magnitud con precisión y en un tiempo de cómputo razonable.
Posteriormente, se han ido desarrollando metodologías cada vez más sofisticadas que involucran procesos aleatorios inspirados en el comportamiento de las especies u otro procesos natural, que agilizan el tiempo de procesamiento y la calidad de la solución. Por
ejemplo, las redes neuronales artificiales y los algoritmos evolutivos.
En este trabajo se estudia la probabilidad de que ocurra un evento significativo en la zona de subducción mexicana, tratando al fenómeno mediante un modelo estocástico.
Este modelo considera la ocurrencia de eventos de en segmentos adyacentes como procesos independientes, con los cuales se construyen distribuciones de probabilidad adecuadas que describan la ocurrencia de eventos en el tiempo mediante simulaciones Montecarlo. Posteriormente, las distribuciones de probabilidades correspondientes a cada segmento permitir n identificar la concatenación de rupturas adyacentes (sismos lo suficientemente cercanos en espacio y tiempo). Además, se utiliza
un algoritmo evolutivo para estimar de forma inversa el tiempo interevento de concatenaciones de segmentos, lo cual es relevante en este trabajo.