Seismicity Rate Changes Research Articles

Putting faults in the northern Chilean subduction margin into motion: evidence for remote dynamic earthquake triggering on the plate interface and within the forearc

Dynamic stresses on the order of ~1 kPa from passing waves of mainshock earthquakes can trigger aftershocks at remote distances. Here, we investigate the prevalence of remote earthquake triggering in northern Chile, where aseismic-slip triggering has been documented. Our twofold approach to quantify triggerability includes a statistical difference-of-means test to quantify seismicity-rate changes bracketing candidate mainshock times, and a waveform-based approach to look for triggered earthquakes missing from the local catalog. We find no persistent, statistically-significant seismicity-rate increases associated with any of the candidate mainshocks when considering the local catalog in aggregate. However, catalog statistics reveal evidence for localized triggering both on the subduction interface and within the shallower forearc faults. Waveforms reveal local, uncataloged earthquakes only visible using a high-pass filter that removes the mainshock signal that otherwise overprints the local signals. Based on Japan mainshocks, we cannot rule out antipodal triggering. Areas showing higher triggerability are consistent with regions of low locking inferred from GNSS models and regions of observed aseismic slip. The spatial coincidence of triggering and low-locking, combined with the absence of a stress-triggering threshold, requires non-linear triggering mechanisms, such as altered frictional strength or aseismic-slip triggering, to be consistent with the observations.

Constraining Parameter Uncertainties in the Coulomb Rate–State Approach: A Case Study of Seismicity in the Longmenshan Region after the 2008 Mw 7.9 Wenchuan Earthquake, China

Abstract The rate–state frictional law, coupled with the Coulomb failure stress changes (ΔCFS), is one of the most popular physics-based models to forecast seismicity rate changes following a major earthquake. However, its effectiveness is hampered by parameter uncertainties. To seek possible solutions for such uncertainties, this article carried out retrospective forecasts of the decade-long seismicity in the Longmenshan region, China, after the 2008 Mw 7.9 Wenchuan earthquake, and proposed methods to constrain parameter uncertainties. First, we derived spatially variable ta and Aσ from fault-slip rates. This method not only provides observational constraints for these two parameters but also reflects spatial variations of fault rate–state properties. Second, although both complete and declustered background catalogs are common in Coulomb rate–state forecasts, this study demonstrated that declustering avoids false alerts of seismicity rate increase that resulted from temporary seismicity fluctuations in the background catalog. Finally, we extended the model from its typical application based on a stress step (the coseismic stress change) to a calculation that allows a more complex stress evolution (the postseismic viscoelastic stress change). With these methods to constrain parameter uncertainties, we are able to obtain more reliable forecasts.

The 2022–2023 seismic sequence onshore South Evia, central Greece: evidence for activation of a left-lateral strike-slip fault and regional triggering of seismicity

On 29 November 2022, an earthquake of ML 5.0 (Mw 4.8) occurred onshore South Evia Island (central Greece) preceded by a ML 4.7 (Mw 4.6) event. The pattern of relocated aftershocks indicates the activation of a single, near-vertical fault segment, oriented NW-SE at shallow crustal depths (6–11 km). We suggest that both events ruptured a blind, left-lateral strike-slip fault, about 5 km southeast of village Almyropotamos. We observed that a clear foreshock activity (N=55 events) existed before the two moderate events. The impact of the static stress loading on neighboring fault planes diminishes after a distance of 7 km from the November 2022 epicenters, where the static stress falls below +0.1 bar. We further explore triggering relationships between the 29 November events and the late December 2022 moderate events (ML 4.9) that occurred about 60 km toward NW in the Psachna and Vlahia regions of central Evia. We present evidence of possible delayed dynamic triggering of the late December 2022 central Evia sequence, based on marked changes in seismicity rates and on measured peak ground velocities (PGVs) and peak dynamic strains, both exhibiting local maxima in their map distributions. The causes of the delayed triggering may be related to the well-known geothermal field in central/north Evia and the NW-SE strike of the seismic fault.

Induced seismicity in the Changning salt mining zone, China, could be driven by the pore-pressure diffusion

The detailed mechanism of induced seismicity associated with salt mining remains elusive. Herein we compile the geological, industrial data, and seismic records within the Changning salt mining zone, China, and simulate the changes in crustal stresses and seismicity rate based on the physics-based poroelastic model and rate-and-state earthquake nucleation model. Our models reveal that the regional induced seismicity, including the 2019 Ms. 6.0 Changning earthquake, which might be one of the largest induced events by industrial exploitation ever recorded, is mainly driven by the pore-pressure diffusion, but suppressed by pumping operations. Motivated by the injection-extraction scenario, we further investigate the effect of wells' locations on stress changes, which could be potentially used for well site optimization to minimize the poroelastic response. A simple mode of setting extraction wells around the injection well could reduce the seismicity rate by a factor of two. These results collectively advance the understanding of physics and hazards associated with injection-extraction-induced earthquakes, and help design or guide industrial well deployment.

Physics-informed deep learning to forecast {widehat{{varvec{M}}}}_{{varvec{m}}{varvec{a}}{varvec{x}}} during hydraulic fracturing

Short-term forecasting of estimated maximum magnitude ({widehat{M}}_{max}) is crucial to mitigate risks of induced seismicity during fluid stimulation. Most previous methods require real-time injection data, which are not always available. This study proposes two deep learning (DL) approaches, along with two data-partitioning methods, that rely solely on preceding patterns of seismicity. The first approach forecasts {widehat{M}}_{max} directly using DL; the second incorporates physical constraints by using DL to forecast seismicity rate, which is then used to estimate {widehat{M}}_{max}. These approaches are tested using a hydraulic-fracture monitoring dataset from western Canada. We find that direct DL learns from previous seismicity patterns to provide an accurate forecast, albeit with a time lag that limits its practical utility. The physics-informed approach accurately forecasts changes in seismicity rate, but sometimes under- (or over-) estimates {widehat{M}}_{max}. We propose that significant exceedance of {widehat{M}}_{max} may herald the onset of runaway fault rupture.

Relative Afterslip Moment Does Not Correlate With Aftershock Productivity: Implications for the Relationship Between Afterslip and Aftershocks

AbstractAseismic afterslip has been proposed to drive aftershock sequences. Both afterslip moment and aftershock number broadly increase with mainshock size, but can vary beyond this scaling. We examine whether relative afterslip moment (afterslip moment/mainshock moment) correlates with several key aftershock sequence characteristics, including aftershock number and cumulative moment (both absolute and relative to mainshock size), seismicity rate change, b‐value, and Omori decay exponent. We select Mw ≥ 4.5 aftershocks for 41 tectonically varied mainshocks with available afterslip models. Against expectation, relative afterslip moment does not correlate with tested aftershock characteristics or background seismicity rate. Furthermore, adding afterslip moment to mainshock moment does not improve predictions of aftershock number. Our findings place useful empirical constraints on the link between afterslip and potentially damaging Mw ≥ 4.5 aftershocks and raise questions regarding the role afterslip plays in aftershock generation.

A High-Resolution Earthquake Catalog for the 2004 Mw 6 Parkfield Earthquake Sequence Using a Matched Filter Technique

Abstract We present the high-resolution Parkfield matched filter relocated earthquake (PKD-MR) catalog for the 2004 Mw 6 Parkfield earthquake sequence in central California. We use high-quality seismic data recorded by the borehole High Resolution Seismic Network combined with matched filter detection and relocations from cross-correlation derived differential travel times. We determine the magnitudes of newly detected events by computing the amplitude ratio between the detections and templates using a principal component fit. The relocated catalog spans from 6 November 2003 to 28 March 2005 and contains 13,914 earthquakes, which is about three times the number of events listed in the Northern California Seismic Network catalog. Our results on the seismicity rate changes before the 2004 mainshock do not show clear precursory signals, although we find an increase in the seismic activity in the creeping section of the San Andreas fault (SAF) (about ∼30 km northwest of the mainshock epicenter) in the weeks prior to the mainshock. We also observe a decrease in the b-value parameter in the Gutenberg–Richter relationship in the creeping section in the weeks prior to the mainshock. Our results suggest stress is increasingly released seismically in the creeping section, accompanied by a decreasing aseismic creeping rate before the mainshock occurrence. However, b-value and seismicity rates remain stable in the Parkfield section where the 2004 mainshock ruptured. This updated catalog can be used to study the evolution of aftershocks and their relations to afterslip following the 2004 Parkfield mainshock, seismicity before the mainshock, and how external stresses interact with the Parkfield section of the SAF and the 2004 sequence.

Temporal changes of seismicity in Salton Sea Geothermal Field due to distant earthquakes and geothermal productions

SUMMARY The Salton Sea Geothermal Field (SSGF) is one of the most seismically active and geothermally productive fields in California. Here we present a detailed analysis of short-term seismicity change in SSGF from 2008 to 2013 during and right following large distant earthquakes, as well as long-term seismicity change due to geothermal productions. We first apply a GPU-based waveform matched-filter technique (WMFT) to the continuous data recorded by the Calenergy Borehole (EN) Network and detect more than 70 000 new micro-earthquakes than listed in the standard Southern California Seismic Network catalogue. We then analyse the seismicity rate changes in the SSGF associated with transient stress fluctuations triggered by regional and large teleseismic earthquakes from 1999 to 2019. We find triggered seismicity in the SSGF following seven regional M > 5.5 earthquakes. In comparison, most teleseismic earthquakes with M > 8.0 did not trigger significant seismicity rate change in the SSGF, likely indicating a frequency dependence in remote dynamic triggering. We further characterize the correlation between the long-term seismicity rate and geothermal production rates, and the temporal and spatial distribution of Guttenberg–Richter b-values inside and outside the SSGF with the newly detected catalogue. The long-term seismicity shows that events with M > 1.5 are likely correlated with net production rates, while smaller events do not show any correlation. The b-values inside the SSGF are higher than those outside the SSGF, and the locations of dynamically triggered events are close to locations with high b-values.

Identifying plausible historical scenarios for coupled lake level and seismicity rate changes: the case for the Dead Sea during the last 2 millennia

Abstract. Studies of seismicity induced by water level changes in reservoirs and lakes focus typically on well-documented contemporary records. Can such interactions be explored on a historical timescale when the two data types suffer from severe uncertainties stemming from the different nature of the data, methods and resolution? In this study, we show a way to considerably improve the correlation between interpolated records of historical Dead Sea level reconstructions and discrete seismicity patterns in the area, over the period of the past 2 millennia. Inspired by the results of our previous study, we carefully revise the historical earthquake catalog in the Dead Sea to exclude remote earthquakes and include small local events. For addressing the uncertainties in lake levels, we generate an ensemble of random interpolations of water level curves and rank them by correlation with the historical records of seismic stress release. We compute a synthetic catalog of earthquakes, applying a Mohr–Coulomb failure criterion. The critical state of stress at hypocentral depths is achieved by static poroelastic deformations incorporating the change in effective normal stress (due to the best-fit water level curve) superimposed on the regional strike-slip tectonic deformations. The earthquakes of this synthetic catalog show an impressive agreement with historical earthquakes documented to have damaged Jerusalem. We refine the seismic catalog by searching for small local events that toppled houses in Jerusalem; including all local events improves the correlation with lake levels. We demonstrate for the first time a high correlation between water level changes and the recorded recurrence intervals of historical earthquakes.

Forecasting induced seismicity in Oklahoma using machine learning methods

Oklahoma earthquakes in the past decade have been mostly associated with wastewater injection. Here we use a machine learning technique—the Random Forest to forecast induced seismicity rate in Oklahoma based on injection-related parameters. We split the data into training (2011.01–2015.05) and test (2015.06–2020.12) periods. The model forecasts seismicity rate during the test period based on input features, including operational parameters (injection rate and pressure), geological information (depth to basement), and modeled pore pressure and poroelastic stress. The results show overall good match with observed seismicity rate (adjusted R^2 of 0.75). The model shows that pore pressure rate and poroelastic stressing rates are the two most important features in forecasting. The absolute values of pore pressure and poroelastic stress, and the injection rate itself, are less important than the stressing rates. These findings further emphasize that temporal changes of stressing rates would lead to significant changes in seismicity rates.

Coulomb stress changes due to the 2021 MS7.4 Maduo Earthquake and expected seismicity rate changes in the surroundings

Coulomb stress changes due to the 2021 MS7.4 Maduo Earthquake and expected seismicity rate changes in the surroundings

Changepoint detection in seismic double-difference data: application of a trans-dimensional algorithm to data-space exploration

Abstract. Double-difference (DD) seismic data are widely used to define elasticity distribution in the Earth's interior and its variation in time. DD data are often pre-processed from earthquake recordings through expert opinion, whereby pairs of earthquakes are selected based on some user-defined criteria and DD data are computed from the selected pairs. We develop a novel methodology for preparing DD seismic data based on a trans-dimensional algorithm, without imposing pre-defined criteria on the selection of event pairs. We apply it to a seismic database recorded on the flank of Katla volcano (Iceland), where elasticity variations in time have been indicated. Our approach quantitatively defines the presence of changepoints that separate the seismic events in time windows. Within each time window, the DD data are consistent with the hypothesis of time-invariant elasticity in the subsurface, and DD data can be safely used in subsequent analysis. Due to the parsimonious behaviour of the trans-dimensional algorithm, only changepoints supported by the data are retrieved. Our results indicate the following: (a) retrieved changepoints are consistent with first-order variations in the data (i.e. most striking changes in the amplitude of DD data are correctly reproduced in the changepoint distribution in time); (b) changepoint locations in time correlate neither with changes in seismicity rate nor with changes in waveform similarity (measured through the cross-correlation coefficients); and (c) the changepoint distribution in time seems to be insensitive to variations in the seismic network geometry during the experiment. Our results demonstrate that trans-dimensional algorithms can be effectively applied to pre-processing of geophysical data before the application of standard routines (e.g. before using them to solve standard geophysical inverse problems).

Can Hydrocarbon Extraction From the Crust Enhance or Inhibit Seismicity in Tectonically Active Regions? A Statistical Study in Italy

A number of oil- and gas-producing leases have been operating in Italy in the last decades, many of which are located in the surroundings of tectonically active regions. Identifying human-induced seismicity in areas with high levels of natural seismicity is a difficult task for which virtually any result can be a source of controversy. We implemented a large-scale analysis aiming at tracking significant departures of background seismicity from a stationary behavior around active oil and gas development leases in Italy. We analyzed seismicity rates before and after hydrocarbon peak production in six oil-producing and 43 gas-producing leases, and evaluate the significance of possible seismicity rate changes. In a considerable number of cases seismicity rate results stationary. None of the observed cases of seismicity rate increase after the peak production is statistically significant (at as.l.= 0.05). Conversely, considering cases of seismicity rate decrease after peak production, our results suggest that the seismicity rate reduction is statistically significant (s.l.= 0.05) around one oil-producing lease (Val d’Agri, Basilicata) and around a cluster of gas-producing leases in Sicily. Our results put in evidence correlated changes between the rates of shallow seismicity and hydrocarbon production in these areas, which are then identified as hotspots requiring more detailed research; assessing actual causal relationships between these processes will require further physically-based modelling. If a physical causative link between these processes exists, then the observed seismicity rate reduction could either be due to increased seismicity during the progressive increase in production before reaching its maximum, or to an actual seismicity rate reduction after that peak. Considering that there is evidence of seismicity occurring before the start of hydrocarbon production, which contrasts with the evident reduction of events observed after the peak production, we think it likely that the seismicity inhibition is a plausible hypothesis. Using a simple model we also calculate Coulomb stress changes in planes optimally oriented for failure, and we show that under some conditions the inhibition of seismicity is feasible in at least one of these cases. We conclude that more efforts to study the mechanisms and the possible consequences of anthropogenically-driven seismicity inhibition are required.

Seismicity Rate Change as a Tool to Investigate Delayed and Remote Triggering of the 2010–2011 Canterbury Earthquake Sequence, New Zealand

ABSTRACTCrustal earthquakes in low-strain-rate regions are rare in the human life span but can generate disastrous consequences when they occur. Such was the case in the Canterbury earthquake sequence that began in 2010 and eventually led to almost 200 fatalities. Our study explores this earthquake sequence’s origins by producing an enhanced earthquake catalog in the Canterbury Plains and Otago, South Island, New Zealand. We investigate seismicity rate changes from 2005 to before the 2010 Mw 7.2 Darfield earthquake. During this time, major subduction-zone earthquakes, such as the 2009 Mw 7.8 Dusky Sound earthquake, created measurable coseismic and postseismic strain in the region. We use template matching to expand the catalog of earthquakes in the region, and use a support vector machine classifier to remove false positives and poor detections. We then compare the newly obtained seismicity rates with the coseismic and postseismic crustal strain fields, and find that seismicity rate and crustal strain are positively correlated in the low-stress, low-seismicity region of the northern Canterbury Plains. In contrast, near fast-moving plate-boundary faults, the seismicity rate changes rise without much change in the strain rate. Our analysis reveals a substantial seismicity rate decrease in the western rupture area of the Darfield earthquake, which we infer to be an effect of coseismic and postseismic deformation caused by the Dusky Sound earthquake. We show in low-strain-rate regions, stress perturbation of a few kPas creates substantial seismicity rate change. However, the implication that such seismic quiescence is responsible for the nucleation of the Darfield earthquake requires further studies.

Dynamic Earthquake Triggering in Southern California in High Resolution: Intensity, Time Decay, and Regional Variability

AbstractEarthquake triggering by seismic waves has been recognized as a phenomenon for nearly 30 years. However, our ability to study dynamic triggering has been limited by our ability to capture the triggering stresses accurately and record the resultant earthquakes. Here we use full waveforms from a dense seismic network and a modern, high‐resolution seismic catalog to measure triggering in Southern California from 2008 to 2017 based on interevent time ratios. We find that the fractional seismicity rate change, which we term triggering intensity or triggerability, as a function of peak strain change for the period of ∼20 s due to distant earthquakes is monotonically increasing and compatible with earlier measurements made with a disjoint data set from 1984 to 2008. A triggering strain of 1 microstrain is equivalent to the local productivity generated by an M1.8 earthquakes. This result implies that a prediction of seismicity rate changes can be made based on recorded ground shaking using the same formalism as currently used for aftershock prediction. For a teleseismic event, this small level of triggering occurs throughout the region and thus aggregates to a regional effect. We find that the triggering rate decays after the triggerer follows an Omori‐Utsu law, but at a much slower rate than a typical aftershock sequence. The slow decay rate suggests that an ancillary process such as creep or fluid flow must be part of dynamic triggering. The prevalence of triggering in areas of creep or fluid involvement reinforces this inference. A triggering cascade of secondary earthquakes is insufficient to explain the data.

A Decade of Global Navigation Satellite System/Acoustic Measurements of Back-Arc Spreading in the Southwestern Okinawa Trough

Long-term seafloor geodetic measurements are important for constraining submarine crustal deformation near plate boundaries. Here we present an integrated analysis of a decade of GNSS/acoustic data collected at a site 60 km to the east of northeast Taiwan near the axis of the Okinawa Trough back-arc basin. We obtained a time-series of horizontal and vertical positions based on 18 measurements from 2009 to 2019. These data reveal a southeastward movement at a rate of 43 ± 5 mm/yr since 2012 with respect to the Yangtze Plate. The horizontal motion can be explained by the clockwise rotation of the Yonaguni Block and northern Central Range. In addition, the vertical displacement of the transponder array shows rapid subsidence of 22 ± 9 mm/yr from 2012 to 2019. The fast subsidence rate and negative free-air gravity anomaly in this region indicate that crustal thinning is compensated mainly by surface deformation rather than upward migration of the Moho. Taking into account the offset in 2012 owing to the replacement of the transponder array, the horizontal position time series of our site are best explained by two linear lines with a slope change in July 2013. The timing of the velocity change coincides broadly with a change in the nearby seismicity rate and dike intrusion 150 km away from the site. Our results highlight the potential of seafloor geodesy in assessing temporal changes in deformation near the spreading center of the Okinawa Trough, which cannot be one using data from onland GNSS stations.

Dynamic triggering of earthquakes in the North Island of New Zealand following the 2016 Mw 7.8 Kaikōura earthquake

Large earthquakes are capable of triggering microseismicity, deep tremor and slow-slip events from intermediate- to long-distance ranges. Unfortunately, earthquake catalogs are typically incomplete right after large mainshocks. Hence, mapping triggering patterns and understanding the underlying triggering mechanism are challenging. Here we present two different types of seismicity responses to dynamic stressing by passing seismic waves in the North Island of New Zealand following the 2016 Mw 7.8 Kaikōura earthquake. Based on a template matching technique, we identify up to 4-7 times more earthquakes than listed in New Zealand's GeoNet catalog. We also compute the dynamic stress perturbations in the North Island due to the Kaikōura mainshock and compare them to seismicity rate changes to identify regions with high susceptibility to dynamic stress triggering. Abundant triggered earthquakes occurred immediately following the mainshock in the shallow crust around the active Taupo Volcano Zone, likely related to activation of crustal faults/fluids associated with back-arc rifting and volcanism. Approximately 8 days after the initial dynamic stressing, an active burst of seismicity with the largest event of ML 5.55 occurred along the shallow megathrust near Porangahau on the east coast of the North Island. This burst of seismicity is likely driven by a ∼Mw 7.1 shallow slow slip event dynamically triggered by the mainshock. Our findings reveal the heterogeneous nature of dynamic triggering in a plate boundary region with recent large earthquake sequences and aseismic transient events and further highlight the difficulties in time-dependent earthquake forecasting following large mainshocks.

Stress and pore fluid pressure control of seismicity rate changes following the 2016 Kumamoto earthquake, Japan

We quantitatively examined the influence of pore fluid pressure and coseismic stress changes on the seismicity rate changes that followed the 2016 Kumamoto earthquake, on the basis of two approaches. One is a numerical calculation of the classic stress metric of ∆CFS, and the other is an inversion analysis of pore fluid pressure fields with earthquake focal mechanism data. The former calculation demonstrated that seismicity rate changes were consistent with the expectation from ∆CFS in 65% of the target region, whereas they were not in the remaining 35% of the region. The latter analysis indicates that seismicity rates increased in the regions where pore fluid pressure before the Kumamoto earthquake sequence was remarkably enhanced above hydrostatic, regardless of values of ΔCFS. This suggests that the increase in pore fluid pressure is one of the important physical mechanisms triggering aftershock generation. We obtained evidence that pore fluid pressure increased around the southern part of the main rupture zone after the mainshock, examining temporal changes in types of focal mechanism data. The average increases in pore fluid pressure were estimated to be 17, 20, and 17 MPa at depths of 5, 10, and 15 km, respectively. These large increases in pore fluid pressure cannot be explained under the undrained condition. The spatial derivative of the pore fluid pressure field in the depth direction implies that fluid supply from greater depths may have controlled increases in seismicity rates that followed the large earthquake.

Monitoring of Gas Emissions in Light of an OEF Application

This study analyzes the possibility to use geophysical and geochemical parameters in an OEF (Operational Earthquake Forecasting) application correlated with short-term changes in seismicity rates using a magnitude–frequency relationship. Tectonic stress over the limits of rock elasticity generates earthquakes, but it is possible that the emission of gases increases as a result of the breaking process. The question is how reliable is the emission of radon-222 and Carbon Dioxide (CO2), with effects on air ionization and aerosol concentration, in an OEF application? The first step is to select the seismic area (in our study this is the Vrancea area characterized by deep earthquakes at the bend of the Carpathian Mountains), then determine the daily and seasonal evolution of the forecast parameters, their deviations from the normal level, the short-term changes in seismicity rates using a magnitude–frequency relationship and finally to correlate the data with recorded seismic events. The results of anomaly detection, effect evaluation and data analysis alert the beneficiaries specialized in emergency situations (Inspectorate for Emergency Situations, organizations involved in managing special events). Standard methods such as the standard deviation from the mean value, time gradient, cross correlation, and linear regression are customized for the geological specificity of the area under investigation. For detection we use the short-time-average through long-time-average trigger (STA/LTA) method on time-integral data and the daily–seasonal variation of parameters is correlated with atmospheric conditions to avoid false decisions. The probability and epistemic uncertainty of the gas emissions resulting from this study, in addition to other precursor factors such as air ionization, time between earthquakes, temperature in the borehole, telluric currents, and Gutenberg Richter “a-b” parameters, act as inputs into a logical decision tree, indicating the possibility of implementing an OEF application for the Vrancea area. This study is novel in its analysis of the Vrancea area and performs a seismic forecasting procedure in a new form compared to the known ones.

Seismicity and Stress Associated With a Fluid‐Driven Fracture: Estimating the Evolving Geometry

AbstractA coupled approach, combining the theory of rate‐ and state‐dependent friction and methods from poroelasticity, forms the basis for a quantitative relationship between displacements and fluid leak‐off from a growing fracture and changes in the rate of seismic events in the region surrounding the fracture. Poroelastic Green's functions link fracture aperture changes and fluid flow from the fracture to changes in the stress field and pore pressure in the adjacent formation. The theory of rate‐ and state‐dependent friction provides a connection between Coulomb stress changes and variations in the rate of seismic events. Numerical modeling indicates that the Coulomb stress changes can vary significantly between formations with differing properties. The relationship between the seismicity rate changes and the changes in the formation stresses and fluid pressure is nonlinear, but a transformation produces a quantity that is linearly related to the aperture changes and fluid leak‐off from the fracture. The methodology provides a means for mapping changes in seismicity into fracture aperture changes and to image an evolving fracture. An application to observed microseismicity associated with a hydrofracture reveals asymmetric fracture propagation within two main zones, with extended propagation in the upper zone. The time‐varying volume of the fracture agrees with the injected volume, given by the integration of rate changes at the injection well, providing validation of the estimated aperture changes.