Burst Of Seismicity Research Articles

Real-time assessment of potential seismic migration within a monitoring network using Red-flag SARA

Magma opening new fluid pathways through the crust can generate migrating seismic sources following the trail of the magma. By using Seismic Amplitude Ratio Analysis (SARA), it is possible to detect this seismic migration simply from the amplitudes of continuous data recorded at different stations in a network, without having to do any picking of seismic phases. In this study, we present a modified method – Red-flag SARA, which adapts SARA for real-time monitoring. Red-flag SARA provides a quantitative tool to analyse amplitude ratios between stations in a network and detect temporal changes in these ratios. Since such changes imply seismic source location variations, Red-flag SARA is a handy tool during seismic crises to quickly answer the question of whether seismic activity, and therefore magma, is migrating or not. We tested Red-flag SARA on synthetic data and validated it using real data from two volcanoes – Piton de la Fournaise, Reunion Island, and Gede, Indonesia, for three scenarios: 1) magma migration ending as intrusion, 2) migration leading to eruption and 3) a burst of seismicity with no magma migration.

Earthquakes Induced by Hydraulic Fracturing Are Pervasive in Oklahoma

AbstractWastewater disposal is generally accepted to be the primary cause of the increased seismicity rate in Oklahoma within the past decade, but no statewide analysis has investigated the contribution of hydraulic fracturing (HF) to the observed seismicity or the seismic hazard. Utilizing an enhanced seismicity catalog generated with multistation template matching from 2010 to 2016 and all available hydraulic fracturing information, we identified 274 HF wells that are spatiotemporally correlated with bursts of seismicity. The majority of HF‐induced seismicity cases occurred in the SCOOP/STACK plays, but we also identified prominent cases in the Arkoma Basin and some more complex potential cases along the edge of the Anadarko Platform. For HF treatments where we have access to injection parameters, modeling suggests that poroelastic stresses are likely responsible for seismicity, but we cannot rule out direct pore pressure effects as a contributing factor. In all of the 16 regions we identified, ≥75% of the seismicity correlated with reported HF wells. In some regions, >95% of seismicity correlated with HF wells and >50% of the HF wells correlated with seismicity. Overall, we found ~700 HF‐induced earthquakes with M ≥ 2.0, including 12 events with M 3.0–3.5. These findings suggest state regulations implemented in 2018 that require operators in the SCOOP/STACK plays to take action if a M > 2 earthquake could have a significant impact on future operations.

Mainshock‐Aftershock Clustering in Volcanic Regions

AbstractEarthquakes break their general Poissonean behavior through two types of seismic bursts: swarms and mainshock‐aftershock sequences. The former is commonly thought to dominate in volcanic and geothermal regions, but aftershock production, including within swarms, is not well studied in volcanic regions. Here we compare mainshock‐aftershock clustering in active volcanic regions in Japan to nearby nonvolcanic regions. We find that aftershock production is similar in both areas by two separate metrics: (1) Both volcanic and nonvolcanic regions have similar proportions of areas that cluster into mainshock‐aftershock sequences. (2) Volcanic areas with mainshock‐aftershock sequences have aftershock productivity at least as high as nonvolcanic regions. We also find that volcano‐tectonic events that are precursors to an eruption are more common at volcanoes without mainshock‐aftershock clusters than at volcanoes with well‐defined mainshock‐aftershock clusters. This last finding hints at a strategy to identify volcanic systems where cataloged earthquakes are good predictors of behavior.

The Tolud Burst of Seismicity and the Earthquake of November 30, 2012 (MC = 5.4, MW = 4.8) that Accompanied the Start of the 2012‒2013 Tolbachik Eruption

This paper reports a study of the Tolud earthquake sequence; the sequence was a burst of shallow seismicity between November 28 and December 7, 2012; it accompanied the initial phase in the Tolbachik Fissure Eruption of 2012‒2013. The largest earthquake (the Tolud earthquake of November 30, 2012, to be referred to as the Tolud Earthquake in what follows, with KS = 11.3, ML = 4.9, MC = 5.4, and MW = 4.8) is one of the five larger seismic events that have been recorded at depths shallower than 10 km beneath the entire Klyuchevskoi Volcanic Cluster in 1961‒2015. It was found that the Tolud earthquake sequence was the foreshock–aftershock process of the Tolud Earthquake. This is one of the larger seismicity episodes ever to have occurred in the volcanic areas of Kamchatka. Data of the Kamchatka seismic stations were used to compute some parameters for the Tolud Earthquake and its largest (ML = 4.3) aftershock; the parameters include the source parameters and mechanisms, and the moment magnitudes, since no information on these is available at the world seismological data centers. The focal mechanisms for the Tolud Earthquake and for its aftershock are consistent with seismic ruptures at a tension fault in the rift zone. Instrumental data were used to estimate the intensity of shaking due to the Tolud Earthquake. We discuss the sequence of events that was a signature of the time-dependent seismic and volcanic activity that took place in the Tolbachik zone in late November 2012 and terminated in the Tolud burst of seismicity. Based on the current ideas of the tectonics and magma sources for the Tolbachik volcanic zone, we discuss possible causes of these earthquakes.

Earthquake forecasting during the complex Amatrice-Norcia seismic sequence.

Earthquake forecasting is the ultimate challenge for seismologists, because it condenses the scientific knowledge about the earthquake occurrence process, and it is an essential component of any sound risk mitigation planning. It is commonly assumed that, in the short term, trustworthy earthquake forecasts are possible only for typical aftershock sequences, where the largest shock is followed by many smaller earthquakes that decay with time according to the Omori power law. We show that the current Italian operational earthquake forecasting system issued statistically reliable and skillful space-time-magnitude forecasts of the largest earthquakes during the complex 2016-2017 Amatrice-Norcia sequence, which is characterized by several bursts of seismicity and a significant deviation from the Omori law. This capability to deliver statistically reliable forecasts is an essential component of any program to assist public decision-makers and citizens in the challenging risk management of complex seismic sequences.

CHARACTERISTICS OF SEISMIC EXCITATIONS IN CORINTH GULF (GREECE)

Seismic excitations occur as mainshock-aftershock sequences (MS-AS) encompassing a strong event called mainshock with the largest magnitude in the set, or as earthquake swarms (ES) when a distinctive main event is absent. In regions as the gulf of Corinth, where active deformation is manifested with frequent seismicity bursts, it is important to distinguish MS-AS from ES for providing information on the physical process of earthquake generation and contribute to the seismic hazard assessment. For this purpose, a highly accurate local earthquake catalogue was compiled and an effort was made for clusters identification after establishing certain criteria based on spatio-temporal seismicity properties. The skewness and kurtosis of moment release history were calculated considering the normalized time of every event in a cluster since the starting time of the cluster and its seismic moment. For MS-AS we found large positive values for skewness and kurtosis contrary to ES that exhibit negative to low positive values for skewness and even lower values for kurtosis.In order to verify the classification of clusters, the b-value, the spatial size and the number of events of each cluster were examined. Finally, a scaling relation between the length of the rupture zone and magnitude derived for the MS-AS sequences.

A Review of Rock Bolt Monitoring Using Smart Sensors.

Rock bolts have been widely used as rock reinforcing members in underground coal mine roadways and tunnels. Failures of rock bolts occur as a result of overloading, corrosion, seismic burst and bad grouting, leading to catastrophic economic and personnel losses. Monitoring the health condition of the rock bolts plays an important role in ensuring the safe operation of underground mines. This work presents a brief introduction on the types of rock bolts followed by a comprehensive review of rock bolt monitoring using smart sensors. Smart sensors that are used to assess rock bolt integrity are reviewed to provide a firm perception of the application of smart sensors for enhanced performance and reliability of rock bolts. The most widely used smart sensors for rock bolt monitoring are the piezoelectric sensors and the fiber optic sensors. The methodologies and principles of these smart sensors are reviewed from the point of view of rock bolt integrity monitoring. The applications of smart sensors in monitoring the critical status of rock bolts, such as the axial force, corrosion occurrence, grout quality and resin delamination, are highlighted. In addition, several prototypes or commercially available smart rock bolt devices are also introduced.

A nonplanar slow rupture episode during the 2000 Miyakejima dike intrusion

AbstractMagmatic intrusions release extensional strain in the Earth's crust upon availability of magma. Intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes. The 2000 Miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far, with five Ml>6 earthquakes. We analyze the seismicity and deformation induced by the Miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode. In six earthquake bursts lasting few hours and migrating at ∼1 km h−1 we find candidates for slow earthquakes. Each burst nucleated at the tips of previous bursts, suggesting stress interaction. The variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures, consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time, such as those induced by a dike. Based on dislocation models, we find that deformation is best explained by aseismic slip (in addition to the seismic burst), with a moment 1.3 to 2.3 times larger than the earthquakes' seismic moment, and opening of 0.20 ± 0.07 m on the dike. The aseismic slip occurred over a few hours, with moment, duration, and migration velocity consistent with that of previously observed slow slip events. We argue that the seismic bursts are likely driven by slow slip, sharing most properties with tectonic slow slip events and swarms, but occurring on a set of nonaligned faults.

2013 Seismic swarm recorded in Galati area, Romania: focal mechanism solutions

An unusual seismic swarm started on September 23, 2013, close to Galati city, in Izvoarele region (Romania), and lasted until November 12, 2013. 406 earthquakes were recorded during several phases of seismic activity. The strongest events—a magnitude 3.9 earthquake, occurred on September 29, and two ML 3.8 shocks, occurred on October 3 and 4, respectively, were accompanied by specific seismicity bursts. The seismogenic region of the swarm is situated between two main crustal faults, which builds up the primary fault system, oriented SE–NW: New Trotus Fault (at the limit between North Dobrogea and Scythian Platform) to the North and east, and Peceneaga Camena fault (which separates North Dobrogea block from the Moesian Platform) to the South. The epicentral zone belongs to a complex tectonic area, in which a secondary fault system—lying NE–SW, perpendicular to the primary system—is also present. The focal mechanisms show normal faulting, with an important strike-slip component, one of the nodal planes being oriented roughly in a NE–SW direction. The objective of this study is to investigate the seismic swarm recorded in a new seismic area of Romania, near the town Galati in Izvoarele region. We show detailed hypocentral location, focal mechanisms and the correlation between seismicity and tectonic structures.

Frictional strength and heat flow of southern San Andreas Fault

Frictional strength and heat flow of faults are two related subjects in geophysics and seismology. To date, the investigation on regional frictional strength and heat flow still stays at the stage of qualitative estimation. This paper is concentrated on the regional frictional strength and heat flow of the southern San Andreas Fault (SAF). Based on the in situ borehole measured stress data, using the method of 3D dynamic faulting analysis, we quantitatively determine the regional normal stress, shear stress, and friction coefficient at various seismogenic depths. These new data indicate that the southern SAF is a weak fault within the depth of 15 km. As depth increases, all the regional normal and shear stresses and friction coefficient increase. The former two increase faster than the latter. Regional shear stress increment per kilometer equals 5.75 ± 0.05 MPa/km for depth ≤15 km; regional normal stress increment per kilometer is equal to 25.3 ± 0.1 MPa/km for depth ≤15 km. As depth increases, regional friction coefficient increment per kilometer decreases rapidly from 0.08 to 0.01/km at depths less than ~3 km. As depth increases from ~3 to ~5 km, it is 0.01/km and then from ~5 to 15 km, and it is 0.002/km. Previously, frictional strength could be qualitatively determined by heat flow measurements. It is difficult to obtain the quantitative heat flow data for the SAF because the measured heat flow data exhibit large scatter. However, our quantitative results of frictional strength can be employed to investigate the heat flow in the southern SAF. We use a physical quantity P f to describe heat flow. It represents the dissipative friction heat power per unit area generated by the relative motion of two tectonic plates accommodated by off-fault deformation. P f is called “fault friction heat.” On the basis of our determined frictional strength data, utilizing the method of 3D dynamic faulting analysis, we quantitatively determine the regional long-term fault friction heat at various seismogenic depths in the southern SAF. The new data show that as depth increases, regional friction stress increases within the depth of 15 km; its increment per kilometer equals 5.75 ± 0.05 MPa/km. As depth increases, regional long-term fault friction heat increases; its increment per kilometer is equal to 3.68 ± 0.03 mW/m2/km. The values of regional long-term fault friction heat provided by this study are always lower than those from heat flow measurements. The difference between them and the scatter existing in the measured heat flow data are mainly caused by the following processes: (i) heat convection, (ii) heat advection, (iii) stress accumulation, (iv) seismic bursts between short-term lull periods in a long-term period, and (v) influence of seismicity in short-term periods upon long-term slip rate and heat flow. Fault friction heat is a fundamental parameter in research on heat flow.

Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke

The role of static versus dynamic stresses in earthquake clusters is unclear. Analysis of earthquakes triggered by a dyke intrusion at an Icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering. Large earthquakes can generate small changes in static stress: increases that trigger aftershock swarms, or reductions that create a region of reduced seismicity—a stress shadow1,2. However, seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3,4. This makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks. Dyke intrusions do not generate dynamic stresses, so provide an unambiguous test of the stress shadow hypothesis. Here we use GPS and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath Barðarbunga Volcano, central Iceland, in August 2014. We find that during dyke emplacement, bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano. We calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke. Our results imply that static stress changes help control earthquake clustering. Similar small static stress changes may be important for triggering seismicity near geothermal areas, regions being hydrofractured and deflating oil and gas fields.

Geochemical evidence of different sources of long-period seismic events at Deception volcano, South Shetland Islands, Antarctica

AbstractThis is the first detailed analysis of a CO2diffuse degassing time series from Deception volcano, South Shetland Islands, Antarctica, performed during an episode of anomalously high long-period (LP) seismicity. Diffuse CO2emissions measured by an automatic geochemical station between 7 December 2009 and 13 February 2010 showed an excellent temporal agreement with the LP seismicity in December 2009. The absence of such a temporal correlation with the second burst of seismicity that occurred in late January 2010 suggests a different source for this LP activity. This was confirmed by analysis of seismic array data. The LP seismicity observed during December 2009 was caused by fluid-driven cracks that originated from pressure fluctuations in the volcano-hydrothermal systems beneath Deception volcano that were probably caused by a deep injection of undegassed magma before December 2009. The diffuse CO2degassing data have provided evidence of the activation of at least two different sources of seismicity during the study period at Deception volcano.

Investigating the final seismic swarm before the Iquique‐Pisagua 2014 Mw 8.1 by comparison of continuous GPS and seismic foreshock data

AbstractPreexisting networks of seismometers and continuous GPS in Northern Chile successfully captured surface motions and seismicity leading up to the 1 April Mw 8.1. Here we compare continuous GPS (cGPS) with predictions of seismic dislocations for the final foreshock swarm, beginning with the 16 March Mw 6.7. Results show that the cumulative cGPS motion can be largely explained by seismic slip because evolutions of cGPS positions for most stations stay within the ranges of seismic predictions (given sensible ranges of assumed source errors). However, cGPS motions between 18–21 and 25–31 March outpace seismic predictions, supporting the existence of aseismic transients that were most probably the afterslip from preceding bursts of seismicity. A parameter search reveals that the 16 March Mw 6.7 cGPS displacements can be recreated with a fault plane significantly rotated anticlockwise from the strike of the plate interface, suggesting that failure was on a structure other than the plate interface.

A detailed seismic anisotropy study during the 2011–2012 unrest period in the Santorini Volcanic Complex

The Santorini Volcanic Complex (SVC) is an area in the Southern Aegean (Greece) which has been characterized by low seismicity rates for the last decades, especially in the Santorini Caldera where they have been very low until 2010. This pattern changed completely in February 2011, when intense microseismic activity was initiated within the Caldera. During the manual analysis of the events, the shear-wave splitting phenomenon was observed, revealing the existence of an anisotropic upper crust in the SVC area. A detailed anisotropy study has been conducted using 231 events within the shear-wave window that fulfilled the selection criteria. The polarization direction of the fast shear-wave, the time-delay between the two split shear-waves and the source polarization direction were calculated after visual inspection, using both the polarigram and the hodogram representations. This procedure, applied for eight local stations, resulted in the determination of 340 splitting parameters. The obtained mean anisotropy directions are not homogeneous, revealing a complex regime in the activated area. Nevertheless, these results are explained by the APE model, related to the stress-sensitive behavior of fluid-saturated microcracked rocks. A detailed analysis of the temporal evolution of both the time-delay and anisotropy direction was carried out. The time-delays measured in the “band-1” window exhibit gradual increase and sudden drop that can be related to imminent bursts of seismicity, as well as to the major Mw=5.1 and 5.2 events which took place about 40km SW of Santorini on 26 and 27 January 2012, respectively. On the other hand, no significant temporal variations or 90° flips of the Sfast polarization direction were observed.

The Coulomb Stress Changes and Seismicity Rate due to the 1990 Mw 7.3 Rudbar Earthquake

We investigate correlation between the Coulomb stress changes and the spatial distribution of the aftershocks of the 1990 M w 7.3 Rudbar earthquake that occurred on and off the Rudbar fault. The Coulomb stress changes indicate that the Rudbar mainshock encouraged parts of the Kelishom and Kashachal strike‐slip faults (located east of the main rupture), as well as parts of the Manjil Thrust fault (located south of the main rupture). The central part of the Manjil Thrust, which is sandwiched between two stress shadow zones, experienced an increase in Coulomb stress. We observe that the events before and after the Rudbar mainshock have different spatial distribution patterns. We find that most of the aftershocks occurred in an area between the Kabateh and Zardgeli segments where the static Coulomb stress is high, while few aftershocks occurred in the stress shadow zone that extends to the northwest and southeast of the Rudbar rupture. The aftershocks that occurred in the stress shadow zones northwest of the Baklor segment were related to the continuation of the background seismicity after the mainshock. A burst of seismicity following the Rudbar earthquake south of the Zardgeli segment provides evidence for dynamic stress triggering for the aftershocks that affected these regions for the first 1–3 months after the mainshock. We also compare the Coulomb stress changes with the seismicity rate and find that the regions with high seismicity rate are in good agreement with the high stress such as the western end of the Baklor and an area between the Kabateh and Zardgeli segments. To validate the effects of the Coulomb stress on the seismicity rate, we resolved stress changes on the aftershock nodal planes and recognize that the aftershocks located between the Kabateh and Zardgeli segments and the surrounding areas were brought closer to failure.

The degassing character of a young volcanic center: Cerro Negro, Nicaragua

Cerro Negro volcano is a young basaltic cinder cone which is part of the Nicaraguan volcanic arc. Eruptive activity at Cerro Negro is characterized by explosive strombolian to subplinian eruptions driven by volatile-rich basaltic magma ascending rapidly from various crustal depths (>15 to 6 km) resulting in the onset of precursory activity only ∼30 min before an eruption. In this paper, we present a comprehensive degassing characterization of the volcano over a 4-year period aimed at improving our understanding of the magmatic plumbing network and its relationship with regional tectonics. A total of 124 individual soil gas samples were collected between 2010 and 2013 and analyzed for stable carbon isotopes (δ13C) from CO2. High temperature fumaroles were sampled for δ18O, δD, and 3He/4He isotope analysis, and major degassing zones were mapped using soil CO2 flux measurements. Gases at Cerro Negro are characterized by a strong 3He/4He mantle signature (6.3 to 7.3 RA), magmatic δ13C ratios (−2.3 to −3.0 ‰), meteoric δ18O and δD ratios, and stable CO2 fluxes (31 t d−1). The lack of δ13C fractionation and an increase in the relative mantle component from 2002 to 2012 suggest that the volatile flux at Cerro Negro originates from the mantle and ascends to the surface via a series of crustal fractures that act as permeable conduits. Despite the lack of new eruptions, the hydrothermal system of Cerro Negro continues to evolve due to seasonal inputs of meteoric water, slope failures that expose and bury sites of active degassing, and bursts of regional seismicity that have the potential to open up new conduits for gas release as well as magma. Continuing geophysical and geochemical monitoring of the main edifice and the recently formed south zone is essential, as the volcano remains overdue to erupt.

Step-like migration of early aftershocks following the 2007 Mw 6.7 Noto-Hanto earthquake, Japan

Seismic data reveal that the aftershock zone expands with time after a main shock event. Here we examine the aftershock sequence recorded during the first 32 days following the 2007 Noto-Hanto earthquake, Japan. By applying a matched-filter technique to the data, we detected about 10 times more events than those listed in the routinely constructed earthquake catalog. The aftershock area expanded along the fault strike as a logarithmic function of time, beginning immediately after the main shock. Aftershock expansion toward the SW was especially extensive and developed more rapidly than toward the NE. Interestingly, the aftershock area expanded in a step-like manner by the activation of a series of spatially clustered seismic bursts. Spatial correlation between the aftershock extension and the afterslip distribution suggests that the expansion of the aftershock area could be mainly driven by aseismic afterslip. The aftershock area continues to expand, even though 7 years have now passed since the main shock.

Possible evidence of remotely triggered and delayed seismicity due to the 2001 Bhuj earthquake (Mw = 7.6) in western India

Remote triggering by large earthquakes at regional distances is a globally observed phenomenon. However, there are no reports of observations of dynamic triggering at regional distances of several source lengths associated with the large Mw = 7.6 Bhuj earthquake of January 26, 2001, in western India. In the present study, a swarm of over 140 microearthquakes that occurred about 500 km southeast of Bhuj, in the geothermal province of the Western Ghats in the Deccan volcanic province (DVP) of India, immediately after the occurrence of the Bhuj earthquake in 2001 is investigated. The post-Bhuj seismicity (M < 2.0) occurred in three bursts spread over 2 months with each burst of intense activity lasting for 2–3 days. All the three bursts of seismicity occurred in the same volume along a 5-km-long NW–SE trending fault. The temporal coincidence and the sudden rise in seismicity that interrupts the characteristically low background seismicity strongly suggest that the Bhuj earthquake may have remotely triggered this activity. The triggered seismicity began approximately 2.5 h after the onset of the Bhuj mainshock and continued well after the passage of the surface waves, suggesting that the dynamic stresses possibly gave rise to secondary time-dependent mechanisms leading to the triggering. It is proposed that the triggered and delayed seismicity is possibly a consequence of the redistribution in pore fluid pressure due to the Bhuj earthquake. This is the first documented observation of remotely triggered seismicity at regional distances due to the Bhuj earthquake.

Spatial migration of earthquakes within seismic clusters in Southern California: Evidence for fluid diffusion

Seismicity within many earthquake swarms is observed to migrate slowly with time, which may reflect event triggering due to slow fault slip or fluid flow. We search for this behavior in Southern California by applying a weighted least squares method to quantify event migration within 69 previously observed seismicity bursts. We obtain best‐fitting migration directions and velocities, and compute a statistical migration significancesm for each burst using a bootstrap resampling method. We define 37 bursts with sm ≥ 0.8 as the migration group, and 32 bursts with sm &lt; 0.8 as the non‐migration group. To explore differences between the two groups, for each burst we compute effective stress drop (Δσquasi, the ratio between total moment and radius), the skew of the moment release time series (μ), the timing of the largest event (tmax), and the distance separation between the first half and second half of the sequence (ds). As expected, the migration group features larger ds and lower Δσquasi, consistent with higher migration significance. It also features lower μ and higher tmax, similar to observations from swarms in the Salton Trough, while the non‐migration group is more similar to main shock‐aftershock sequences. To explore possible fluid involvement, we model the migration behavior with the fluid diffusion equation, and identify 18 bursts with diffusion coefficients ranging from 0.01 to 0.8 m2/s, with the majority below 0.16 m2/s. The obtained diffusion coefficients and migration behavior are similar to the Reservoir‐induced seismicity beneath the Açu reservoir in Brazil. The majority of normal faulting events are associated with these 18 bursts, while the non‐migration group has the most reverse faulting events, indicating a possible link between sequence type and focal mechanism.

Relationship between the rock mass deformation and places of occurrence of seismological events

Static effort of rock mass very rarely causes of rock burst in polish coal mines. Rock bursts with source in the seismic tremor within the roof rock layers are prevailing. A seismic tremor is an effect of rupture or sliding in roof layers above the exploited panel in coal seam, sometime in a distance from actual exploitation. Sliding, as a rule occurs in fault zone and tremors in it are expected, but monolithic layer rupture is very hard to predict. In a past few years a practice of analyzing state of deformation in high energy seismic tremors zones has been employed. It let gathering experience thanks to witch determination of dangerous shape of reformatted roof is possible. In the paper some typical forms of roof rocks deformations leading to seismic tremor occurrence will be presented. In general these are various types of multidirectional rock layers bending. Real examples of seismic events and rock bursts will be shown.