Earthquake Report: Greece/Albania

We are currently having a swarm of earthquakes along the political boundary which forms Greece and Albania. These earthquakes are just north of the western terminus of the North Anatolia fault (where it ends in Greece). To the north of the NAF, in Greece, is a thrust belt that extends northwards along the Ionian Sea. This thrust belt appears to be related to Cenozoic extension in the southern Balkans (Burchfiel et al., 2008). There was an M 6.5 earthquake to the southwest of this swarm on 2015.11.17.
In the map below I plot the epicenters of earthquakes from the past 30 days of magnitude greater than M = 2.5. The epicenters have colors representing depth in km. The USGS plate boundaries are plotted vs color.
Today’s swarm appears to have a northwesterly strike. The moment tensor suggests either a northeastern dip or a southwestern dip with a slightly oblique motion. Based on the regional tectonics, i interpret this to have a northwest strike, northeastern dip, with a right-lateral oblique slip (Picha, 2002; Kokkalas et al., 2006).
I also plot the “Did You Feel It?” reports of ground shaking. The color of the dots uses the Modified Mercalli Intensity (MMI) scale. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. There is a color legend for these reports in the upper left corner.

    Here are the USGS earthquake pages for the larger magnitude earthquakes.

  • 2016.10.15 20:14:49 M 5.3
  • 2016.10.16 00:09:59 M 4.9
  • 2016.10.16 00:41:16 M 5.0
  • 2016.10.16 00:48:16 M 4.9
  • 2016.10.16 00:02:21 M 5.0
  • 2016.10.16 00:03:40 M 5.1

I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.

    I include some inset figures.

  • In the lower left corner is a figure that shows the general tectonics of the Mediterranean Sea region. The tectonics here are dominated by the compressional tectonics related to the Alpide Belt, a convergent plate boundary formed in the Cenozoic that extends from Australia to Morocco.
  • In the upper left corner is a larger scale map showing how the NAF extends into Greece (with multiple splays) and terminates at the western end of the Helenic Arc. At this intersection is the southern end of a thrust belt (Kokkalas et al., 2006). I placed a red circle in the approximate location of today’s swarm.
  • In the lower right corner is another tectonic map that shows the region of compression in the eastern Ionian Sea.
  • In the upper right corner is a cross section (A-A’) that is located on the map with a white line with dots at each end (A-A’). In Dilek (2006) there are numerous cross sections that show similar structures.


  • For more on the graphical representation of moment tensors and focal mechanisms, check this IRIS video out.
    Here is the earthquake report poster from the strike-slip earthquakes in November 2015 along the Kefalonia fault zone.

      Here are the USGS web pages for these 3 earthquakes:

    • 2015.11.17 M 6.5
    • 2015.11.17 M 5.4
    • 2015.11.18 M 4.7


  • Here is another map of the region showing the compression in this region (Burchfiel et al., 2008 ). I include the figure caption below in blockquote.

  • Location of the South Balkan extensional system (SBER) withing the eastern European region. The system today is within the southern Balkan region north of the North Anatolian fault (NAF), shown by the horizontal line patter. Retreating subduction zones and related backarc extensional areas for the Mediterranean region are shown in blue , and advancing subduction zones an related are a of backarc shortening are shown in red). Backarc extensional regions are shown by dotted parttern. KF = Kefalonia fault zone.

  • The following three figures are from Dilek et al., 2006. The locations of the cross sections are shown on the map as orange lines.
  • Here is the map (Dilek et al., 2006). I include the figure caption below in blockquote.

  • Simplified tectonic map of the Mediterranean region showing the plate boundaries, collisional zones, and directions of extension and tectonic transport. Red lines A through G show the approximate profile lines for the geological traverses depicted in Figure 2. MHSZ—mid-Hungarian shear zone; MP—Moesian platform; RM—Rhodope massif; IAESZ— Izmir-Ankara-Erzincan suture zone; IPS—Intra-Pontide suture zone; ITS—inner Tauride suture zone; NAFZ—north Anatolian fault zone; KB—Kirsehir block; EKP—Erzurum-Kars plateau; TIP—Turkish-Iranian plateau.

  • Here are cross sections A-D (Dilek et al., 2006). I include the figure caption below in blockquote.



  • Simplified tectonic cross-sections across various segments of the broader Alpine orogenic belt.

  • (A) Eastern Alps. The collision of Adria with Europe produced a bidivergent crustal architecture with both NNW- and SSE-directed nappe structures that involved Tertiary molasse deposits, with deep-seated thrust faults that exhumed lower crustal rocks. The Austro-Alpine units north of the Peri-Adriatic lineament represent the allochthonous outliers of the Adriatic upper crust tectonically resting on the underplating European crust. The Penninic ophiolites mark the remnants of the Mesozoic ocean basin (Meliata). The Oligocene granitoids between the Tauern window and the Peri-Adriatic lineament represent the postcollisional intrusions in the eastern Alps. Modified from Castellarin et al. (2006), with additional data from Coward and Dietrich (1989); Lüschen et al. (2006); Ortner et al. (2006).
  • (B) Northern Apennines. Following the collision of Adria with the Apenninic platform and Europe in the late Miocene, the westward subduction of the Adriatic lithosphere and the slab roll-back (eastward) produced a broad extensional regime in the west (Apenninic back-arc extension) affecting the Alpine orogenic crust, and also a frontal thrust belt to the east. Lithospheric-scale extension in this broad back-arc environment above the west-dipping Adria lithosphere resulted in the development of a large boudinage structure in the European (Alpine) lithosphere. Modified from Doglioni et al. (1999), with data from Spakman and Wortel (2004); Zeck (1999).
  • (C) Western Mediterranean–Southern Apennines–Calabria. The westward subduction of the Ionian seafloor as part of Adria since ca. 23 Ma and the associated slab roll-back have induced eastward-progressing extension and lithospheric necking through time, producing a series of basins. Rifting of Sardinia from continental Europe developed the Gulf of Lion passive margin and the Algero-Provencal basin (ca. 15–10 Ma), then the Vavilov and Marsili sub-basins in the broader Tyrrhenian basin to the east (ca. 5 Ma to present). Eastward-migrating lithospheric-scale extension and
    necking and asthenospheric upwelling have produced locally well-developed alkaline volcanism (e.g., Sardinia). Slab tear or detachment in the Calabria segment of Adria, as imaged through seismic tomography (Spakman and Wortel, 2004), is probably responsible for asthenospheric upwelling and alkaline volcanism in southern Calabria and eastern Sicily (e.g., Mount Etna). Modified from Séranne (1999), with additional data from Spakman et al. (1993); Doglioni et al. (1999); Spakman and Wortel (2004); Lentini et al. (this volume).
  • (D) Southern Apennines–Albanides–Hellenides. Note the break where the Adriatic Sea is located between the western and eastern sections along this traverse. The Adria plate and the remnant Ionian oceanic lithosphere underlie the Apenninic-Maghrebian orogenic belt. The Alpine-Tethyan and Apulian platform units are telescoped along ENE-vergent thrust faults. The Tyrrhenian Sea opened up in the latest Miocene as a back-arc basin behind the Apenninic-Maghrebian mountain belt. The Aeolian volcanoes in the Tyrrhenian Sea represent the volcanic arc system in this subduction-collision zone environment. Modified from Lentini et al. (this volume). The eastern section of this traverse across the Albanides-Hellenides in the northern Balkan Peninsula shows a bidivergent crustal architecture, with the Jurassic Tethyan ophiolites (Mirdita ophiolites in Albania and Western Hellenic ophiolites in Greece) forming the highest tectonic nappe, resting on the Cretaceous and younger flysch deposits of the Adria affinity to the west and the Pelagonia affinity to the east. Following the emplacement of the Mirdita- Hellenic ophiolites onto the Pelagonian ribbon continent in the Early Cretaceous, the Adria plate collided with Pelagonia-Europe obliquely starting around ca. 55 Ma. WSW-directed thrusting, developed as a result of this oblique collision, has been migrating westward into the peri-Adriatic depression. Modified from Dilek et al. (2005).
  • (E) Dinarides–Pannonian basin–Carpathians. The Carpathians developed as a result of the diachronous collision of the Alcapa and Tsia lithospheric blocks, respectively, with the southern edge of the East European platform during the early to middle Miocene (Nemcok et al., 1998; Seghedi et al., 2004). The Pannonian basin evolved as a back-arc basin above the eastward retreating European platform slab (Royden, 1988). Lithospheric-scale necking and boudinage development occurred synchronously with this extension and resulted in the isolation of continental fragments (e.g., the Apuseni mountains) within a broadly extensional Pannonian basin separating the Great Hungarian Plain and the Transylvanian subbasin. Steepening and tearing of the west-dipping slab may have caused asthenospheric flow and upwelling, decompressional melting, and alkaline volcanism (with an ocean island basalt–like mantle source) in the Eastern Carpathians. Modified from Royden (1988), with additional data from Linzer (1996); Nemcok et al. (1998); Doglioni et al. (1999); Seghedi et al. (2004).
  • (F) Arabia-Eurasia collision zone and the Turkish-Iranian plateau. The collision of Arabia with Eurasia around 13 Ma resulted in (1) development of a thick orogenic crust via intracontinental convergence and shortening and a high plateau and (2) westward escape of a lithospheric block (the Anatolian microplate) away from the collision front. The Arabia plate and the Bitlis-Pütürge ribbon continent were probably amalgamated earlier (ca. the Eocene) via a separate collision event within the Neo-Tethyan realm. BSZ—Bitlis suture zone; EKP—Erzurum-Kars plateau. A slab break-off and the subsequent removal of the lithospheric mantle (lithospheric delamination) beneath the eastern Anatolian accretionary complex caused asthenospheric upwelling and extensive melting, leading to continental volcanism and regional uplift, which has contributed to the high mean elevation of the Turkish-Iranian plateau. The Eastern Turkey Seismic Experiment results have shown that the crustal thickness here is ~ 45–48 km and that the Turkish-Iranian plateau is devoid of mantle lithosphere. The collision-induced convergence has been accommodated by active diffuse north-south shortening and oblique-slip faults dispersing crustal blocks both to the west and the east. The late Miocene through Plio-Quaternary volcanism appears to have become more alkaline toward the south in time. The Pleistocene Karacadag shield volcano in the Arabian foreland represents a local fissure eruption associated with intraplate extension. Data from Pearce et al. (1990); Keskin (2003); Sandvol et al. (2003); S¸engör et al. (2003).
  • (G) Africa-Eurasia collision zone and the Aegean extensional province. The African lithosphere is subducting beneath Eurasia at the Hellenic trench. The Mediterranean Ridge represents a lithospheric block between the Africa and Eurasian plate (Hsü, 1995). The Aegean extensional province straddles the Anatolide-Tauride and Sakarya continental blocks, which collided in the Eocene. NAF—North Anatolian fault. South-transported Tethyan ophiolite nappes were derived from the suture zone between these two continental blocks. Postcollisional granitic intrusions (Eocone and Oligo-Miocene, shown in red) occur mainly north of the suture zone and at the southern edge of the Sakarya continent. Postcollisional volcanism during the Eocene–Quaternary appears to have migrated southward and to have changed from calc-alkaline to alkaline in composition through time. Lithospheric-scale necking, reminiscent of the Europe-Apennine-Adria collision system, and associated extension are also important processes beneath the Aegean and have resulted in the exhumation of core complexes, widespread upper crustal attenuation, and alkaline and mid-ocean ridge basalt volcanism. Slab steepening and slab roll-back appear to have been at work resulting in subduction zone magmatism along the Hellenic arc.

Earthquake Report: Italy

There was a M 6.2 earthquake in Italy tonight. Here is the USGS website for today’s earthquake. There is lots of information about the tectonics of this region. I can hardly do justice to all the people who have worked here. It seems like every route I take for more information, I get 10 more publications.
This earthquake is north of the region that had an M 6.3 earthquake in 2009 that led to an interesting (putting it nicely) interaction between scientists, public employees/politicians, and the legal system. Basically, several seismologists were sentenced to prison. More on this is found online, for example, here and here.
Below is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The tectonics of this region has many normal (extensional) faults, which explain the extensional moment tensor. However, I do not know enough of this region to interpret is this is an east or west dipping fault that ruptured (depends upon which side of which basin experience this earthquake; see below).

    I include some inset figures and maps.

  • In the upper right corner I include the Rapid Assessment of an Earthquake’s Impact (PAGER) report. More on the PAGER program can be found here. An explanation of a PAGER report can be found here. PAGER reports are modeled estimates of damage. On the top is a histogram showing estimated casualties and on the right is an estimate of possible economic losses. This PAGER report suggests that there will be quite a bit of damage from this earthquake (and casualties).
  • Below that I show the USGS plot of “Did You Feel It?” reports compared to the estimates of ground shaking from Ground Motion Prediction Equation (GMPE) estimates. The relations between ground shaking and distance to an earthquake are also known as attenuation relations as the ground motions diminish (get attenuated) with distance from the earthquake.
  • To the left of the PAGER report I include a basic tectonic map of this region. Maps with local (larger) scale have much more detailed views of the faulting.
  • In the lower left corner is a map showing a series of earthquake swarms that occurred between 1916 and 1920, rupturing across the Apennines in northern Italy. This is just to the north of tonight’s M 6.2 earthquake. It is interesting as Baize posted on twitter some accounts of this earthquake series on twitter yesterday. There is another map showing greater detail of the 1916 swarm.



I also plot a moment tensor from an earthquake in the western Mediterranean from 2016.01.24 in the above map. Here is my Earthquake Report for that seismicity and below is the map from that report.


In late 2015 (2015.11.17) there was a M 6.5 earthquake along a fault related to the terminus of the North Anatolian fault system in western Greece. Here is my earthquake report for that seismicity and below is my map from that report. Below this first map is another map that shows some aftershocks.


Here is an updated map that shows a couple more aftershocks, at a large (local) scale. I have included the moment tensors for the two largest aftershocks.


For more on the graphical representation of moment tensors and focal mechanisms, check this IRIS video out:

    Here are some observations made by others.

  • Susan Hough (USGS) asked people tonight what they thought about explaining why the “DYFI” reports seemed too small compared to the GMPE model predictions. So far, I am unsatisfied with the answers. Looking at the plot from the 2009 M 6.3 earthquake, the region’s low population density would not appear to explain this discrepancy. Perhaps it is because today’s earthquake happened at night time, so maybe people have not yet reported yet. Below I include these GMPE/DYFI plots for both 2016.08.24 M 6.2 and 2009.04.06 M 6.3 earthquakes. Interesting that the DYFI reports for the 2009 earthquake also have higher MMI values, in general, than the 2016 earthquake. The difference between a M 6.2 and > 6.3 earthquake is about 3 times (a M 6.3 releases about 3 times as much energy as a M 6.2 earthquake), but these maps seem much more different than that. I plot the DYFI maps below the attenuation plots.
  • 2016.08.24

  • 2009.04.06

  • 2016.08.24

  • 2009.04.06

  • David Schwartz (USGS) noted that tonight’s earthquake is “between the 1997 Assisi aftershock zone and the north end of the 2009 l’aquila rupture” and may be a “foreshock to a 1915-like Fucino rupture.” So we need to look at these two earthquakes to learn more about what Schwartz is talking about. Here is a web post about an INQUA workshop held in “Pescina, to commemorate the centenary of the 13/1/1915 M7 Fucino Earthquake.” This was posted by Stephanie Baize who is also on twitter. Follow him to learn more about tonight’s earthquake. There is a great paper that discusses the 1915 earthquake sequence that Schwartz was talking about here (Galadini and Galli, 1999). A more recent paper also discusses the faulting in this region (Palumbo et al., 2004).
    Here are some other maps that might help. (well, one so far)

  • This Billi et al. (2006) map shows some of these west dipping normal faults in central Italy, just south of the Apennines.

  • There are some excellent maps and figures from a study from 2004 (Boncio et al, 2004). This material was posted on twitter here.

Earthquake Report: Mediterranean!

We just had a M 6.1 earthquake and a few aftershocks (M 4-5) in the western Mediterranean,
Here is the USGS website for this earthquake.
Here is a map showing the 5 largest earthquakes as circles.
There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.


For more on the graphical representation of moment tensors and focal mechnisms, check this IRIS video out:

Based on the mapping presented by Gracia et al (2012), Casciello et al. (2016), and the bathymetry, this earthquake may have ruptured one of the northeast striking structures that are shown in the lower left part of the Gracia et al. (2012) map. Therefore I interpret this earthquake to be a left-lateral strike-slip earthquake.
Here is a close up of Gracia et al. (2012) Figure 1. I provide their caption below in blockquote.

Figure 1. Schematic geological map of the Westernmost Mediterranean highlighting the position of the Alboran Domain enclosed between Iberia and northwest Africa. Its metamorphic rocks compose the floor of the western Alboran Sea and form the inner zones of the Betics and Rif mountain chains.

Here is the Casciello et al (2016) figure showing their tectonic interpretation. Figure is their map and Figure 2 is an earlier tectonic interpretation (Andrieux et al., 1971). I provide their caption below in blockquote.

Fig. 1. Regional topographic and bathymetric map of the southeast Iberian margin constructed from digital grids released by SRTM-3, IEO bathymetry (Ballesteros et al., 2008; Mu˜noz et al., 2008) and MEDIMAP multibeam compilation (MediMap et al., 2008) at  90m grid-size. Epicenters of the largest historical earthquakes (MSK Intensity>VIII) in the region are depicted by a white star (I.G.N., 2010). Grey arrows pointing opposite each other show the direction of convergence between the Eurasian and African plates from NUVEL1 model (DeMets et al., 2010). The black outlined rectangle depicts the study area presented in Fig. 2. BSF: Bajo Segura Fault; AMF: Alhama de Murcia Fault, PF: Palomares Fault, CF: Carboneras Fault, YF: Yusuf Fault, AR: Alboran Ridge. Inset: Plate tectonic setting and main geodynamic domains of the south Iberian margin along the boundary between the Eurasian and African Plates.

Fig. 3. Original model by Andrieux et al. (1971) to explain the formation of the Gibraltar Arc. The Alboran microplate would resist the eastward movement of the European and African plates, which are
forced by oceanic expansion in the Atlantic, causing the formation of the Betic-Rif chains.

Earthquake Report: Greece!

Late last night (my time) there was an earthquake in Greece with a USGS magnitude of M = 6.5. Here is the USGS web site for this earthquake. Greece is at the intersection of a complex configuration of plate boundaries. To the south is a subduction zone that is part of the plate boundary formed between the Africa/India-Australia plate to the south and the Eurasia plate to the north. This plate boundary extends from northeast of Australia to west of Portugal and is responsible for the uplift of the tallest mountains of the world in the Himalayas and the Alps. One of the most active and devastating strike slip faults, the North Anatolian fault (NAF), strikes from the north end of Turkey, through the Aegean Sea, and bifurcates (more than 2 splays) through Greece. Today’s earthquake appears to have ruptured a fault related to the Kefalonia fault (KF), the only strand extension of the NAF that makes it completely through Greece.
Here is a map that shows the earthquake epicenter as a gold star, with ground shaking contours that use the Modified Mercalli Intensity Scale. I include maps that others have produced that help us interpret the regional tectonics. See references below.
I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
Based on the tectonic maps from Vött (2007) and Burchfiel et al. (2008), and the moment tensor, I interpret this earthquake to be related to the Kefalonia fault (KF) system and is a right lateral strike-slip earthquake. I also include, as an inset, the GPS velocity field map from Hamilton (2007; see below).


Here is an updated map that shows a couple more aftershocks, at a large (local) scale. I have included the moment tensors for the two largest aftershocks.

    Here are the USGS web pages for these 3 earthquakes:

  • 2015.11.17 M 6.5
  • 2015.11.17 M 5.4
  • 2015.11.18 M 4.7



This map (Hamilton, 2007) shows GPS vectors that represent secular motion of locations throughout this region. Note how the vectors on the lower part of the figure show larger motion to the west. At the latitudinal location of the NAF is where the vectors show a large change in magnitude. This shows how the NAF motion extends into Greece and is evidence for why the KF is the single through going fault system. I include the author’s figure caption below the figure as a blockquote.

Global Positioning System (satellite geodesy) velocity field of Aegean and Turkish region relative to internally stable northwest Eurasia. Velocities in the overriding plate increase along curving trajectories toward a south-facing subduction system. The trench is not shown but trends near SW and SE corners of map area, is convex southward, and is ~250 km south of Crete, the long island at bottom center. The overriding plate is being extended toward the retreating hinge (not shortened and crumpled against a fixed hinge), the free edge, as it is extruded between the converging Arabian and European plates. High-strain zones of strike slip and extension, not marked here, outline miniplates of lesser internal determination (Nyst and Thatcher, 2004). Other unmarked arc features: the forearc ridge (the crest of the active accretionary wedge) is ~100 km offshore from Peloponnisos (large peninsula of southern Greece, left center), 150 km south of Crete, and 100 km south of Turkish coast at far right; the magmatic arc is convex southward, and is 150 km north of Crete at closest. This image was slightly modified from a figure provided by Wayne Thatcher; cf. Nyst and Thatcher (2004, their Fig. 2).

There was a tsunami recorded, possibly from an observed landslide. The Eurpoen Commission hosts tide gage data online and here is the website for the tide gage in Crotone, Italy.
Here is the map that shows the location of this gage.


Here is the tide gage record.


Here is a photo that shows a landslide triggered by this earthquake. This was taken by a photographer for meteonews. This photo was posted on the International Tsunami Information Center listserv.


Here is a map from the University of Athens that shows the seismicity aligning with the KF.


Based on the PAGER estimate (an estimate generated by a numerical model that estimates ground shaking and the possible damage to people and their belongings), this earthquake could lead to up to 10 fatalities (30% probability). Also, there is a 34% probability that there is damage to their infrastructure of between 10 and 100 million USD.


For comparison, here is the map that shows results from the USGS “Did You Feel It?” online reporting web site. This is based upon real observations, not just modeled estimates (as the PAGER is above). For larger earthquakes, fault models are constructed and models are re-run to improve the PAGER estimates, but not in this case.


Here is another way of comparing the difference between the model based estimates and the real observations. Below is a plot showing the attenuation of shaking intensity with distance from the earthquake. The green and orange lines are the results of from the numerical model and the blue dots are the results from the observational reports. There is not a very good relation between these two data sets, likely because there is a paucity of observational data. But there assumptions about fault geometry of the numerical model also plays a big role as this model assumes a point location for the earthquake, while earthquakes are not point sources of ground motion.

Plate Tectonics: 200 Ma

Gibbons and others (2015) have put together a suite of geologic data (e.g. ages of geologic units, fossils), plate motion data (geometry of plates and ocean ridge spreading rates), and plate tectonic data (initiation and cessation of subduction or collision, obduction of ophiolites) to create a global plate tectonic map that spans the past 200 million years (Ma). Here is the facebook post that I first saw to include this video.
Here is a view of their tectonic map at a specific time.


Gibbons et al. (2015) created several animations using their plate tectonic model. I have embedded both of these videos below. Other versions of these files are placed on the NOAA Science on a Sphere Program website.

They also compare their model with P-wave tomographic analytical results. P-Wave tomography works similar to CT-scans. CT-scans are the the result of integrating X-Ray data, from many 3-D orientations, to model the 3-D spatial variations in density. “CT” is an acronym for “computed tomography.” Both are kinds of tomography. Here is a book about seismic tomography. Here is a paper from Goes et al. (2002) that discusses their model of the thermal structure of the uppermost mantle in North America as inferred from seismic tomography.
Here is an illustration from the wiki page that that attempts to help us visualize what tomography is.


P-Wave tomography uses Seismic P-Waves to model the 3-D spatial variation of Earth’s internal structure. P-Wave tomography is similar to Computed-Tomography of X-Rays because the P-wave sources are also in different spatial locations. For CT-scans, the variation in density is inferred with the model. For P-Wave tomography, the variation in seismic velocity. Typically, when seismic waves travel faster, they are travelling through old, cold, and more dense crust/lithosphere/mantle. Likewise, when seismic waves travel slower, they are travelling through relatively young, hot, and less dense crust/lithosphere/mantle.
Regions of Earth’s interior that have faster seismic velocities are often plotted in blue. Regions that have slower velocities are often plotted in red.
Here are their plots showing the velocity perturbation (faster or slower). I include the figure caption below the image.



Plate reconstructions superimposed on age-coded depth slices from P-wave seismic tomography (Li et al., 2008) using first-order assumptions of near-vertical slab sinking, with a) 3.0 and 1.2 cm/yr constant sinking rates in the upper and lower mantle, respectively, following Zahirovic et al. (2012), and b) 5.0 and 2.0 cm/yr upper and lower mantle sinking rates, respectively, following Replumaz et al. (2004). Both end-member sinking rates indicate bands of slab material (blue, S1–S2) offset southward from the Andean-style subduction zone along southern Lhasa, consistentwith the interpretations of Tethyan subducted slabs by Hafkenscheid et al. (2006). However, although the P-wave tomography provides higher resolution than S-wave tomography, the amplitude of the velocity perturbation is significantly lower in oceanic regions (e.g., S2) and the southern hemisphere due to continental sampling biases. Orthographic projection centered on 0°N, 90°E.

Earthquake in Crete

We just had a M = 6.0 earthquake in Crete. Here is the USGS web page for this earthquake.
This is an interesting region tectonically. The convergence of the Africa-India-Australia plates northwards towards the Eurasian plate runs from west of Europe, through the Middle East, through the Himalayas, out east towards the north side of Australia. As this large convergent plate boundary passes through these regions, it makes bends and these bends make the plate boundary have all the different types of faults (convergent, divergent, and strike-slip).
The plate boundary in the Crete-Greece-Turkey region is debated in the literature. There are different interpretations about what the faults are doing in this region. I will post a couple different maps below showing these different interpretations. (They probably are not all correct, but there may be tectonic “truths” in each of them.)
Here is a map that I put together that shows a simplified version of the plate boundary, showing one interpretation that favors some obliquity to the plate boundary on the eastern side of this map. I have placed the USGS moment tensor to show that this earthquake has a strike-slip sense of motion. I do not know which of the two fault plane solutions is correct, due to the wide range of different tectonic maps of this region. Before today, I did not know much about this area (just a general understanding of some of it). I love when these earthquakes happen because it gives me a change to learn about the different interpretations around the world…
I have placed the two options for the two fault plane solutions (right-lateral or left-lateral). Remember, when you are on one side of a strike-slip fault and you are looking across the fault to your friend, if they move to your right (and you move to their right, from their perspective), you are looking across a right-lateral (dextral) strike-slip fault. The obliquity of the plate boundary here is depicted as a right-lateral (oblique) plate boundary fault. Based upon this, I suspect that the fault is not the ~east-west striking left-lateral fault solution, but the ~north-south striking right-lateral fault solution. I may be wrong and someone who works in this area could correct me.


This is the USGS Intensity map that uses the Modified Mercalli Intensity Scale. It looks like this earthquake was felt across a broad region. Based upon the “Did You Feel It” map (composed of reports from real people, compared to this MMI map that is merely based upon a model), the MMI map is pretty good.


Here is a map that I found on the internets. It is from a Geological Society of America paper, but I cannot tell which (when I click on “take me to the page,” I get the log in page and it does not have any author information.) We can see their interpretation about how this plate boundary is more compressional on the west and transform on the east (at the Pliny and Strabo trenches). While there is conflict about the details, each map shares the sense of motion for the obliquity of the plate boundary here (right-lateral).


Here is another version from the Corith Rift Laboratory. This also shows right-lateral motion in this region.


Here is yet another map, also from a GSA paper. This one shows that there are a series of thrust faults, some with differing vergence (the direction that a thrust fault goes in when going from deep in the earth upwards to the surface). In my interpretation map above, the fault dips to the north, so is southward vergent.