The document analyzes borehole temperature data from across California to determine patterns between heat flow and geological location. It finds that regions closer to the coast have higher heat flow values, while more central locations have lower values. This difference is hypothesized to be the result of varying distances from the subduction of the Farallon Plate. Specifically, high heat flow regions lie on the outer arc of this subduction zone, while low heat flow values are found in the fore arc basin of the Great Valley. Understanding the relationship between heat flow and geology could help identify efficient sites for geothermal energy plants.

1. Empirical Analysis of Borehole Temperatures Located
throughout California specifically relating to heat flow.
Stephen Gronow, University of Akron – Ohio
1. ABSTRACT
The National Geothermal DataSystem,specificallyCaliforniaboreholetemperatures,was usedtofirst
calculate specificheatandthenanalyzedtofindpatternsbetweenheatflow andgeologiclocation.Heat
flowdatawere groupedinthree categories:Low (Q<=0.02 W/m2
),Medium(.1 W/m2
>Q<.02 W/m2
),and
high(Q=>.1 W/m2
). Boreholeswere then plottedusinglongitude andlatitude onamap of California
displayingone of the three heatflowcategories.Datawasinspectedthroughvisualization. Regions
closerto coast of Californiahada highvalue forheatflow while valueslocatedcentrallyhad low heat
flowvalues.The difference inthe heatflow betweenthe geologicpositionswashypothesizedtobe the
resultof distance fromthe subductionof the FarallonPlate.More specifically,the highheatflow region
liesonan outerarc while the lowheatflow valueslieona fore arc basin.
2. INTRODUCTION
The boreholesinCaliforniavaryby manyparameters,includingbutnotlimitedto:depthdrilled,
geographiclocation,andboreholetemperature.Thereare about12,000 borehole locations inCalifornia.
Dependingonheatflow, some boreholelocationspresentoptimum sitesforgeothermal energy.With
the growingdemandforcleanenergysources,it importanttoassessif there are any geological
processesthatcan be correlatedto highervaluedheatflow locations.Understandingthe relationship
betweenheatflow andgeologiclocationisessential fordetermining costefficientsitesforgeothermal
energyplants.
3. METHODS
Parametersfromthe National GeothermalDataSystemwere mergedandimportedtoaspreadsheetfor
analysis.Datawere manipulatedinordertosolve forheatflow usingFourierequation(Q= -K(ΔT/ΔD).
Note that an average of 2.5 W/mKwas usedforthe thermal conductivity. HeatFlow datawere
organizedintothree groups:Low (Q<=0.02 W/m2
),Medium(.1W/m2
>Q<.02 W/m2
),andhigh(Q=>.1
W/m2
).Heatflowdata points were mappedontoCaliforniavia LongitudesandLatitudes.Datawas
analyzedbyvisual inspection.
4. DATA DESCRIPTION
Whenheatflowwasmappedvialongitude andlatitude onCalifornia(Figure 1),patternsemerge.There
are prominentregionswithhighspatial densitiesof low andhighheatflow values thatare located
spatially close (observered circle Figure 1). Alsoshownare eachheatflow groupgraphedindividually
(Figure 2,Figure 3, Figure 4).
5. INTERPRETATION
The regionwithhighlocalizedheatflow values(Figure 1) isinterpretedtohave bedrockmade up of
volcanicrock due to the Franciscansubductionprocess.(Bartow andNilsen1990) The regionwithlow
localizedheatflowvalues (Figure 1) isinterpretedtohave layersof marine sedimentsdue tothe Great
Valleysequence.(BartowandNilsen1990)

2. 6. DISCUSSION
The regionwithhighheatflowvaluesisgeologicallylocatedon anouterarc. Specifically,the regionwas
made by the Franciscansubductionprocess.Due toitslocationneara subductioncomplex,the heat
flowtemperaturesare significantlyhigherhere.(Bartow andNilsen1990) On the otherhand,the region
locatedgeologicallywithinthe fore arcbasinisknownas the Great Valley.Due tothe basinbeing
furtherawayfrom the subductionzone the heatflow tempsare cooler.(Bartow andNilsen1990)
Consequently,itwouldbe more efficienttoputa geothermal energyplant onanouterarc (See Figure 5
for general picture of subductionzone)
7. CONCLUSION
The purpose of thislab wasto betterunderstandthe geothermal energyof differentgeologiclocations
withinCaliforniabasedonheatflow. Itwasfoundthatthe regionthat had highheatflow valueswere
geologicallylocatedonanouterarc. Adversely,the regionwithlow heatvalueswasgeologicallylocated
on a fore arc basin. Basedonthe findings,apossible location tobuildageothermal energyplantin
Californiawouldbe onthe outerarc,specificallynearSanta Rosa.
8. CITATIONS
Bartow,J. and T. Nilsen.1990. Reviewof the GreatValleysequence,easternDiabloRange andnorthern
San JoaquinValley,central California.Departmentof the InteriorU.S.Geological Survey:1-25.
WilliamP.Elder,Geologyof the GoldenGate Headlands,National ParkService,GoldenGate National
RecreationArea, from,Stoffer,P.W.,andGordon,L.C.,eds.,2001, GeologyandNatural History
of the San FranciscoBay Area:A Field-TripGuidebook,U.S.Geological SurveyBulletin2188, p.
61-86.

3. APPENDIXA
Figure 1. Borehole locationsinCaliforniaclassifiedbyheatflow,notice regionencircledbyred
boundary.

4. Figure 2. Borehole locationsinCaliforniaregardinghighheatflow,notice locationof highvaluesare
alongthe westcoast.

5. Figure 3. Borehole locationsinCaliforniaregardinghighmediumflow,notice mediumvaluesare located
nearthe westcoast.

6. Figure 4. Borehole locationsinCaliforniaregarding low heatflow,notice low valuesare locatedinthe
Great Valley.

7. Figure 5. Great ValleySequence presentedbyGeocaching.com takenfromWilliamElder.